Euchaetes egle, the milkweedtiger moth or milkweed tussock moth, is a moth in the family Erebidae and the tribe Arctiini, the tiger moths. The species was first described by Dru Drury in 1773. It is a common mid- through late-summer feeder on milkweeds and dogbane. Like most species in this family, it has chemical defenses it acquires from its host plants, in this case, cardiac glycosides. These are retained in adults and deter bats, and presumably other predators, from feeding on them. Only very high cardiac glycoside concentrations deterred bats, however. Adults indicate their unpalatability with clicks from their tymbal organs.
Range
It is found from southern Canada and south through Texas and Florida in North America.
Life cycle
There is one generation per year in the north and two or more in the south.
Egg
Females lay eggs in masses on the undersides of leaves.
Larva
Early instars appear slightly hairy and gray. They skeletonize whole leaves gregariously, leaving lacy leaf remnants. They are gregarious until their third instar. Later instars sport tufts of black, white and orange setae. The head capsule is black. The later instars wandermuch more, and may appear alone or in groups of 2 to 10. Mature caterpillars occur from June onwards. Larvae grow as long as 35 mm.
Pupa
The gray cocoon is felted, with hairs from the larvae, and overwinters.
Adults
Wings are grayish. Abdomens are hairy and yellow, each with a row of black dots on its dorsum. Males use their tymbal organs in callingfemales and in defense against bats.
Food plants
This moth frequently uses milkweeds and sometimes dogbane as larval host plants. Larvae often feed on older milkweed shoots, and seldom share shoots with monarchs, which prefer younger ones. Dogbanes and milkweeds produce a sticky latex that can impede larval feeding. Early instars avoid the veins by skeletonizing the leaves. Older larvae sever the veins that supply the latex, which reduces latex flow to the area they feed on.
