Swallowtail caterpillars are able to extend a brightly-colored, Y-shaped horn (called an "osmeterium") from behind their heads when they are disturbed. These horns are able to secrete foul-smelling defensive chemicals. The last two photos are ones I clipped from a video we got of it extending its horns at us.
Spotted in Kennesaw Mountain National Battlefield.
Lat: 33.98, Long: -84.58
Spotted on Jul 9, 2011
Submitted on Sep 8, 2011
and 1 other person favorited this spotting