frass expulsion

[Ron Gatrelle]

----- Original Message -----
From: "Liz Day" <beebuzz at kiva.net>
Subject: Re: frass expulsion


> >As for the projectile frass thing, could it be that the caterpillars
>  >simply want to get the frass of the leaves they're on?  Big
caterpillars
>  >would have no problem with this as their frass is heavy and drops
>  >easily, where as small caterpillars' frass does not.
>
> It could be.   It seems the few kinds of larvae I've watched, they either
> shoot the frass or they don't, from the time they're tiny until they're
> large.   As we talk about this, and the advantages of making sure your
> frass doesn't fall to rest on a nearby leaf, I'm wondering why ALL larvae
> don't shoot it out.   Saturniids just let it fall.    Even if you are
> hanging on the underside of a leaf, it might come to rest on the leaf
below
> you.  And they have plenty of parasitoids.   Mysterious.
>
> Liz
>


In reading this thread over the last several days I have been waiting for
someone with more technical knowledge to jump in - but this has not yet
happened.  This is apparently a fertile area that is wide open for study.
Two years ago at the Lepid. Soc. annual meeting in NC an individual (from
Florida I believe) gave a very interesting and informative presentation on
this subject.  The species they chose to study escapes me but I believe it
was a skipper.  They had some great photography of the mechanical structure
that flicks the frass out and away. This was a totally involuntary action.
As the frass passed out the anus a small barb like appendage was moved into
a tension position by the frass.  After the frass got so far down the
channel the barb acted like a spring and in snapping back into its position
provided thrust that flung the frass several feet away. They also
demonstrated that wasp/fly predators found larvae by detecting their frass
when nearby. Several other very interesting aspects. Some larvae are very
neat house keepers and others wallow like pigs in frass filled shelters.

Ron


 
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