When you don’t use pesticides in your garden some very interesting things will show up in it. The orange furry caterpillar feeding on leaves of pigweed is the larva of the Virginia Tiger Moth (Spilosoma virginica) a relative of the Woolly Bear (Pyrrharcticia isabella). This caterpillar is in its final instar and has taken on a red-orange coloration. Younger stages are yellow and are called “Yellow Bears”.
I photographed this Yellow Bear one afternoon two summers ago in late August. Not being an entomologist and having only the most basic knowledge of insects it has taken me a while to figure out what species this caterpillar might be. On a hunch I supposed it to be one of the Woolly Bears, a diverse moth family called Arctiidae. I’m pretty sure I got it right.
“Larval coloration is exceedingly variable, ranging from pale yellow to frosty, orange, to red. The soft setae, of many lengths, will distinguish most caterpillars. Look for the long setae (one per tubercle) extending from the thoracic and posterior abdominal segments. Middle instars tend to be yellow (the larva is widely known as the Yellow Bear). Most final instar caterpillars have some degree of orange or red coloration.”
Nagle and Wagner (2009)
The Virginian Tiger Moth is a species widespread across eastern North America from Canada south to Texas and Florida. Its larvae, like almost all Arctiidae, feed on many kinds of plants so in a sense they are grazers. The caterpillar in the photos is feeding on a giant pigweed (Chenopodium gigantea) but I have seen others of this species on blazing star (Liatris).
In northern areas there are two broods of Yellow Bear caterpillars each summer. The last brood pupates in the fall and overwinters in that stage. When spring arrives they emerge as adults with pearly white wings and white abdomens ornamented with black and yellow markings. The moths fly at night and are attracted to lights.
Nagle, Raymond B. and Wagner, David L. “Sample Species Illustrating Diversity Within the Arctiidae” in Conner, William E., editor (2009). Tiger Moths and Woolly Bears. Behavior, Ecology, and Evolution of the Arctiidae. Oxford University Press, New York, New York.