A Hornworm of Another Colour

In August of 2003 I discovered this critter and some friends on garden tomato plants. I grabbed this photo but was unable to find out what this was until this past weekend. I posted the photo on BugGuide.net and within the hour I had the answer. It looks so much like a tomato hornworm because it is.

A later blog search turned up a post at Pharyngula from last February that mentions this phenomenon: Evolution of a Polyphenism. Apparently the colour variation is a result of temperature during the early stages of development--not sure if it's during the egg stage or what. Anyway, cooler temperatures result in this black form; warmer, green. I checked the weather records for the summer of 2003 and found that while it was a fairly moderate summer (as compared with, say, 2005), and there were some cool nights in July (10C), nothing jumped out as a protracted chilly spell.

Tomato Hornworm (Manduca quinquemaculata), dark morph.