Excerpts from Jim Conrad's
from the July 28, 2013 Newsletter issued from the Frio Canyon Nature Education Center in the valley of the Dry Frio River in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau, USA
SUNFLOWER PATCH, THE CATERPILLAR
Each morning I bike into the valley to water plants at the red cabin where I lived last winter. One job there is watering a row of ornamental sunflowers planted along a fence. This week a certain little black caterpillar species began eating the sunflowers' leaves, as shown above.
Volunteer identifier Bea in Ontario quickly pegged the caterpillar as that of the butterfly known as the Bordered Patch, Chlosyne lacinia. Bordered Patches are common here. Our "Butterflies of Uvalde County" picture of it resides at http://www.backyardnature.net/n/a/uvalde/005.jpg.
The "Butterflies and Moths of North America" webpage for this species describes the caterpillars as feeding on plants in the Composite or Sunflower Family, which among our wildflowers and weeds by far is the most represented of all plant families, so Bordered Patch butterflies should feel very much at home here, and are to be expected on sunflowers. In fact, another common name for the species is Sunflower Patch.
Bordered Patches are mostly a tropical and subtropical species, occurring from Argentina north through Mexico to southern California, casually to Colorado, Nebraska, and Kansas, and rarely even to western Missouri. Being found over such a large area, there's much variation in the caterpillar's appearance, from mostly orange with black spines, like ours, to black with a red-orange back stripe, to almost completely black. All variations have a red-orange head, though.
Neighbor Phred says that masses of little black caterpillars have been eating his sunflowers. I'm guessing that he has Bordered Patch caterpillars, for it's known that small, recently hatched Bordered Patch caterpillars are gregarious but when they grow larger they become solitary, like ours. I read that in southern Texas broods of Bordered Patch caterpillars may be produced throughout the year, and that during hot weather they may "aestivate," which is a state of reduced growth and development in response to heat and/or dryness, similar to winter hibernation.