I’ve noticed that immediately after they are killed, wasps (yellowjackets) appear much smaller and somewhat less brightly-coloured than they did while alive. This seems to be the case regardless of how they are killed.
Is this just a trick of perception or is it a real phenomenon (and if so, what causes it?).
Well, when the wings are moving, it creates an illusion of space that is “occupied” by the wings and belonging to the wasp. Therefore when it is dead this space is decreased. Plus they curl up a bit.
As far as the color, I don’t know much about wasps, but they must have some sort of circulatory system, in which case the decrease in color can be attributed to the decrease in fluid motion, just as in dead humans.
I’m sure there’s something in what you say, but I’m primarily thinking about the (perceived)size of the insect’s body :-
wasp crawling on my jam sandwich = plump and bright
same wasp lying dead = much smaller and dull (even taking into consideration the curling up).
I don’t think insects have a very complex circulatory system, but I seem to recall that certain iridescent beetles lose their sheen within a few hours of death - I had always assumed that the exoskeleton of an insect was not composed of living cells (like our toenails and hair), but maybe that’s not the case.
<WAG>
Could it be that the irridescense of the buzzing wings mentioned above also give a lustre of reflected/refracted/resomethinged light when the body of the wasp is viewed through them?
</WAG>
Driving home from my holiday, I had a flash of brilliance; the abdomen of the wasp is composed of a number of overlapping rings which are to a degree telescopic; each of the rings carries one black and one yellow band in the same order on each; if the size of the creature decreases by means of the rings overlapping a little more, then a small area of the same colour is hidden on each ring along the whole abdomen. I was expecting to find that it is the yellow band that is hidden, but it’s the black one. Still this might be part of the answer; the wasps would become less ‘contrasty’ rather than less coloured.