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Tuesday, October 18, 2005

XO Skeletons

Bugs leave stuff behind as they enact their little lives. We call it frass. If there was human frass, it could be stuff like my four pairs of converse caked with mud, grass seeds, gromulch and dog hairs sitting in a heap on the back porch. Some frass is ridiculously easy to find, like the webs you stumble into. Some frass is distressing, like the pile of termite droppings under your picnic table. But other very cool frass, shed exoskeletons, is kind of illusive. It would seem most bugs seek a concealed spot to molt.

The exoskeleton, aka cuticle, is secreted by the bug's epidermis in an amazing process in which the inner layers of the current exoskeleton are digested and recycled into the new exoskeleton. The structure of the exoskeleton is really nifty. One interesting factoid is that it's made of chitin, which also makes up the cell walls of fungi. Hmmmm, bugs and 'shrooms . . . what is the connection? Speaking of mushrooms, my brother-in-law (not the one who resembles the candidate for congress; the other one) and his wife once had dinner with us at Claim Jumper. They both ordered the prime rib (which mushrooms remind me of), ate most of it, and then each swallowed a chitosan tablet. Chitosan is interesting stuff made of chitin, but the jury is way out on whether it prevents fat absorption. Wings, I'd say the most significant evolutionary development in insects, are part of the exoskeleton, which enables flight without sacrificing a set of limbs. The same might be said for mushrooms, and also flying would burn a lot of calories, so it's all connected in a vague sort of way.

One thing the exoskeleton can't do is grow. Young insects'--larvae and nymphs--function is to grow so molt they must in an exquisite paradox: the insect (or spider) must shed its efficient protective layer to emerge as a larger version of its former self. The new covering takes a while to cure, and during this period the insect is pale, soft and vulnerable. Kind of like my feet when I kick off those tennies, although there the vulnerability would lie mostly in the nose of the beholder, not the feet. That must be why the molting creatures seek a hiding spot in which to complete the process. This process is repeated a number of times until the insect matures. Then, their mission is to disperse, mate and procreate. You'll never see frass with wings.

Some exoskeletons have color, but most I've found are pale and transparent. As species with incomplete me
tamorphosis (like stink bugs) grow, the color patterns in the instars change. The pigments must reside in the two inner layers (the procuticle) which are then reabsorbed and reorganized at each molt. Some insects and spiders change color in response to environmental conditions. What process accomplishes chemical change in the non-living cuticle?

Thanks to the entomology pages by John R. Meyer at NC State University for the info on morphogenesis.


Cindy said...

Hey, I always thought frass only meant poop. It means shed skin, too? I just learned something.

I am finding that we nature loving photo-bloggers are intreagued and inspired by a lot of the same things, and it puts a touch of deja vu in our blogs. For example, when I saw your grasshopper shedskin, I could have sworn I took one exactly like it! So I went into my archive, and sure enough I found one very similar, same size, lying on a bed of dead leaves, only mine was facing in the opposite direction. (and yours was more sharply focused than mine)
As I discover more of these nature and bug themed blogs, I am seeing it more and more. And, no, I'm not comlpaining about it. I actually think it's kind of cool when I realize that other people are getting the same kick out of the same stuff as I am.

womble said...

I love your blog. The pictures are particularly amazing but also the way you describe things is interesting, well written, informative and not patronising yet not too high brow. I did my degree in Life Sciences so have an interest in these kinds of things.

Keep on doing it, please!

Robin said...

I love reading your blog--I find joy and grace in the details and am glad I tripped over your writings. I love bugs. Probably too much.
We just had a huge crop of leag legged bugs invade the cedars here for a few days. It was simply amazing--hit a limb and it's The Birds all over again. The boys across the street screamed like girls when they found them and were sure they were wasps and deadly and meant to be killed. I called them over and showed them the bugs were harmless and what they looked like. One had it in his head to flick a cluster of them and I told him if he did he'd be sorry--we don't kill things in my yard. He thought I was joking but the others told him I wasn't.
Thanks for all of the information you provide and your stories!

vanessa cardui said...

"Frass is insect debris" so says Bug Guide. I too think of frass in a liberal way; kind of like the items all over my daughter's bedroom floor might be referred to as "shit" by others less cultured than me. I do not consider dead insects as frass; but rather as dead insects.