A month ago I blogged a piece about a caterpillar with unusual behavior. It was eventually identified as a Catocala, which pupates into the better-known underwing moth. The one I found had coloration to match the bark of an oak tree; for excellent cryptic coloration, look at this one that matches a lichen-encrusted twig.
The unusual behavior was a quite violent thrashing about, flipping upside-down to reveal what I thought were holes in its abdomen, but were just colored patches. The same behavior is mentioned here, and I've seen it described at other links.
I had thought the behavior was just a way to startle a potential predator, or to wriggle under leaf litter. Recently while reading about aposemitism, I encountered the term "Unken Reflex" and decided that must be what the caterpillar was manifesting. The Unken reflex is a defense mechanism of amphibians ("unken" is German plural for "toad"), which involves exposing a brightly-colored body part that is normally hidden. Bright colors are worldwide cross-species signals of poison and toxicity, used by prey to warn predators against unnecessary attacks. The salamanders in the two photos are displaying their orange and yellow bellies to indicate that they are unpalatable. The amphibian thus has the advantage of crypic coloration for general daily camoflage, but bright coloration for use when attacked or threatened.
I've not seen that term used in association with caterpillars, but I think that's what he was doing when I encountered him - thrashing inverted to show his color spots as a way of saying "don't eat me." It worked. I didn't.
The top photo appears to be that of a rough-skinned newt, Taricha granulosa. This is a common species in the forests of western Oregon, where I used to live, and at certain times of the year it was difficult to hike without stepping on one. (Their camouflage is extremely effective.) At such times, if the newt felt it was in danger from a klutzy hiking boot, it would indeed go into this defensive posture, closing its eyes and advertising its orange underparts.
ReplyDeleteYou might be interested to know that with this specific newt, that advertisement is not a bluff. Glands in its skin produce tetrodotoxin, more famously known as the toxin produced in the gonads of puffer fish, which are a highly prized sushi item in Japan and marketed as fugu.
There is enough tetrodotoxin in the skin of an adult rough-skinned newt to kill 25,000 mice. However, the common garter snake (Thamnophis sirtalis) is immune to it and can snack on T. granulosa with impunity.
I'm aware of one relatively recent recorded human death from consumption of a rough-skinned newt. The victim was a 29-year old male, and there was alcohol involved. Yes, he swallowed it on a dare. Goldfish are so much safer.
Most interesting. You should start a blog.
ReplyDeleteWhen I was a kid I picked up a caterpillar that subsequently started thrashing about. Scared me bad enough that I still have an irrational fear of caterpillars (that and two other unrelated incidents)
ReplyDeleteI guess it works in a few different ways!