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White caterpillar with yellow-and-black markings feeding on fennel. My daughter discovered that when you squeeze it, what look like yellowish-orange horns emerge from its head. She has a good sense of smell and says they emit a scent when they emerge. We found out these are a defense mechanism specific to Swallowtail larvae, and they are called "osmetrium." According to Wikipedia, "This organ emits smelly compounds believed to be pheromones."
A fennel plant in our yard.
Spotted on Jul 1, 2010
Submitted on Jul 10, 2011
and 1 other person favorited this spotting