Carpenterworm Moth

Prionoxystus robiniae

August 22, 2003

A new family added to the site - Cossidae.

At first glance, the moths in this group may resemble sphinx moths.  They are medium to large in size, have long wings and heavy bodies with the abdomen protruding past the wings.  Like the ghost moths, who I think also bear a resemblance to this family,  the venation of the wings are simple and primitive.  There is not much color to them, either, and their wings are various shades of browns, grays and whites.  There is often dark mottling or webbing across the surface, giving them the appearance of an old, decaying leaf.  When flying, their bodies seem a bit heavy for them.  Their use of the gift of flight is not one that inspires envy.

Our best known cossidae is a species that most of us have only seen dead.  Some, have boasted about the experience of eating one.  The species name is Comadia redtenbacheri, and it is best known as the "worm" in the bottom of a bottle of mescal.  Its common name is Agave Worm.  The larva feeds on the agave plant and apparently adds a certain flavor to this Mexican elixir.  Its introduction to this drink began as a test.  The worm would be dropped into the mescal, alive.  If it was still wriggling by the time it reached the bottom, the spirits were safe to drink.  It was in effect, a canary in a coal mine.

Incidentally, you will never find this larva in the bottom of an authentic bottle of tequila, which is only produced in the Mexican town of Tequila.  It is a similar, but different drink often confused with mescal.

The larvae of the moth pictured here are what lend this group the name of carpenterworm.  The caterpillars, which can grow up to two and a half inches long,  bore into the wood of living deciduous trees.  Because the wood they eat is not high in nutrients, many of the species take an extra couple years to develop.  The larvae don't smell very good and at some point in their history with humans have had their aroma likened to that of a goat, hence their other common name of goat moth.  I don't know what a goat smells like, but next time I come across a carpenterworm, I may will sniff one and find out.  

When they are ready to pupate, the pupae work themselves to the entrance of the hole.  They can be found protruding from those holes in summer.