Sunday, May 31, 2009

Apple #387: Ant Muscles

I'm supposed to do another entry about the plants I saw while on my trip to California. But I'm short on time tonight, so I'm doing a shorter entry instead. I'll get to those sequoias this week, I promise!

So I was walking with my co-worker to the next building where we have to go to pick up the mail when I spotted an ant zooming at lightning speed across the sidewalk. I pointed this out, saying something very articulate like, "Look at that ant go!" My co-worker responded by saying something about the ant's muscles. "Those ant muscles are really working," or something to that effect.

"Ants have muscles?" I said.

"Sure," said my co-worker. "How do you think they move?"

"I don't know. I thought they just had exoskeletons."

"But all animals have muscles. They couldn't move without them."

Here again, words failed me. Nobody in my science classes had ever said anything about ants having muscles. All anybody ever told me about ants were that they had 3 parts to the body -- head, thorax, abdomen -- and those were covered in exoskeleton. Never a peep about any muscles. And those ant legs are so skinny. Are there really muscles somewhere in there?

We all recognize that ants are strong and fast. So where are their muscles?
(Photo of leaf-cutter ant from

  • Ant muscles are a fairly well-kept secret; even now, with all this free online knowledge, people don't talk about them much.
  • Most of the time, what scientists have to say about ant muscles is that they are not, in fact, super-strong compared to human muscles. A lot of people think that, since ants can carry loads that are way huger than the size of their bodies, ant muscles must be phenomenally strong. But this is not the case. The reason ants can carry such huge loads (compared to what humans can carry) is that their body weight is relatively light while the proportion of muscle-to-body-mass is greater. Their muscles don't have to work as hard to carry around their ant bodies, so the muscles have lots of strength-capacity left over to carry other stuff. If our muscles didn't have to work so hard carrying us around, we'd be able to heft enormous things, too.
  • Even as scientists are answering these sorts of questions about ant muscles, they never say where those ant muscles are.
  • Other ant scientists answer questions about how ants eat, how they walk, and that sort of thing. In service of answering those questions, they typically provide anatomical diagrams of ants, like the one below. But nowhere on those anatomical diagrams do they point out the freakin' muscles.

This particular anatomical chart of a worker ant gets very specific, even to the point of indicating the femur and tibia. But it does not mention anything about leg muscles.
(Diagram from Wikipedia)

  • Biologists do talk sometimes about a particular set of muscles -- the ones in the ant's head which operate the ant's mandibles. These muscles are huge, in ant terms. Some ants in particular, like the trap jaw ant, have especially enormous mandibles and correspondingly enormous muscles that work the mandibles.
  • Mandibles are the ant's jaws. Ants trap their food in the mandibles and then they literally squeeze the life out of the food. Then they keep squeezing out all the moisture from the food. They drink that liquid and then toss aside the solid matter. So the ant needs really strong muscles to accomplish all that squeezing. Trap jaw ants also use their mandibles to help them escape from predators [movie]. (For more about that movie see my entry on the speed of ants.)

Drawing from 1927 of the muscles in an ant's head which operate the mandible. But these aren't leg muscles.
(Diagram from Wikipedia)

  • One pair of scientists, Birgit Ehmer and Wulfila Gronenberg, got way interested in the muscles that operate an ant's antennae. Birgit and Wulfila had 10 pages' worth of observations to make about ant antennae muscles. While no doubt fascinating, this was not the kind of ant muscle action I was after.
  • After some time of not finding anything about ant muscles, I started to guess. I looked at close-up photos of ants and I wondered if the places on their legs that get wider are the places that contain muscles. For example, what amounts to the thigh on this ant looks relatively muscular.

You don't want to meet one of these ants in real life. This is a bullet ant, native to Belize. Its sting is so powerful, people say it feels like you've been shot with a bullet. The pain from the sting feels like "waves of burning, throbbing, all-consuming pain" that lasts for 24 hours.
(Photo from Guide to Belize)

  • Finally, I found the answer I was looking for. The second section of the ant's body, called the mesosoma, "is packed full of muscles" that operate the ant's six legs.

In this diagram, the pink section called the mesosoma is where most of the ant's motion-related muscles are contained. In the diagram at the top of this entry, that same section is called the Alitrunk. Most of us call that section the thorax.
(Diagram from ASU's Ask a Biologist)

  • According to a book on entomology, the muscles in the thorax (a.k.a. the mesosoma) extend out to the first joint of the ant's leg, called the coxa. There is a pair of muscles (adductors and abductors) on either side of the coxa that help the ant move the legs back and forth. There is another pair of muscles (levators and depressors) that help the ant lift the leg and put it back down.
  • In the ant, most of the muscles are around the coxa and the femur, but a few of them are also around the tibia. So my guess based on looking at the bullet ant photo wasn't that far off.
  • I also learned this other ant muscle fact: when the queen ant has lain her eggs and is nesting, she doesn't leave the eggs, so the worker ants bring her food. But she needs still more food. So the muscles that once supported her wings, which are also in the thorax, get absorbed into her body to supply her with extra nutrition.

There you have it. Ants do have leg muscles. They're even somewhat similar to the leg muscles that you and I have, albeit very tiny. The cloak of mystery that has shielded us from the truth about ant muscles has been thrown back, thanks to your Apple Lady.

If you liked this, you might also be interested in this entry about the speed of ants.

Rob Campbell, MadSci Network, How can ants carry so much weight in proportion to their size?
Howstuffworks, Ant
Arizona State University, Ask a Biologist, Face to Face with Ants
Cedric Gillott, Entomology, second edition, pages 424-426. Thanks, Google Books!
Encyclopedia Britannica, insect, Form and Function, External Features, thorax, Dictionary of Zoology, coxa
C. Claiborne Ray, "Ant Power," The New York Times, November 20, 2007

Saturday, May 30, 2009

Apple #386: Light Bulbs

The night before I left for my trip, I was up very late (surprise, surprise), taking a shower. My shower is in the basement, and dimly lit. I had a clip-on desk lamp that I had clipped to the side of the shower so that the bulb would shine right into the shower and make it much easier for me to see.

So I was showering away, happy as a very tired clam, when all of a sudden there was a great POP! and I felt something sting my shoulder and heard a lot of glass tinkling. I realized the light bulb in my clip-on desk lamp had exploded, and the floor of the shower was full of broken light bulb glass. The stinging on my shoulder was from where one of the shards of light bulb glass had landed. It hadn't cut me; rather, because the glass was so hot, it burned my skin in a patch exactly the same shape as the piece of glass. Weeks later, I still have a mark there.

All that's left of the light bulb that exploded in my desk lamp.
(Photo by the Apple Lady)

Naturally, this got me thinking about light bulbs and what makes them explode.

Why Light Bulbs Explode
  • Lots of people say that poor-quality, off-brand light bulbs are prone to exploding. This is because the off-brand bulbs typically aren't sealed well, and they allow air to leak into the interior of the bulb, which can cause an explosion. Yeah, this was probably a cheap, grocery-store brand of bulb that I had in there.
  • If the light bulb is hot enough and even a few drops of cold water land on the bulb, the cold will make the glass contract unevenly in that spot where the cold water hit it, and the light bulb can explode. I don't think this was the cause in my situation because I was in the shower and the water was hot, not cold. But still, that's good to know.
  • If the light bulb had flickered before exploding (it did not), that could indicate a bad electrical connection -- faulty or old wiring, perhaps. That poor connection could send spikes of power to the bulb, causing it to overheat, which would in turn put too much stress on the glass, which would then explode.
  • It is also possible that as a light bulb gets old, the filament which is pretty much the glowing part that carries the light & heat from one pole to the next inside the bulb gets weaker and weaker. Most of the time, the filament snaps and the bulb just plain burns out. But sometimes the filament can sort of fly off at one end, or arc. If the arc keeps burning, a lot of heat and pressure can build up inside the bulb very quickly, which could cause the glass to shatter.
  • Power surges can also cause light bulbs to explode. Lots of people report power surges happening after lightning struck very close to the house, and the resulting surge of electricity blew out most or all of the light bulbs in the house. This slow-motion video shows a light bulb pulsing with what looks like some sort of power surge before it explodes.

(Diagram of a light bulb from

How the Explosion Happens

What is actually happening during the explosion is a nice bit of science fun.

  • The inside of the bulb is filled with inert gases like argon and nitrogen. Those gases displace the regular old air that you and I breathe, and the light bulb is sealed up with those gases in there. That creates a vacuum.
  • The reason you want a vacuum inside a light bulb is because the filament will burn longer. If you've got too much oxygen (which is present in regular air) the filament, no matter what material it's made of, will burn up in a couple of seconds. If you remove all the oxygen, the filament won't burn at all. The inert gases allow the filament to glow instead of burning. In addition, the gases carry the radiant heat out to the glass, which makes the entire interior of the bulb glow.
  • Another important piece of light bulb construction is the strength of the glass. Once the inside of the bulb is a vacuum, the pressure of the outside air is going to push in against the glass. If the glass is weak and cheap, it'll break and the outside air will rush in. Better-made bulbs use thicker glass that better withstands pressure from the outside air.
  • Regardless of the thickness of the glass, it is still possible that the glass might develop a crack, or a leak somewhere. If that happens, air from the outside of the bulb rushes in. Since the outside air is at a higher pressure than the no air inside the bulb, that new air pushes against the glass from the inside out, resulting in an explosion.
This video explains how a light bulb works and shows in super slow motion how the tungsten filament begins to glow. At the end of it, the light bulb explodes. From the way the filament is dangling, I would guess that explosion was caused by the filament arcing.

Light Bulbs with Mercury Inside 'em

What I've been describing are incandescent light bulbs. These types of bulbs, after more than 100 years of service, have been declared to be energy-inefficient. The European Commission have decided that by 2012, incandescent light bulbs will are to be permanently phased out. Australia is giving incandescents the boot by 2010. Lots of people who care about the environment have said that incandescent bulbs are not energy-efficient enough and that we should find alternatives.

So people have been developing alternatives. One type that you've probably heard about is known as the Compact Fluorescent Lamps, or CFLs. The US Energy Star program, for one, says of these bulbs

If every American home replaced just one standard incandescent light bulb with a long-lasting CFL, the resultant energy savings would eliminate greenhouse gases equal to the emissions of 800,000 cars.

So I've bought into this. I have three CFLs currently in use in various fixtures around my house. The oldest one I put into the fixture four years ago. Still working just fine.

However, these bulbs contain mercury. After my cheap-o incandescent bulb exploded all over my shower, I thought, what if that had been one of those CFLs with mercury inside it?

A compact fluorescent lamp (CFL) with the Hg symbol on it. As you probably remember from your high school chemistry class, Hg is the chemical symbol for mercury.
(Photo from

  • Remember when everybody got all concerned about the mercury in thermometers, and we all had to throw out our old, bad, dangerous mercury thermometers and get new ones?
  • Just in case you don't remember or never heard, mercury is a neurotoxin. That means it damages nerve cells, and in a hurry. Even in very small amounts, it can cause brain damage, seizures, and even kill you.

What a blob of mercury looks like when it's on the loose, so to speak. Really cool, and really dangerous. There is only a tiny percentage of this amount of mercury -- in powder form -- in CFL bulbs.
(GNFDL photo sourced from World News Network)

  • So, if we were so concerned about mercury in our thermometers, why aren't we concerned about it now, when it's in our light bulbs?
  • People argue that the amount of mercury contained in these bulbs has less of an impact than the incandescent bulbs. They say this because the electricity which feeds into the light bulbs is still predominantly made by coal-fired power plants, which send a heck of a lot more mercury in gaseous form into the air than the CFL bulbs have inside them.
  • In fact, there's a ton -- literally -- more mercury coming out of power plants than there is coming out of light bulbs. In 1999, the EPA estimated that coal-fired power plants were emitting an average of 48 tons of vaporized mercury into the air per year. That's more than all other sources of human-made mercury combined.
  • Yet another reason the mercury produced by power plants is more of a concern than the mercury in a light bulb is because mercury in the air is far more toxic than a blob of mercury on the floor. Once it can gets into your lungs, you will breathe it over and over.
  • But those power plants aren't shooting the mercury directly into your house, right? (Or at least, you like to think they aren't.) Whereas those light bulbs with the mercury in them, those are in your house.
  • So let's say you have one of the CFL light bulbs, and you drop it, and it breaks. Out comes the mercury powder. That's only about 4-5 milligrams of mercury. (Those old thermometers, by the way, had 500 milligram blobs of mercury in them.)
  • Sure, it's just a little bit of powder, but it's still mercury. If you touch it, the mercury will be absorbed through your skin. If you eat it, that's even worse. Nerve damage, seizures, death. We get it. This is why the packaging on most CFL bulbs has explicit instructions about not touching the mercury or not eating it.

Those recommendations, in brief are:
  1. Open the windows immediately to less the concentration of vaporizing mercury in the air in your home.
  2. Turn off the air conditioning or forced-air furnace.
  3. Do not touch the spilled mercury.
  4. Do not use a vacuum cleaner to clean up the glass or the mercury, as it will vaporize the mercury faster.
  5. Clean up the broken glass carefully and immediately, while wearing gloves and sliding the broken glass and mercury powder onto something disposable yet sturdy like stiff cardboard.
  6. Use sticky tape to remove any leftover fragments or mercury.
  7. Wipe the place where the spill happened with clean, damp paper towels.
  8. Place all the paper towel and gloves and whatever else you used to clean up the mercury into a sealed plastic bag, and take the bag to your friendly, local Household Hazardous Waste collection site.
  9. (More detailed tips on cleaning up a broken CFL bulb are available here and still more details are available here)

Of course some enterprising individuals are capitalizing on this problem. Which is not necessarily bad. One company sells this CFL clean-up kit, which includes things like thick gloves, shoe covers, face masks, and wet wipes, for $9.99.
(Photo from CFL Clean-Up Kits)

  • But let's pretend that you neither touch nor eat the mercury powder. Let's pretend that the mercury powder sits there on the kitchen floor for a while. Eventually, it will evaporate.
  • Even if that mercury powder on your kitchen floor evaporated instantly, creating the highest possible concentration of vaporized mercury in your home, that concentration would amount to only 0.2mg/m^3. In layperson's terms, that is less than half of the level at which OSHA thinks mercury in the air is dangerous. Furthermore, that airborne mercury will dissipate over time, further reducing the concentration of mercury and the amount that could get into your lungs.
  • You can wash your clothes, you can air out your house, you can toss out the paper towels you used to wipe up the spill. But it's a lot harder to get rid of those 48 tons per year of mercury that are floating around in the air and getting into the water and the fish and the soil.
  • So people say that CFLs have such a comparatively small concentration of mercury in them, that amount of mercury is manageable, and thanks to Home Depot's help, you can safely dispose of the bulbs. And the amount of energy you'll save by using CFLs will actually reduce the amount of mercury being pumped out by those power plants.

Still, I'm going to put out a call for research. Very officially. Hey, scientists, will you figure out what to do with the mercury? And find something less toxic to put in these light bulbs? Thanks.

For more information on how to handle a mercury spill, and links to places where you can recycle your CFL bulbs, check out the EPA's site on mercury spills.

The Dollar Stretcher, Exploding Light Bulbs
MSN Q&A, Could a power surge really make a light bulb explode (cached), Light bulb exploding, May 2, 2009
InterNACHI, Exploding light bulbs
"Experts doubt exploding light bulb theory,"
St. Petersburg Times, April 7, 2005
Sawaal, Why does an electric bulb explode when it is broken? September 4, 2007
WikiAnswers, How does a light bulb work?
Howstuffworks, Light bulbs: The filament
Theodore Gray, You Do It: Make Your Own Light Bulb, (not for beginners) Live Science, February 27, 2006
James Kanter, Kissing Edison's Light Bulb Goodbye,
The New York Times, March 18, 2009
Elizabeth Shogren, "CFL Bulbs Have One Hitch: Toxic Mercury," NPR, All Things Considered, February 15, 2007
Northeast States for Coordinated Air Use Management, Mercury Emissions from Coal-Fired Power Plants: The Case for Regulatory Action, (PDF) October 2003
Helen Suh MacIntosh, Is Mercury from a Broken CFL Dangerous? Ask TreeHugger, May 1, 2007, Energy-saving bulbs (CFLs) release dangerous amounts of mercury when broken
Julia Layton, Is the amount of mercury in CFLs more dangerous than the amount in fish? Howstuffworks

Tuesday, May 26, 2009

Apple #385: Manzanita plants

Now for another entry about the things I encountered during my recent trip to California.

As I was wandering around up in the hills of the high desert in southern California and looking at all the really fantastic plants around me, I noticed that the branches of one plant were two different colors. Some looked all dried out and dead-gray, and others were a bright red. Crazy! thought I.

I thought maybe one plant was growing right up next to another one, and that this was just a fluke. But I turned around, and there was another one. It was doing exactly the same thing.

I straightened up and looked about me and realized I was standing in a whole grove of these things. It was almost like an orchard that somebody had once planted and then abandoned. They were growing all over the place.

Only a small portion of the maybe hundreds of these plants growing on the north side of the hill.
(Photo by me, the Apple Lady)

I have since learned that the name for a whole bunch of plants growing together like this is "community."

After a few hours of walking around up there, I went into town into the local library. I was looking through some books they had about native desert plants, comparing the photos on my camera to the photos in the book, when a kind soul sitting across the table from me asked if I was looking up local plants, and was I trying to identify them. Yes, I was, I said.

His name was Oliver, he told me, and he very kindly looked at my photos of this odd plant and said right away that it was Big Berry Manzanita. Except first he told me the genus and species name (Arctostaphylos glauca). I blinked at him and asked him for the common name.

Big Berry Manzanita (according to Oliver)
(Photo by the Apple Lady)

It turned out he could identify nearly all the plants I had taken pictures of by both the genus and species name. He rattled these things off like they were his first and last name. So Oliver was extraordinarily helpful. Most of the plants whose pictures I may share with you in coming entries will probably be identified courtesy of Oliver's help.

Close-up of the leaves of the Big Berry Manzanita. Lots of the photos of this plant that I've seen online have a whitish-gray (glaucus) cast to them, and they look dusty. These leaves look pretty shiny to me. But one California nursery's site says that the Big Berry Manzanitas do well in very hot regions, including the Joshua tree woodlands. On the south side of this hill is where I saw all those Joshua trees. So even though these leaves don't look glaucus to me, I'm sticking with Oliver's identification -- Arctostaphylus glauca.
(Photo by the Apple Lady)

  • There are all sorts of different species that get called by the common name of Manzanita. Some sources say 50, some say 76, others say as many as 106. Most of them grow in California, but some also grow in other places like Arizona and New Mexico, the Atlantic seaboard (Florida, Alabama, etc.), and even as far north as Canada.
  • Manzanita is Spanish for "little apple" because when these plants produce fruit, they do look like little apples.

I had thought these were berries, but Oliver told me they are actually galls. Galls, he explained, happen when insects burrow into the leaves or bark of a plant and lay their eggs in the tissue. The plant produces a lot of goo that swells up around the opening the bug has made -- sort of like a blister, I guess -- and the insect larva lives in there. Now that I know those are essentially bug pods, it makes me feel all itchy and crawly to look at them. Aren't you glad I shared this piece of knowledge with you?
(Photo by the Apple Lady)

This is what the berries of the Big Berry Manzanita actually look like.
(Photo from Las Pilitas Nursery)

  • You can eat the berries and the flowers, too.
  • You can also make a cider-like drink with the berries, but don't go on a long trip afterwards because it's a pretty strong diuretic.
  • People have also used the bark to make tea, which supposedly helps to assuage nausea.
  • Butterflies and hummingbirds also like the flowers. In fact, as I was standing on the crest of the hill where these manzanitas grew, a really loud buzzing sound shot right past my left shoulder and I barely had time to whip my head around and see that it was a green hummingbird that had zoomed past me.
  • Manzanitas are evergreen plants, which means they don't lose their leaves.

The fact that manzanitas are evergreens seems a little strange because I saw a lot of them with brown leaves like this. Not only were some of the leaves on this plant brown, it was as if someone had drawn a line down half of the plant; all the leaves on the left were brown while all the leaves on the right were green. I don't know if you can tell this from the photo, but what's even more strange is that the trunks in the green leaves are gray, while the trunks among the brown leaves are red.
(Photo by the Apple Lady)

  • The wood is orange or red because of all the tannins in it. Tannins are very bitter and, for some organisms, even toxic. So the tannins help protect the wood against bugs and animals. In addition, most manzanita bark peels off a layer each year, which helps to shed anything that might have grown on it in spite of the tannins.
  • People call manzanita "mountain driftwood" because the wood is so smooth and twists into such interesting shapes.
  • Because manzanita wood is so slow-growing, it's very dense, which makes it for good firewood because it will burn for a long time. Be careful if you're burning it in an oven or a chimney, though, because the wood can burn so hot it could crack even a cast-iron stove.
  • That's especially intriguing because botanists think that manzanitas originated about 15 million years ago and hybridized as the parent plants were burned up in fires. Some of the newer species will only produce viable seeds after a fire has heated up the plants.
  • It seems like these plants just keep getting associated with fire. One variety of manzanita plants is kinnikinnick, which a lot of native tribes used to smoke as tobacco or burn as offerings to the spirits.
  • One guy who makes his own pipes has made a few out of manzanita wood. They're pretty attractive.
  • People also like to use manzanita branches in aquariums because its tannins won't leach into the water. Bird-owners use manzanita as roosts for their pet birds because the twisty branches give the birds interesting things to hop and climb on, and the wood is smooth and strong.
  • Manzanitas are also becoming very popular to use in centerpieces. A lot of brides out there are frantically looking for manzanita branches. I'm not going to tell them where they can find these plants.

Here's some mountain driftwood for a bride's reception. Come on, it's nature.
(Photo by the Apple Lady)

USDA Plants Profile, Arctostaphylos Adans. manzanita
Jeff Schalau, Arizona Cooperative Extension, Backyard Gardener, Growing Manzanita, February 26, 2003
Guillermo Cabrera, Manzanita Park
Ron Sullivan and Joe Eaton, "Mysterious manzanita baffles homeowners,"
San Francisco Chronicle, May 7, 2008
Las Pilitas Nursery, Manzanitas from Central California
Mike Vasey, Why is manzanita bark so smooth and red? BayNature, April-June 2003
Geoffrey Coffey, "Manzanita charms Bay Area terrain," San Francisco Chronicle, December 18, 2002
Biology Online, gall

Sunday, May 17, 2009

Apple #384: Moths to the Light

So I know I said I was going to post a bunch of entries about my recent trip to California. But most of those entries have to do with plants. So instead of giving you a bunch of plant entries in a row and making you thoroughly sick and tired of plants, I thought I'd space them out a little bit.

So I'm going to tackle a question recently posed by faithful Daily Apple reader Tim, who asked:

Hey, I've got a Daily Apple question: Why do moths go toward the light? Had a beautiful moth bouncing around in here for a couple nights. What draws them to the light? If they like light so much, why don't they just get up in the daytime like the butterflies? Riddle me that!

I'm going to spare everyone the atrocity that would result if I tried to put the answer in a form of a riddle, or a rhyme even, and I'll just give you the facts. Or I should say, theories.

  • Most moths are nocturnal, so they wake up and go looking for food at night. They're not going to get up in the daytime like the butterflies because they're wired to do otherwise. This would be like the Apple Lady going to bed before midnight. Unthinkable!
  • Of the moths that are nocturnal, not all of them fly toward a light. But as for the ones that do, they tend to zoom toward the light bulb and ping around it for a while. Or, in the case of an open flame, they fly toward that and flutter around it and sometimes even fly into it and get incinerated.

  • So once again, we turn to the scientists for the answer to a "why" question. As I've learned in the years I've been doing this here Daily Apple, scientists are terrible when it comes to answering the "why." This case is no exception. They don't really know why moths fly toward the light. But they have some theories.
  • One theory that's probably the oldest, or anyway gets tossed around the most, is that because moths are nocturnal, they use the moon as their navigational reference point and they think that artificial lights are the moon.
  • Scientists have discovered that moths have a kind of internal compass (similar to that which Monarch butterflies have) which they use to keep themselves oriented at a certain angle relative to the moon. When the moths see an artificial light that they think is the moon, they fly toward it thinking that they will never actually get there but that it will remain far up in the sky and they will have to stay at that certain angle relative to the moon. But, surprise surprise, they do get to the moon (which is really the light bulb). This confuses the heck out of them, they back off, and then their navigational compass kicks in again, and they try to maintain that angle relative to the moon/light bulb, only to fly into it once more.

If you're a moth with a miniscule brain, would you know which of these lights is the moon?
(Photo by Olga Levina)

  • A few moth scientists don't like this theory so much. They say the patterns of moths' flight as they circle the moon/light bulb don't match up with the patterns that would result if the magical navigation-angle theory were true. I'm also wondering, if moths are so easily confused by artificial lights, how the heck do they manage to get where they're supposed to go, especially if they're migrating moths?
  • One moth scientist in particular, Henry Hsiao, has proposed another theory, which has two parts. The first of these is that moths are trying to protect themselves from predators. If a moth is sitting on a bush, let's say, and something is sneaking up from the ground to eat it, the moth is going to fly away. To a moth active at night, dark equals ground while light equals sky and moon and therefore safety. So according to this theory, when a moth zooms toward a light bulb, some predator has just tried to eat it and the moth has just flown like a bat out of hell to get away from it and, surprise, finds itself at the moon.
  • Once the moth is at the moon/light bulb, the moth realizes it's too close and tries to get away, or back to the darkness. However, surrounding every light source is a thing called the Mach band, which is a darker band of light. The moth thinks this darker band of light is the actual darkness and it circles around the light, trying to keep itself in the Mach band which is about a foot away from the light.

Look at the white circle of light in the middle of the purple. After a second or two, you'll notice a darker ring of purple about halfway out from the middle of the circle. This darker circle is not actually there; it's only an illusion produced by the eye. This darker circle is what is called the Mach band, and it's what Dr. Hsiao thinks that the moths try to keep themselves in as they're circling a light bulb.
(Image from Perceptual Stuff)

  • I have some problems with this theory, though, too. If this were true, the moth would fly in concentric circles and it would not keep going back to the light bulb, pinging off it, and back again. Also, why does light equal safety when the moth is in the bushes, but then when the moth is at the light, the moth decides that dark equals safety? And that Mach band is pretty small, especially compared to all the dark outside the circle. It's tough for me to believe that the moths really prefer the Mach band to all the dark that's farther outside of the circle.
  • It's also worth noting that Dr. Hsiao's theory includes the assumption that the moths are confusing the artificial light with the moon. In part one of his theory, they're assuming the light equals the moon and that they should fly toward it. So I don't see him necessarily contradicting the moon theory after all.
  • But what about when the light source is a candle? One scientist named Philip S. Callanan did a bunch of work with optics and infrared rays, and he said that it is male moths who are flying toward the candles, and they're following their sense of smell as well as sight. Callanan says that moths use a combination of smell and sensitivity to infrared light patterns to detect the presence of female pheromones. A candle emits an infrared spectra of light that's really similar to that of a female moth, so the male moth flies toward the candle expecting it to be a female moth. And then the male tries to mate with the supposed female, but instead gets scorched.

Moth flying toward a candle.
(Photo by Tony)

  • This doesn't account for the moths' behavior around light bulbs, though, so I'm dissatisfied with it.
  • Another scientist says that when the light source is flame, the moth has no "evolutionary history" to tell it that the heat associated with the flame is too hot and that it should not fly straight into it. It's flying to the flame, thinking it's the moon, but because it doesn't know to avoid heat, it gets toasted.
  • At first this seemed pretty ridiculous to me because flames have been around for a lot longer than light bulbs. I mean, when there's a forest fire, are all the moths just diving into the fire? But it turns out, somebody researched exactly this, and yes, the researchers saw the moths heading straight into the fire.
  • Elizabeth Gerson and Rick Kelsey, who work for the US Forest Service, did an experiment using pandora moths that live in Oregon. They caught about 200 of the pandora moths in two light traps, and then they set a controlled fire near the traps. They put the traps on the ground near the fire, opened the traps, and watched what the moths did. Very few moths flew out of the light trap. Of those that flew, three of them "spiralled into the flames." Most of the moths crawled out instead of flying, and half of those that crawled out walked straight into the fire and burned. "Radiant heat did not seem to deter pandora moths from entering the flames."

Coloradia pandora, the moth that Gerson and Kelsey saw walking into the fire. I think that unit of measurement is centimeters.
(Photo from Moths of Southeastern Arizona)

  • Even though I have seen a moth fly into a candle, I find this utterly shocking, that moths would walk straight into a forest fire. I mean, where's the sense in that?
  • By the way, this study also tested the moths' responses to different colors of infrared light. They found that the moths didn't seem to care what color the light was, which suggests that Callanan's theory is a bit wobbly. Callanan and Gerson were each testing different species of moths, so it's possible they could both be true. But I find Gerson's study in which they saw the moths walking into the fire to be more compelling.

Apparently if you're a moth, when you see a fire like this, you say, "Hey, wow, I want to get right in the middle of that."
(Photo of a forest fire near Big Bear Lake, CA by Fotoguy77, I think)

Man, I just can't get over that. I ask again, how does that make any kind of sense?

Well, after all this, I haven't answered Tim's question -- at least, not to my satisfaction. But it looks like the light bulb = moon theory seems to be the one that's winning. That is, this is the best theory scientists have right now, until somebody does some more research and maybe finds out that moths are doing something other than confusing the moon and light bulbs.

For now, I think the short answer is, "Moths fly to the light because they're stupid." Along those lines, these people are demonstrating for us the logic of moths. Except they have sense enough to quit after a while.

P.S. After calling all moths stupid, I have to amend my statement. Because I remembered the moths we learned about in the Joshua Trees entry, the ones who are solely responsible for pollinating those wacky and friendly plants. So I'm going to say that the ones who do not head straight for the flames -- in Gerson and Kelsey's study, that was slightly less than half -- those moths are not as stupid.

The Straight Dope, Why are moths attracted to bright lights? January 27, 1989
Howstuffworks, Why are moths attracted to light?
NPR All Things Considered, Why are Moths Attracted to Flame? August 18, 2007
Happy News, Why Are Moths Attracted to Light? September 26, 2007
James K. Adams, Why are moths attracted to lights . . .
Wikipedia, Moths
Philip S. Callanan, Moth and candle: the candle flame as sexual mimic of the coded infrared wavelengths from a moth sex scent (pheromone),
Applied Optics, December 1, 1977
James L. Oschman and Nora H. Oschman, Electromagnetic communication and olfaction in insects,
Frontier Perspectives, September 22, 2004
Elizabeth A. Gerson and Rick G. Kelsey, "Attraction and direct mortality of pandora moths, Coloradia pandora (Lepidoptera: Saturniidae), by nocturnal fire," Forest Ecology and Management, October 22, 1997

Tuesday, May 12, 2009

Apple #383: Joshua Trees

All right, I'm back from my trip. And I have many questions, of course. I took a lot of photos with my new camera mainly of plants, so a lot of my questions have to do with plants.

The first plant I encountered which made my jaw drop at its sheer insanity was the Joshua tree. I had no idea what they were when I first saw them and they looked to me like something straight out of The Lorax.

The Lorax and the Truffula trees, which he turns into thneeds. Everyone needs a thneed, right?
(You can get a painting of this image from Tiffany Duening at SprayGraphic)

A stand of Joshua trees, Palmdale, CA. Don't they look a lot like those Truffula trees?
(Photo by the Apple Lady. How exciting that I get to say that!)

All of these photos, by the way, were taken in Palmdale, California, which is in the Mojave Desert.

Apparently, I'm not the only one who confused Joshua trees with something else. They have been misunderstood, reminded people of other things, and mis-named several times.
  • Natives who lived in this area for centuries called the tree "hunuvat chiy'a." That's not really a misunderstanding or misnaming, it's just an alternate name.
  • German immigrants thought they looked like the prophet Joshua praying to God with upraised arms and pointing the Israelites to the Promised land. So they called them Joshua trees.
  • Other German settlers who came to the Antelope Valley where lots of these trees grow thought they were date palm trees. So they named the place Palmenthal, which later became Palmdale.
  • In fact, they're not even trees. They are Yucca plants, which used to be classified as part of the lily family (now they're grouped with Agaves).
  • The full Latin name for the Joshua tree is Yucca brevifolia. It is closely related to the Mojave yucca, the Yucca schidigera. The two plants often grow near each other, and they look very similar except the Mojave yucca's leaves are wider and longer, and there are fibrous threads that stick out from the edges of the leaves. I don't think I have any photos of the Mojave yucca, but if any of you plant enthusiasts out there spot a misidentification, please let me know.

Another thing that makes them look weird is the bark. The spines on the top dry up and turn gray as the plant grows, but they don't fall off. They stay shaggy on the trunk. In the photo below, you can see that on the trunk on the left.

Joshua tree trunks.
(Photo by the Apple Lady)

Some of the trunks didn't have that shaggy stuff on them. On the trunk in the foreground, you can plainly see the bark, no shaggy old spines on it. Eventually the shaggy spines drop off, exposing the bark. But based on the fact that I saw so few exposed trunks, I'm guessing it takes a long time for the spines to drop off.

As far as plants go, there are a lot of unusual things about Joshua trees.
  • They are monocots, which among other things means they are a flowering plant and the vascular tissue that goes up the stem to feed the plant is scattered throughout the stem, not bundled into a single ring.
  • This means they don't have growth rings so you can't figure their age that way.
  • Based on guesses about the growth rate of the plants, some of the oldest trees are estimated to be between 800 and 1,000 years old.
  • The old ones can get to be anywhere from 30 to 80 feet tall.

The Joshua tree sticking up was much taller than the others I encountered in the area. I'm really bad at guessing heights and distances, but I put this one at maybe 10 or 12 feet tall. It might be even taller than that, though.
(Photo by the Apple Lady)

  • It's rare, though, for the trees to get that tall because of the way they grow. They grow vertically until a blossom starts at the knob-end of the branch. The new growth will veer off to the side and continue from there. That's how they wind up looking all twisty.

The almost right angle turns in the Joshua tree branches are where it has blossomed in the past and the new growth has veered off from there in another direction. To the left of the Joshua tree is a silver cholla cactus.
(Photo by the Apple Lady. That's me!)

  • The roots go only about 2 or 3 feet deep underground. But at the end of the roots are large bulbs which act as reservoirs that hold water. The importance of these bulbs and the fragility of the roots are what makes the Joshua tree very difficult to transplant.
  • Joshua trees will bloom only if the plants have the right amount of rainwater and if temperatures are right. There is a saying that they bloom only every seven years, but that's only an indication of the fact that blossoming can be very erratic from year to year.
  • When the plants do blossom, the buds open only at night and usually only partially, revealing the seed pod at the center.
  • The terminal blossom only blooms one time and then the core of the blossoms dries up and falls off.

Blossoms at the terminal end of a Joshua tree. The one on the left has partially blossomed. Sometimes the green buds never do open all the way. The pointy one at the top is all done blossoming and will fall off eventually. I don't know if it's unusual or not for one terminal end to have two blossoms on it.
(Photo by the Apple Lady)

  • For a long time, scientists thought that only one species of moth pollinated Joshua trees, but it turns out there are actually two, depending on whether the trees grow in the eastern or western part of the range. Still, that's not very many species for the plants to rely on for their propogation.
  • The yucca moths fly around at night -- which is when the blossoms are open -- collecting the pollen until they have enough collected to form a sticky ball. The female moth then forces her sticky pollen ball into a flower, fertilizing it, and also injects her eggs. When the eggs become larvae and hatch, they eat some of the seeds within the flowers. Others that they don't eat get blown away to make more trees.
  • In addition to the moths, multiple species of birds (including orioles, wrens, owls), animals (lizards, chipmunks, woodrats, snakes) and insects (moths, ants, termites), rely on the Joshua trees, making their homes on or near them or using them for food.

Native folks have found all sorts of uses for Joshua trees.
  • They used the pointy part of the spines to sew with.

Close-up of spines on Joshua tree plant. Faintly in the background is another blossom that's finished.

(Photo by the Apple Lady)

  • They smashed up the leaves to make a pulp, which they then used as soap, shampoo, or for washing clothes.
  • They sewed or wove the leaves together make sleeping mats or to make a kind of roofing material that was resilient and waterproof.
  • They roasted and ate the buds, which have a very high sugar content and taste sweet.
  • They ground up the seeds and made them into flour or ate them whole.
  • They used the roots to make a tea to treat gonorrhea.
  • Since some of the smaller root fibers are red, they wove those into their baskets for extra color, or they used the fibers to make red dye.
  • They used the cylinder-like trunks like cans to store nuts and berries.

The hollowed-out inside of an old Joshua tree stem. It felt pretty fibrous when I picked it up and part of it crumbled and broke away pretty easily. But it's so nicely circular, I can see the desire to store things in there. Also, you can see how there wouldn't be any "rings" to count like in a regular tree.
(Photo by the Apple Lady)

White folks in the late 1800s and early 1900s tried to find commercial uses for Joshua trees. They came up with various get-rich-quick schemes for the trees, but all of them were pretty much dismal failures. I read about these ideas in various print sources at the Palmdale City Library's excellent local history room, but I didn't take good enough notes so I'm a bit fuzzy on the details.
  • One guy from San Francisco thought he could sell all kinds of the wood to make paper pulp. So he had a bunch of Chinese laborers chop down acres of Joshua trees. All the wood got loaded onto ships but then either they couldn't get the OK to sail or a storm came up but anyway the wood sat on the ships and got soaked and all the wood spoiled. Thousands of trees had been cut down to no purpose.
  • Somebody else thought he could make an alcoholic drink from the roots that would taste similar to bitters. So he dug up a lot of roots to make a big batch of the beverage. But "nobody could tolerate it."
  • Because the bark of the tree absorbed moisture very easily, someone else thought the outer fibers would make terrific wallpaper. So they cut down a bunch more of the trees and experimented with various dyes and solutions. But the fibers soaked up too much moisture, and then it all dried out really fast, which made the bark shrink and it fell off of the wall to which it had been stuck. So no Joshua tree wallpaper.
  • For a while, the US government used the wood to make splints and prosthetics during World War I. But the wood turned out to be not as ideal as they'd initially thought and people preferred splints and prosethics made of other materials. So more of the wood went to waste.
  • Currently, nobody has any commercial uses for Joshua trees. In fact, the plants are now protected. If anyone wants to dig one up, they have to get permission, pay a fee, and they are required to plant the tree elsewhere. Failure to do any of this will get you a hefty fine.

(Photo by the Apple Lady)

After I hung out with the Joshua trees for a while, they started to seem very friendly. Like families of alien alpacas or something. But mainly families. Above you can see a slightly taller one and many young ones that I thought of as "children" of the older plant. I'm not the only one who sees them as people; one scientist said, "To try to describe the average Joshua tree is a little like trying to describe the average person."

It's nice to know that people are looking out for these plant families.

P.S. Yes, there's also U2's album The Joshua Tree. You can download the whole thing as an MP3 for $9.50 from Amazon.

National Park Service, Joshua Tree National Park, Joshua Trees
Mary Evelyn Austin, Joshua, My Love, 1987 -- a much better resource than it sounds
Graeme Somerville, San Francisco State University, The Biogeography of the Joshua Tree (Yucca brevifolia), Fall 1999
Geocities (soon to be extinct), Palmdale History
Desert USA, Joshua Trees
Michael Mares, Encyclopedia of Deserts, 1999, pp 315-316.
Jeremy Yoder, Joshua tree genetics suggest coevolutionary divergence,
Denim and Tweed, October 2, 2008
Sustainablog, Joshua Trees and America, January 21, 2009
UC Berkeley, Monocots versus Dicots