As a kid, I used to find caterpillars and raise them to adulthood. Nowadays, I don’t even see many caterpillars. Gone are the days, or so it seems, when every tomato plant had to be monitored for sphinx moth larva (“tomato worms”), dill was decimated by Black Swallowtail caterpillars, and each milkweed had its Monarchs-in-the-making. I especially miss seeing those impressive forest-munching machines, the silkmoth caterpillars (Saturniidae). Thirty years ago, most summers I could find Cercropia (Hyalophora cercropia) or Polyphemus (Anthera polyphemus) larvae, so big they were sort of gross and almost scary. Placed in an aquarium and kept supplied with a copious amount of fresh leaves, they’d balloon to three or four inches, and soon enough they’d spin a cocoon. The next spring I’d see the gratifying final result: a spectacular large moth (although some people find that, close up, their fat hairy bodies are still a little freaky). Here is a Polyphemus that I had the pleasure of welcoming into the world last week, courtesy of a friend who had raised some larvae he found in a more rural area.
Declines in silkmoths in the eastern U.S. are in part due to habitat loss and widespread, long-term pesticide use. Unfortunately, they are also victims of an introduced organism. Tachinid flies (Tachinidae) are a large family of parasitoids which feed on the larvae of other insects. Many are parasites of lepidoptera larvae. A non-native tachinid fly, Compsilura concinnata, was first introduced into North America 100 years ago (and up until 1986!) to control various pests, primarily gypsy moths (Lymantria dispar), themselves a non-native pest brought into the U.S. some 50 years before. Some tachinids are very host specific, but Compsilura proved to have quite catholic tastes and has been devastating to silkmoth larvae. Whereas parasitism of gypsy moths by Compsilura is generally around 5%, the mortality of silkmoth larvae in experiments at various densities was 52 to 100%. This research was done by University of Massachusetts-Amherst entomologist Jeff Boettner. Compsilura is also known to parasitize many other species – including swallowtail butterflies and other species that I see fewer of in my wanderings.
I don’t intentionally set out to find some subject that allows me to harp about introduced species in this blog. Working in an urban environment, if an interesting organism is not introduced itself, it’s a native organism that is impacted by a non-native one. It is often said that urban ecosystems are simplified ones, and that is true to a great extent — they tend to have less biodiversity and are often dominated by generalist species. But it seems that each time I delve into the life history of some bird, insect, or other creature that crosses my path, I am reminded of the complexity of all ecosystems, and the tangled web we weave when we tinker with the components.
UPDATE: Last night (9 June) while standing at dusk at a marsh awaiting a calling Common Moorhen, a Cercropia moth flew out of the woods and across the marsh. It was the first one I’ve seen in over 25 years!!
UPATE #2: Check out my first Promethea moth.
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 14:1798-1806.
Jeff and I went through the same undergrad program at the same university. Not only is he a great guy, but he is one of the rare scientists to gain respect and funding and publish in major journals even though he does not have a graduate degree. This makes him somewhat of a hero in my book.