Eastern Tiger Swallowtail butterflies are already flying along highways and open fields in the southern part of the state. They begin emerging by late February in southern Mississippi, but do not appear in north Mississippi until several weeks later. This is like the yellow blooms of Caroline jasmine, which can be spotted in February along highways in south Mississippi, but do not appear until weeks later farther north. (These are toxic by the way, so not for use as food. The nectar is even toxic to honeybees.) Mississippi includes plant hardiness zones ranging from 9a to 7b, and this temperature gradient affects insects, as well as plants.
The tiger swallowtail is one of the largest, most beautiful, and most easily recognized insects in the state, with a wingspan of up to five inches, their slow flight, and those striking black and yellow wings. One interesting quirk of this species is that they are not all yellow and black. There is also a black color phase—females only, that is easily mistaken for one of the other swallowtail species.
Tiger swallowtails spend the winter as a chrysalis, hanging from the twig of a host tree, and emerge in early spring. There are several generations per year. Hosts include tulip trees (aka yellow poplar), wild cherry and sweet bay magnolia. Sweet bay is especially common in south Mississippi, which explains the large number of tiger swallowtails that occur there. These are all large trees, which explains why the caterpillars are not often observed; they are usually just too high up in the trees to be easily seen.
The caterpillars employ several defensive strategies to help avoid being eaten by birds. Younger caterpillars resemble bird droppings, especially when they are sitting still in the daytime. Larger larvae are green or brown, which helps them to blend in with leaves and twigs. They also have two conspicuous eyespots on the front section of the body just behind the head, and this area is also swollen or enlarged, giving the caterpillar an ominous, snake-like appearance that is likely to be intimidating to hungry blue jays.
If all these devices fail, the caterpillar has one last trick. Located just behind the head is a special defensive organ known as the osmeterium. When alarmed the caterpillar may rear up and suddenly evert this osmeterium into an orange, forked structure that looks a bit like a pair of horns, and this action is accompanied by the release of a strong, unpleasant odor. The combination of those eyespots, the startling appearance of the orange “horns” and that lingering bad odor is often effective in fending off attacks by predators. All species of swallowtail butterflies have these osmeteria, but their color and odor vary with species.
Seen any tiger swallowtail butterflies yet this year? If not, just keep your eyes open; they will be showing up soon.
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service.
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