Euchaetes egle, the milkweed tussock caterpillar or milkweed tiger moth, is a moth in the family Arctiidae. It is a common mid to 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 (Weller et al., 1999). These are retained into the adult stage and deter bats, and presumably other predators, from feeding on them (Hristov and Conner 2005). Only very high cardiac glycoside concentrations deterred bats, however (Hristov and Conner 2005). Unpalatability is advertised with clicks from the tymbal organs (Simmons and Conner 1996).
From southern Canada, and south to Texas and Florida in North America (Wagner 2005).
One generation per year in the north, two or more in the south (Wagner 2005).
Eggs are laid in masses on the undersides of leaves.
Early instars appear slightly 'hairy' and gray. They skeletonize whole leaves gregariously, leaving a lacy remnant. They are gregarious until the third instar. Later instars sport tufts of black, white and orange (sometimes yellow) setae. The head capsule is black. The later instars wander much more, and may appear alone or in small clusters. Mature caterpillars are found from June onwards (Wagner 2005). Grows to a length of 35 mm.
The gray cocoon is 'felted,' presumably with 'hairs' from the larvae, and overwinters (Wagner, 2005).
Wings are yellowish-white. The forewings have bands of beige edged in faint black across them. The body is 'hairy' and yellow, with a row of black dots down the middle of the back. Males use their tymbal organs in courtship, calling to the females, and in defense against bats (Simmons and Conner, 1996).
Milkweeds (Asclepias spp.
) are the most common hosts, but it is also found on dogbane (Apocynum spp.
). They often prefer older plants of milkweed, and seldom share plants with monarchs Danaus plexippus
, which prefer younger plants (Wagner, 2005).
These plants produce a sticky latex that can impede feeding. Early instars avoid the veins by skeletonizing the leaves. Older larvae sever the veins of the leaves that supply the latex, to reduce the flow to the area they feed on (Dussourd and Denno, 1991).
- Dussourd DE, and RF Denno (1991). Deactivation of plant defense: Correspondence between insect behavior and secretory canal architecture. Ecology 72(4):1383-1396.
- Hristov, NL, and WE Conner, 2005. Effectiveness of tiger moth (Lepidoptera, Arctiidae) chemical defenses against an insectivorous bat (Eptesicus fuscus). Chemoecology 15(2):105-113.
- Simmons RB, and WE Conner, (1996). Acoustic cues in defense and courtship of Euchaetes egle Drury and E. bolteri Stretch (Lep., Arctiidae). Journal of Insect Behavior 9: 909–919.
- Wagner, DL, (2005) Caterpillars of Eastern North America. Princeton University Press.
- Weller SJ, NL Jacobsen, and WE Conner, (1999) The evolution of chemical defenses and mating systems in tiger moths (Lepidoptera: Arctiidae). Biol J Linn Soc 68:557–578
- Range map