Spot the Caterpillar!

We get a steady stream of people bringing things in jam-jars for identification in Biol. Sciences at Durham University and yesterday a gentleman called Mr. Clark from Sherburn Hill brought in this little beauty - one of the finest examples of crypsis I've seen in a long time. I promised I'd try to identify it for him, which will probably mean keeping it alive until it completes its transformation into a mature moth, so for now it's simply a geometrid moth caterpillar (aka looper caterpillar, aka inchworm). If there are any moth experts out there who can put a more precise name to it I'd be very grateful....

This is the front end, with a tiny head and legs tucked up underneath ....

..... and here's a head-on view

Here it has adopted a 'broken twig' pose. Looking like a dead twig is only half the battle if you are trying to avoid being caught by a blue tit and fed to its hungry nestlings - you need to behave like a dead twig too, and this caterpillar can hold this pose for hours. The secret of how it manages this is in the photo at the bottom of this post

Under a low-power dissecting microscope you can see how small the head is, resembling the broken end of a twig...

.... and in side view you can see a row of simple eyes (ocelli) that must allow it to detect movement when its head is tucked into the overhanging hood. You have to look really hard to spot the three pairs of legs, tucked up tightly underneath (double-click all these images for a larger, clearer view)

The resemblance between the body and a dead twig is uncany, right down to 'knobbly bits' that resemble scars on a twig.

Here's the tail end, with a pair of claspers that cling tightly to the supporting twig. The two pale, oval structures on the side of the body segments are spiracles, that lead to trachea that conduct air into the animal 

And here's how it manages to hold that pose for so long, by suspending the head end with a single silken thread.

For more on looper caterpillars, click here.