A superstar, an instar, a super suffocated interinstar,

August 30, 2011 8:53 PM

Why caterpillars molt. The lifecycle of the lepidopteran, from egg to caterpillar to winged butterfly or moth has long been a basic lesson plan of "hands on" biology in grade school classes. If one focuses on a single lifestage of this grand cycle, however, one sees that the caterpillar, after emerging from embryogenesis quite small, goes through several stages, or instars, becoming more grand at each shedding of the skin, until at last the massive beast pupates. So what triggers these transitions within the caterpillar? Recent research suggests a process triggered by suffocation by bulk.

In short, the low oxygen, induced by constriction of the passive flow through the respiratory trachea of the caterpillar drives each successive molt up to pupation. The constriction is caused, of course, by the hungry hungry caterpillar eating anything in sight.

posted by Cold Lurkey (21 comments total)

Hmm, I wonder if you could make the caterpillars even larger by putting them in an oxygen rich environment.
posted by delmoi at 9:06 PM on August 30, 2011 [1 favorite]

That may be why there were such giant insects in the oxygen rich periods. Like the cambrian (paleontologist's help please?).
posted by Cold Lurkey at 9:14 PM on August 30, 2011

Hmm, I wonder if you could make the caterpillars even larger by putting them in an oxygen rich environment.

Yeah! Get a set of identical twin miniature girls and let's DO this!
posted by The otter lady at 9:23 PM on August 30, 2011 [3 favorites]

For some reason that makes no sense, all of the words in this post give me the shivery heebie-jeebies.
posted by rhizome at 9:30 PM on August 30, 2011 [2 favorites]

An article about hornworm size published in the journal PNAS.

Somebody lost a bet.
posted by dephlogisticated at 9:53 PM on August 30, 2011 [3 favorites]

Bigger on the inside? No. Basic miniaturization sustained by a compression field. Oo! Watch what you eat. It'll get you every time.
posted by dhartung at 10:17 PM on August 30, 2011

Hmm, I wonder if you could make the caterpillars even larger by putting them in an oxygen rich environment.

The last link discusses this; they can get very slightly larger caterpillars with extra oxygen, and the effect is more noticeable with earlier instars than with later ones, but it's a minor change.
posted by Malor at 10:22 PM on August 30, 2011

Not clicking a single link. Figures my one real phobia shows up on the blue. Can't sleep... giant caterpillars coming to get me.
posted by KingEdRa at 10:36 PM on August 30, 2011

Fuck caterpillars.
posted by ryanrs at 11:56 PM on August 30, 2011 [2 favorites]

The new study also tested whether the caterpillars could molt after being decapitated.

I hope they're re-using all those perfectly good decapitated caterpillar heads. My tax dollars are paying for this!


Interesting stuff though. On a tangentially related note, I was blown away recently when I was visiting my grandmother and she spotted a luna moth outside, casually noting that these things have no mouths! After emerging in winged adult form, they just fly around starving for a week until they die. Bugs are crazy!
posted by p3t3 at 12:01 AM on August 31, 2011

I spent a great morning with the kids at a butterfly farm on Sunday. I'd recommend it to any parent of small children. Their reaction when the butterflies flew up and landed on their outstretched hands (presumably for the salt or something) was really something special to see.

Just as we were leaving I went to brush aside a big leaf that was dangling in front of me, only to realise it was an Atlas moth. It was a good ten inches across. I'm so glad those things don't have teeth and a taste for human blood.
posted by le morte de bea arthur at 1:45 AM on August 31, 2011 [1 favorite]

That may be why there were such giant insects in the oxygen rich periods. Like the cambrian (paleontologist's help please?).

IANAP (Geologist instead), but you're probably thinking the Carboniferous (late Pennsylvanian if you're American). Meganeura was late Carboniferous dragonfly that had a >2 foot wingspan. Insects weren't around until the Devonian.

The concept that insects were bigger based on increased atmospheric oxygen isn't new - the article about Meganeura cites a paper from 1919 that proposes the same thing. (Given their 'primitive' respiratory system, it's not a big leap). The idea that oxygen starvation is a trigger for moulting is interesting...why not put them in an oxygen-starved situation and see what happens? Can you trigger premature moulting and/or pupation?
posted by grajohnt at 2:59 AM on August 31, 2011

The idea that oxygen starvation is a trigger for moulting is interesting...why not put them in an oxygen-starved situation and see what happens? Can you trigger premature moulting and/or pupation?

That's exactly what they did. It's all in that last link.
posted by Malor at 5:04 AM on August 31, 2011

I have lots of practice skimming papers and missing the point, so there's no surprise there...
posted by grajohnt at 5:16 AM on August 31, 2011

All I need is a spiracle.
All I need is O2.
posted by plinth at 5:45 AM on August 31, 2011 [4 favorites]

Hmm, I wonder if you could make the caterpillars even larger by putting them in an oxygen rich environment.

One word: Mothra
posted by stormpooper at 5:47 AM on August 31, 2011

My mind is blown everytime I think of the amazing capabilities of life on earth. I mean this thing changes completely into something entirely new. Its like me going to sleep one night and waking up as a bird type thing the next morning.
posted by amazingstill at 6:07 AM on August 31, 2011 [2 favorites]

Fuck caterpillars.

To each his own.
posted by y2karl at 8:11 AM on August 31, 2011 [2 favorites]

The US, in conjunction with Wal*Mart, is currently engaged in a national-scale research project to determine at what point oxygen starvation causes humans to molt. So far we have not yet found the upper limit for our first instar, but efforts continue.
posted by rusty at 8:49 AM on August 31, 2011

"The Hungry, Hungry Caterpillar" now has somewhat horrifying subtexts.
posted by Slackermagee at 9:40 AM on August 31, 2011

Figures my one real phobia shows up on the blue.
Metafilter has introduced me to phobias I'd never even considered before, like trypophobia, and shown visceral-for-the-internet grade reactions to spiders and other creepy crawly type things that are substrates for relatively commonplace aversions. That's made me more sensitized and wary of pointing to images that may create issues for phobic persons. That said, I've never heard of a caterpillar phobia before. I'm sorry that I've so thoughtlessly put forth a tremendous trigger for you and rhizome, but in honesty, there was no idea that someone would be so adverse to 'pillars. My apologies.
posted by Cold Lurkey at 9:11 PM on August 31, 2011