frass expulsion

[Liz Day]

The furcula (notodontid moth) larvae are full grown and some have 
cocooned.   I haven't been able to get any formic acid out of them, but 
maybe I didn't squeeze them right.

Anyway, I notice that they forcibly expel their frass from their butts like 
a popgun so that it goes some distance from them.   Sulfur butterfly 
caterpillars do this, and I was told it was an adaptation to get the poop 
away from the larva so its odor wouldn't attract parasitoids.  This made 
sense since the sulfur lives on a low-growing plant (alfalfa), so if the 
poop just fell it would be very near the larva.   But the furcula live in 
cherry trees, so they are already 10-50 feet above the ground.  It seems 
odd that such an adaptation would be useful or needed in this 
situation.  The saturniids I've raised just let their frass fall, and I 
assumed this had to do with them being arboreal.

Do most caterpillars shoot their frass out like this?   I haven't reared 
that many different kinds.   Is there some other possible explanation 
besides parasite avoidance?

Liz

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Liz Day
Indianapolis, Indiana, central USA  (40 N, ~86 W)
Home of budgerigar Tweeter and the beautiful pink inchworm (Eupithecia 
miserulata).
USDA zone 5b.  Winters ~20F, summers ~85F.  Formerly temperate deciduous 
forest.
daylight at kiva.net
www.kiva.net/~daylight
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