When I left for work the other morning I noticed this big imperial moth (Lepidoptera: Saturniidae: Eacles imperialis) outside my door. It’s not unusual to see large saturniids on houses in the morning twilight. They’re often attracted to porch lights at night and then they stick around for a while. I’ve seen luna moths and other silk moths hanging out like this a number of times.
Imperial moth larvae feed on a wide variety of trees including oak, hickory, walnut, sycamore, basswood, maple, pine, and many others (Goldstein 2003). As with other saturniids, adults are incapable of feeding and only live for a few days while they focus on mating and laying eggs.
Found throughout much of North and South America, imperial moths are one of most widely distributed saturniids. In recent decades, however, these moths and many others like them have experienced a huge decline in the northeastern United States (Goldstein 2003). Imperial moths and several related species are even on a number of state endangered species lists in New England (Boettner, Elkinton, and Boettner 2000).
A number of possible causes for the decline were proposed, including habitat loss, mercury vapor lights, and DDT. Now there’s evidence that these saturniid moths are being heavily preyed upon by a parasitoid fly (Diptera: Tachinidae: Compsilura concinnata) (Boettner et al. 2000). This fly was introduced to North America from Europe starting around 1906 as a biological control agent for several pest insects, especially gypsy moths (Lepidoptera: Erebidae: Lymantria dispar) (Boettner et al. 2000). Gypsy moths themselves were accidentally introduced in Boston in 1869.
Unfortunately it was discovered the biocontrol flies were polyphagous, feeding on a wide variety of moth hosts with little specificity for gypsy moths (Boettner et al. 2000). Now many native saturniids are being decimated where the flies have spread. This serves as a good lesson on the importance of thorough study before biocontrol insects are introduced. The control agents can themselves become as much of a problem as the pests they’re introduced to control.
Boettner, G.H., J.S. Elkinton, and C.J. Boettner. 2000. Effects of a Biological Control Introduction on Three Nontarget Native Species of Saturniid Moths. Conservation Biology 14(6):1798-1806.
Goldstein, P.Z. 2003. Life history of the Imperial Moth Eacles imperialis (Drury) (Saturniidae: Ceratocampinae) in New England, U.S.A.: distribution, decline, and nutritional ecology of a relictual islandic population. Journal of Research on the Lepidoptera 42:34-49.