Isabella tiger moth

8129

Widespread and common

One brood. Early June to late July.

Deciduous woodlands, prairies

In its larval (caterpillar) stage, this tiger moth may be the most widely recognized moth in North America. The adult is less conspicuous but equally distinctive.

The caterpillar is up to 2″ long and is densely covered with stiff bristles (setae) from front to back. There are also a few longer, softer hairs extending from the front and back of the body. The setae are in clusters of several and are mostly uniform in length. On most caterpillars the setae are black on the head, thorax, and first few and last few abdominal segments; and orange on the middle abdominal segments. As the caterpillar ages and grows, it sheds its skin and setae (molts) several times. At each successive stage between molts (instar) it becomes more orange. On some individuals all of the setae are blond, brown, rust, or tan. There is a small breathing hole (spiracle) on both sides of each thoracic segment and all but the last abdominal segment. On pale individuals the spiracles are tan or white.

The adult moth has a wingspan of 1¼″ to 2″ and a total length of 15 ⁄16″ to 15 ⁄16″. The thorax is densely covered with long brown or yellowish-brown hairs. The abdomen is orange with an upper (dorsal) row of black spots.

The forewings are pointed and are uniformly light to medium orangish-brown. On some individuals there is a fringe of reddish-orange hairs on the outer margin. The veins are marked with faint brown spots. There is a series of black spots on the subterminal line and often one or more spots on the antemedial, median, and postmedial lines. The discal spot has a group of 3 to 5 black spots. The hindwing of males are pale orange with a black discal spot and black spots near the margin. The hindwing of females is pale rose but otherwise similar.

Deciduous trees and a wide range of low growing herbaceous and woody plants.

Adults do not feed.

Eggs hatch after about two weeks. Caterpillars overwinter under leaf litter or other debris, where they freeze solid. In the spring they become active and resume feeding. After a few days then spin a cocoon to pupate. Adults emerge in about a month.

Caterpillars are especially mobile in the fall. When disturbed, they curl up into a ball.

Adults are nocturnal. They are attracted to lights.

Sources: 7, 21, 24, 29, 71, 75.

Winter Forecast
Folklore says that the size of the orange band predicts the severity of the coming winter, with wider bands forecasting a milder winter. This means of forecasting is probably as accurate as the Farmer’s Almanac, though perhaps not as accurate as the National Weather Service.

Location: Pennington Co. MN

… this fall we had tons of Woolly Bear caterpillars crawling about the yard.

Location: Pennington Co. MN

Woolly Worm, the caterpillar stage of the Isabelle Tiger moth.