Backyard Nature Guide: The Tiger In Your Yard

by Marjorie Rachlin

A yellow butterfly with black hatchmarks flutters into the backyard, circles the garden, and lands on the purple blossom of the butterfly bush. Several years ago I planted this bush just to attract this eastern tiger swallowtail. It will put a long straw-like tongue into the flower, sipping nectar, and sit a few minutes fluttering its wings to maintain balance. Sometimes one moves around the bush for half an hour, with occasional flights to look at other blooms.

You don’t have to garden to see this butterfly – it’s fairly common in our neighborhood in the summer, even on the flower beds along Connecticut Avenue. The black markings on the yellow are supposed to make you think of a tiger, which explains the name.

Males are yellow; females may be yellow or black. All of them have the little “tail” coming out of each hind wing. They’re pretty, but, more important, swallowtails are important pollinators for some plants. They pick up pollen on their bodies and legs and transfer it to the next flower, just like bees.

Although their main food is nectar, their main job is to mate. The males are on patrol. To attract a female, they emit a pheromone, a chemical that acts as a sexy butterfly perfume. Occasionally I see two butterflies suddenly spiral high up into the air together, then disappear and presumably mate.

Once mated, the female gets down to business. She has to find the right food plant before she can lay eggs. Like all butterfly caterpillars, the caterpillars of a tiger swallowtail are fussy – they will eat the leaves of only a few kinds of plants. It’s an interesting comment on evolution that caterpillars of each species of butterfly have their own food plants and will die if they cannot find enough of them. For example, if you see little holes on the leaves of your violets, you may have fritillary caterpillars – that’s all they eat.

In this area yellow swallowtails are looking for a tulip tree, of which there are plenty here, or a wild black cherry tree. The female does not need a Field Guide – she uses sight and smell to find the proper tree – chemo-receptors in her antenna and on the bottom of her legs are her “nose.” She lays a tiny egg on a leaf, then moves on.

The caterpillars are only 1/16 inch when they hatch a few days later, but they are big eaters – chomping tulip tree leaves steadily for about two weeks. As the picture (below, left) shows, they look like something out of a sci-fi movie. I think they are cute – although at one stage they are brown and resemble a bird’s dropping (below, right), in order to fool predators.

Growing fast, their outer skin tightens, and they have to molt out of it 5 times. When they are about 2 inches long, hormones make them stop eating and secrete a different tough outer skin. This is their chrysalis or “cocoon.” They attach it to a twig or the bark of a tree with threads of silk.

Now they are about to metamorphose into a butterfly. We’ve all heard about it in school, but when you stop to think, it is AMAZING what is happening inside that chrysalis. The caterpillar’s DNA begins a process that makes the caterpillar body disappear and then gradually produces new cells that change and develop and become the wings and body of a butterfly.

After nine or ten days, the butterfly is fully formed inside the chrysalis. It breaks out, and the swallowtail emerges with wings folded. It will sit several hours pumping fluid into its wings until they are ready to fly. At this point it begins looking for nectar and the whole cycle starts over again – egg, caterpillar, chrysalis, adult.

In our area this butterfly will usually have two to three broods, and the last one will hibernate over the winter in its chrysalis.

There are three other species of swallowtails that you may see in our neighborhood, all of them black, but they are not common. In my garden I can expect to see a total of maybe 18 different species of butterfly during the year, some more common in the spring, others in the summer. In the countryside there would be many more.

Swallowtails are not “endangered”, but there are 20 other species of butterflies and moths now federally-listed as endangered. Two of our American butterflies are already extinct. Development — roads, houses, malls — often destroys fields, swamps and other butterfly habitat, as does some farming and overgrazing. When a wildflower nectar source or a food plant disappears, so does the butterfly.

A simple guide to identifying butterflies is Stokes Beginners’ Guide to Butterflies. The “bible” for serious watchers is Butterflies Through Binoculars: The East by Jeffrey Glassberg, who is the founder of the North American Butterfly Association (NABA) You might also want to go on YouTube and browse the videos, which are fascinating.