This is the not-so-pretty larva of the Giant Swallowtail. Its coloration and patterning make it resemble bird droppings. By mimicking something unpalatable the caterpillar avoids being eaten! This caterpillar is head down on the tangerine stem. Notice the shape of its head: some sources say it looks like a small snake. This is another way the caterpillar avoids predation. Robert Benson Photo.
The Ugly Duckling of the Butterfly World
What had happened to our baby tangerine trees? Suddenly, half of them had become thin, green twigs. Where had their leaves gone?
Worried, I looked over the 30 or so tangerine seedlings we had raised from seeds gathered from a Chainsaw Tangerine Tree. And there on the bare stems were two big gray and white blobs.
It took me a moment to figure out what these blobs were. They looked like large droppings of bird poop. When I realized that the blobs were really too large for the average bird (these droppings could have been deposited by a chicken-sized bird), I remembered once seeing photos of caterpillars that mimicked bird droppings.
But what kind of butterfly would these rather ugly caterpillars become? I looked through the moth section of my butterfly guide—surely such big, gross caterpillars would become plain, greyish moths, not beautiful butterflies! But I was wrong.
After paging through the field guide I finally found a caterpillar picture that resembled these caterpillars. And it was on the swallowtail butterflies page. Not only were these caterpillars the larvae of a species of swallowtail butterfly, they were the larvae of the Giant Swallowtail! These are the largest butterflies in North America. Their wingspans can be more than six inches across.
Giant Swallowtails are the largest, most impressive of all our butterflies. They are pretty common in the Eastern half of the continent and can be found south into Mexico and Central America. They frequently visit butterfly gardens to nectar at lantana, bougainvillea, azalea, and Japanese honeysuckle. In the wild they sip from goldenrod and swamp milkweed. It is always nice to see a Giant Swallowtail.
But who knew that they started out so ugly? Giant Swallowtail caterpillars are truly the “ugly ducklings” of the butterfly world.
A female Giant Swallowtail seeks out citrus plants on which to lay her eggs. The larvae like to feed on citrus, but various related plants like wafer-ash, rue, and lime prickly-ash are also good larval food plants. The female lays her eggs singly on the tops of tender young leaves of the chosen host plant. The eggs are large for butterfly eggs: about a millimeter-and-a-half in diameter. This is about the size of a dot from a dull pencil point. You can see these eggs with your bare eyes, especially since the eggs usually get a grainy-looking, orange coating before they hatch. Once the egg hatches, the miniscule larva eats its eggshell and then starts feeding on the leaves.
Still, unless you are hyper-vigilant you will probably not notice the tiny babies eating away on your citrus trees. While small, the caterpillars rest on the top of the leaves and look even more like bird droppings (since small bird droppings are likely to be on the tops of leaves.) Presumably, this camouflage is quite effective against predators. Understandably, birds would leave them alone.
But by the time the caterpillars reach the patchy, plump, ugly “two inch size”, they have molted five times. This is the stage when most nursery workers and citrus growers find them. They are often referred to as “orange dogs” or “orange puppies” by people in the citrus industry. They are, of course, pests. Citrus workers readily dispose of the “orange dogs” before they can eat any more of the orange trees. Likely, they never realize that “orange dogs” grow up to be the lovely black-and-yellow butterflies that flit through the groves.
Unless you have very small trees, or are growing citrus commercially, it is unlikely that the “orange dogs” will do much damage. They eat a relatively small amount of foliage, compared to some butterfly species, and a large tree will regrow its leaves pretty quickly. You can consider a few orange leaves as the price you have to pay in order to have our country’s largest butterfly in your yard.
It is hard to believe that such an ugly caterpillar will turn into such a beautiful butterfly as this Giant Swallowtail. This butterfly is also the largest butterfly in the United States. It can be found in sunny gardens nectaring on lantana and bougainvillea. Jimmy Jackson Photo.
Or you can get out the Bt spray. Bt, is short for Bacillus thuringensis, a kind of bacteria that kills caterpillars that ingest it. It works by paralyzing the digestive tract of the feeding caterpillar. So some minor leaf damage will have already occurred by the time the Bt kills the caterpillar. But Bt is organic and safe to use around humans, pets and beneficial insects (like bees).
I wanted my tangerine tree seedlings to survive so I got out the Bt. The two “orange dogs” I had found on the seedlings were big and no longer feeding. I separated these two plants from the ones I sprayed with Bt. I want these “orange dogs” to become Giant Swallowtails. I want to see them make a cremaster (a supportive sling of silk) around their middles and hang on the twig as pupae. The pupae normally emerge as butterflies after 10 to 12 days. I want to see this happen. After all, they have already eaten the tangerine leaves; I might as well see what those leaves will become!
However, it is late in the year. The Giant Swallowtails often have three broods a year. The last brood hatches in September and once the caterpillars feed and pupate, they go into diapause. In diapause, they are in “suspended development” and won’t emerge from their chrysalises until spring. I may be waiting and watching these “ugly ducklings” for months!
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