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Saturday - September 29, 2007

From: Houston, TX
Region: Southwest
Topic: Wildlife Gardens
Title: Caterpillars on Carolina buckthorn (Frangula caroliniana)
Answered by: Nan Hampton

QUESTION:

I have a Carolina buckthorn and last year there were interesting looking caterpillars munching on the leaves. They were camouflaged to look a bit like bird droppings. The plant database makes no mention of Carolina buckthorn as being a larval host. What species of caterpillars might they be?

ANSWER:

Mr. Smarty Plants found Carolina buckthorn (Frangula caroliniana—synonym=Rhamnus caroliniana) listed as a host plant for caterpillars of gray hairstreak (Strymon melinus), spring azure (Celastrina ladon), and painted lady (Vanessa cardui) in Caterpillar Food Plants for Central Texas compiled by Mike Quinn, Invertebrate Biologist, at Texas Parks and Wildlife Department. Unfortunately, none of these caterpillars look very much like bird droppings. Another source identified caterpillars of Henry's elfin (Callophrys henrici) feeding on Carolina buckthorn. Again, it would be a stretch of the imagination to confuse these larvae with bird droppings.

At this point, Mr. SP decided it was time to contact the butterfly/caterpillar expert, Mike Quinn, for further insight. He offered a few more caterpillars of Texas butterflies that feed on plants of the genus Rhamnus, but not specifically on Rhamnus caroliniana (=Frangula caroliniana):

Spilosoma vestalis (Family Arctiidae)

Itame guenearia (Family Geometridae)

Pero macdunnoughi (Family Geometridae)

Triphosa californiata (Family Geometridae)

Cnidocampa flavescens (Family Limacodidae)

Celastrina argiolus (Family Lycaenidae)

And, as Mike says: "Arctiids are hairy, geometrids are inchworms, limacodids are generally
bizarre, and lycaenids are slug-like. None in my opinion are particularly bird-dropping like."

Mike pointed out that the classic bird-dropping larvae are those of the swallowtails. The only swallowtail reported to host on plants of the genus Rhamnus is the pale swallowtail (Papilio eurymedon) and it doesn't occur in Texas.

Nick Grishin, a professor at Southwestern Medical Center, suggested your larvae could possibly be sawfly larvae and not butterflies or moths at all. Sawflies are a group of insects in the order Hymenoptera, the same order that contains bees and wasps. Sawfly larvae do resemble butterfly and moth caterpillars and although there is no specific reference to any of them feeding on Carolina buckthorn or other species in the genus Rhamnus, they do feed on shrubs and trees and a few might be said to look a little like bird droppings.

So, these are some possibilities. If none of these looks like "your" larvae, perhaps you will see them again next year and can photograph them to send to Mr. SP for possible identification.