Counter-shading may keep caterpillars out of trouble
Scientists from the Universities of St Andrews and Bristol are studying caterpillars to see how counter-shading, where an animal’s upper body is darker than its lower, provides camouflage.
Because light comes mostly from above, more light usually reaches the top of a body. If an animal is uniformly coloured it therefore appears lighter on top and darker below. Counter-shading is thought to cancel out this effect, making the animal appear more uniform and hence harder to see.
But because these caterpillars spend most of their time hanging upside down beneath a twig, their top half is lighter than their bottom.
The top image shows an upside-down Tau Emperor (Aglia Tau) moth caterpillar appearing to have roughly uniform colouration, but the bottom image shows that it is actually lighter on top.
These scientists are measuring if light-colour interactions do cancel out so that the caterpillar appears uniform. They are using mathematical modelling and behavioural experiments to determine how much harder caterpillars are to spot when their orientation does, or does not match their counter-shading.
Images copyright under CC licence Olivier Penacchio
Read more: http://julieharrislab.wp.st-andrews.ac.uk/photonstoform/
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