Wednesday, December 10, 2014

Frass Flinging Caterpillars

Silver-spotted skipper caterpillar with brown head - Chris Barnhart
As I am a retired gastroenterologist, Chris Barnhart knew he could hook me with this video of his showing a caterpillar shooting out its frass. Many animals have special ways of eliminating their fecal matter, called frass when produced by insects, to reduce disease or avoid predators.  Epargyreus caterpillars simply go ballistic.

http://upload.wikimedia.org/wikipedia/commons/9/99/Silver-spotted_Skipper_Epargyreus_clarus_Milkweed.jpg
Silver-spotted skipper - Wikimedia
The common Epargyreus species we see in Missouri is the silver-spotted skipper, Epargyreus clarus. They are regularly found throughout the warm months nectaring on a wide variety of flowers. Its caterpillars feed on a wide variety of plants in the pea family, ranging from the beggar's ticks (tick trefoil) that cling to your clothes to the black locust tree that can exceed 100 feet tall.

Cocked and ready to fire
Our silver-spotted skipper can use its anal comb to shoot its frass "faster than a scat out of hell," to quote Chris. It can fly up to an astounding 38 body lengths away. (Yes, some one actually has measured its record launch - and you thought filming it was odd). It is not alone in long-range bombing. There are videos on line of frass-flinging Asian caterpillars like these of Mycalesis mineus, Ypthima pandocus and.....oh well, you get the picture. 

Frass flinging is commonly found among caterpillars that live in leaf nests. Why do they bother? This is felt to be a defensive mechanism to eliminate the smell in the nest which would be a clue to predators, specifically the northern paper wasp, Polistes fuscatus as described in this study.

More stories of scat disposal and frass chain building caterpillars in future blogs.

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