Bug Week


Tent Caterpillar

The BugWeek Web Team doesn’t think much of this next ORANGE AND BLUE! bug, the Eastern tent caterpillar.

And yet, we can’t help but admire its construction prowess and team spirit.

Known scientifically as Malacosoma americanum, this caterpillar is the larval form of a moth that’s part of the order Lepidoptera (no surprise there) and the family Lasiocampidae.

It feeds mainly on the leaves of trees in the Rosaceae family, notably those in the Prunus genus, including fruit-bearing species such as peach, cherry, apple and pear, as well as ornamentals such as the hawthorn and cherry laurel. If nothing in the Rosaceae family is available, they’ll also consume oak, willow and maple.

As the name suggests, the hallmark of this species is the tent-like structure it constructs from white silk threads the caterpillars secrete everywhere they go. The tents appear in early spring and can be easily spotted in the branches of infested trees. They house anywhere from 100 to 300 caterpillars, all of them hatching from the eggs laid by a single adult female moth. Each day, the caterpillars rebuild and expand their home, until it reaches about the size of a gallon milk jug.

Social behavior in caterpillars is fairly unusual, and this species displays a number of behaviors that help the colony survive — they leave scent trails (much like ants) that help members of the colony find food. And when they sense the presence of a predator, they’ll thrash their heads about, apparently to warn each other or perhaps to ward off the threat.

Like most caterpillars, these pests are voracious eaters and can strip the leaves off a substantial portion of their host tree, a situation that becomes more noticeable if multiple tents are involved.

Fortunately, the missing leaves come back after the caterpillars reach their final growth stage, also called an instar, and spin silk cocoons to settle down for the metamorphosis into adult moths.

But there’s a more serious problem associated with Eastern tent caterpillars — grazing horses occasionally eat them by accident, and the caterpillars have a toxic effect that can cause pregnant mares to miscarry and lose their unborn foals. This phenomenon apparently caused by the long bristly hairs called setae, which cover the caterpillar’s body.

A full-grown caterpillar is roughly 2 inches long, with a white stripe down its back and a pretty, complex pattern that mixes black, white, blue and a golden orange hue.

The Eastern tent caterpillar is sometimes confused with a related species, the forest tent caterpillar, Malacosoma disstria, which has a series of white dots down its back, rather than a stripe. You can read more about the species in this Featured Creatures document prepared by the UF entomology department.

The BugWeek Web Team has a final caution — if you happen to have a tree infested with the Eastern tent caterpillar and want to physically remove the tent with the help of a pole saw or other long-handled tool, try not to stand directly underneath it as you work. Besides the caterpillars themselves, that silk tent contains thousands of caterpillar droppings and you really don’t want to be caught in the downpour when the bottom of the tent ruptures.

Trust us, we know.