Word of the day: Frass
(The word of the day is a random word on a random page of the Torre-Bueno Glossary of Entomology)
Frass, solid larval insect excrement; plant fragments made by a wood-boring insect, usually mixed with excrement.
We deal with a lot of frass around here.
Caterpillars are eating machines… which means they are also pooping machines.
I just realized I don’t have any good photos of frass, but here you can see the pile left behind by some Acronicta americana caterpillars.
Luckily for us, caterpillar frass is usually fairly innocuous – it is dry, doesn’t smell, and is composed of vegetative matter. Kind of like my rabbit’s droppings. Unfortunately, unlike my rabbit, caterpillars cannot be litter trained. So we spend lots of time cleaning out our rearing containers.
Some other frass stories:
While cleaning the lab sometime last year, we came across a frass collection. No joke. Little tiny boxes (perhaps meant to hold rings or earrings) were opened up to reveal giant pieces of frass from saturniid caterpillars, ziploc baggies full of frass, boxes of frass that rattled like maracas. I’m not sure if we got a real explanation as to whose they were or why they were collected… or where they disappeared to after we found them.
And did you know that some caterpillars fling their frass? It sounds silly at first but it makes sense. Some parasitoids (like wasps) will find their prey by following the scent of frass. So if you ditch the frass, you are ditching the evidence of your presence.
Some caterpillars will grab it and throw it. Some can really fling it far, while others give more half-hearted attempts. Like this little Acronicta afflicta I filmed last year.
Another way, that requires less effort, is to fling the frass with a built-in anal comb. Let me tell you, I was afraid to google that. Here is a picture (from omafra.gov):
Basically those spines are used to eject the frass at high speed. I will try to get videos of this if we raise any frass-flingers in the lab this summer. I remember last year we had a heck of a time cleaning some caterpillar containers because the sides were coated in frass, instead of it just dropping to the bottom.
Some lab hilarity from last year:
Speaking of frass, I have some caterpillars to attend to.