Cryptic Caterpillars

In the interests of my own personal goals to post at least once a month, I’m going to re-publish my very first post on my first iteration of the Norfolk naturalist blog, which was on tumblr. I’m planning to re-post all of my articles that I wrote on my tumblr on this site at some stage (possibly with some slight updates/alterations) since I would like them all in one place, and my own website seems like the best place to have that. So here is my first Norfolk Naturalist post, originally published on my tumblr back in 2018 (over 4 years ago!):

While walking the trail near my house, I spotted a twig in an unlikely spot. Instead of forming the final split of a growing or dead branch, the tiny twiglet (just larger than my fingernail) was jutting out into the air from the railing of the bridge. Something strange was going on. On closer inspection, it turned out not to be a twig at all. Rather, a caterpillar had chosen a poor and rather conspicuous spot to hide.

If this caterpillar had chosen a better location, it surely would have fooled me. Even where it was, it was extremely difficult to spot. The coloration and shape of its back was a perfectly mottled gray-brown, and its posture was that of a twig. It was thin-bodied and elongate, only about a millimeter around.

The caterpillar’s odd shape is provided by it having a large space between what are its true legs (the six legs just behind the head) and its ‘prolegs’ which are fleshy stubs coming off of its abdomen. This large space also causes these caterpillars to move in a unique fashion. They lift the front group of legs and extend it forward, reaching ahead and securing themselves there. Then they lift their rear group of legs and move them forward to reconnect with the front legs. Once together, the rear legs hold their place and the caterpillar once more reaches forward with its front legs. This “inching along” process provides this group of caterpillars with their name: the Inchworms (Family Geometridae).

A caterpillar’s main predators are birds which hunt visually. If the caterpillar appears to be something other than a morsel to a hungry bird, then it has succeeded and survived another moment. This type of behavior has a technical name: “crypsis” or “cryptic behavior”, which just sounds amazing. It strikes this cryptic pose when threatened, and so effectively disappears from a hunting bird’s search. I suppose it must have assumed this position when I walked near, thinking me to be hunting it for food. In reality, I was hunting only for a few pictures.

I hope you enjoyed that “repost” from the older version of norfolk naturalist blogging. I promise I’m still working on My Top 20 Nature Photos of 2013-2020 series and I also have several other posts about more recent nature sightings in the works. Hopefully April will be a more productive writing month!