Starr County Butterflies
9-29-08, eggs
10-1-08, one day old
10-2-08, joined by more recent hatchlings
10-6-08
10-9-08
10-11-08, resting
10-16-08, showing osmeterium
10-14-08, full-grown caterpillar
10-18-08, beginning pupation
10-20-08, chrysalis
Fresh Pipevine Swallowtail, 3-19-09
The native host for Pipevine Swallowtails in this area is Swanflower, Aristolochia erecta. This pipevine is a very low, slow-growing plant that occurs in grassy areas; it has leaves similar to grass blades, making it difficult to find. Sometimes the best way to find the hostplant is to watch female swallowtails as they move about an open field. When they give attention to a particular area, or begin ovipositing, then it is easier to locate the plant.
The swallowtail caterpillars, by the time they are half grown, generally defoliate the hostplant they emerge on. They then go wandering about looking for more food. It appears to me that food is the limiting factor for the population growth of this species, for often virtually every leaf of every plant I have ever located is consumed by the time a brood is raised. It has been very frustrating trying to photograph a life history of this common caterpillar: several times I have begun a study, but about the time the caterpillar I'm raising is two-thirds grown, I cannot find any more food and I have to turn it loose to fend for itself in a field where I know Swanflower grows. (I once purchased a cultivated pipevine, exact species unknown, just to raise caterpillars, but they refused to eat that particular plant!)
I finally moved a plant to my garden and covered it with mesh to keep females from laying on it. This enabled me to raise the caterpillar featured on this page. Larger Pipevine Swallowtail caterpillars like to crawl up a stem or similar object to rest after feeding; this is what the caterpillar is doing in the 10-11 picture.
I normally expect adults to emerge within a couple weeks of pupating. This caterpillar, however, "overwintered." It emerged 5 months after pupating. The chrysalis was kept on my porch. The adult was slightly deformed, as can be seen in the picture. Perhaps it was the long incubation period, or perhaps the conditions were not just right for the development of the butterfly.