Tuesday, July 31, 2012

Monster of the dill

What: Last night I spotted a black swallowtail caterpillar (Papilio polyxenes) on our dill. When I came back this morning it was still there, perched on the same delicate pedicel (fancy name for the stalk that connects a flower to the main stem of the plant) of the dill's umbel (fancy name for an inflorescence [fancy name for a cluster of flowers connected by a central stalk to the main stem of the plant] where the flower stalks are of equal length and extend from a central point).

Prolegs on left, 6 legs on right
Ecological notes: I read two things about these caterpillars. The first is that they can decimate a patch of dill when their populations erupt, and they often do, in near biblical proportions (exaggeration, but warranted for gardeners with an affection for dill; in the photo to the right you can see all the "missing" flowers at the tips of the pedicels from where the munchkin gnawed them off). Many of their would be control-mechanisms, like birds, are thwarted by what's called an osmeterium, a weird little forked appendage at the front of the thorax (just behind the head). When provoked the caterpillar will rear up dramatically on its prolegs extend the osmeterium and emit a most rank and foul odor. Well, I had to test this out myself. I didn't smell anything except freshly cut dill (you can see a bunch of flowerless stalks that the caterpillar had nipped off), but what a beautiful treat! Perhaps the vibrant orange signals as a warning before emitting the odor, much like a skunk stomps its feet, chatters its teeth, and does a handstand before finally spraying an approaching predator.

Where: My backyard

Etymology notes: The root "osme" comes from the Greek ὀσμή, or "to smell" and the suffix "-rium/-ria" indicates a place or building (e.g. atrium, cafeteria, solarium).

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