Out of Their Tents, Onto Our Porches

A couple of weeks ago, dozens of caterpillars began showing up at my home in Fort Washington. They shimmied to the doors, crawled up the walls and camped out on the welcome mats. My daughter wanted to know when they would turn into butterflies, imagining a sky filled with exotic species like those on display at Smithsonian's Butterfly Conservatory.

Up to 400 butterflies flutter around a 1,200-square-foot pavilion inside the Museum of Natural History on the Mall: tiger swallowtails in yellow, pink, green and red, little tails on two of their hind wings; monarchs and morphos in bright yellow and iridescent blue; owl butterflies with spots on their wings that look like owl eyes.

During a recent interview, Nathan Erwin, who manages the year-round exhibit, called the place "spectacular." That was an understatement, given that the butterflies were beautiful enough to almost make me welcome the current caterpillar plague.

Only one problem: The bugs on my turf are eastern tent caterpillars, and they do not morph into butterflies. "It's a drizzly brown moth," said Michael J. Raupp, an entomologist at the University of Maryland. "Sorry, man."

Eastern tent caterpillars weave silk-like cocoons in trees. You've seen them. From a distance, they look like plastic grocery bags stuck on a limb.

The conservatory offers much better viewing. You can peer into an emergence chamber and, if the time is right, watch butterflies come out of their chrysalides. But be prepared to pay. The cost for adults is $6; for children 2 to 12, $5; seniors 60 and older pay $5.50. Tuesdays are free.

Or, you can just wait until mid-June and watch the newly emerged eastern tent moths flying around your porch light trying to mate. "It's quite romantic," Raupp said adoringly. (To learn more about the life and times of these and other critters, go to Raupp's Web site, http://www.bugoftheweek.com).

Frenzied as tent moths might be around the porch light, that activity alone does not explain their proliferation. "I'd be lying if I said I knew; only Mother Nature does," Raupp said. "Maybe it's because we didn't have a late frost at a critical time, when they were teeny-tiny, or maybe there are fewer predator birds; we just don't know. What we do know is that the caterpillar population is getting bigger and bigger. People are going crazy because the caterpillars are now in a migratory phase, looking for safe places to spin their little cocoons."

To make matters worse, after the tent moths mate and die off in June, the dreaded gypsy moth makes its debut. And this year's outbreak is expected to be one of the worst in a decade.

"The tent moth is primarily a nuisance, although these guys have been implicated in a serious disease affecting horses in Kentucky," Raupp said. "The gypsy moth, on the other hand, is an invasive species that gorges on tree leaves, especially oak. By the end of the summer, you'll be seeing a lot of defoliated trees."

So far this year, forest pest managers have sprayed nearly 100,000 acres in Maryland to slow the eastward spread of gypsy moth caterpillars. More than 23,000 acres in Frederick County and parts of northern Montgomery and Howard counties have been targeted. Similar prevention efforts are underway across the Washington area.

There are a number of ways that residents can protect their trees. One suggestion from the Maryland Home and Garden Information Center is to trap the caterpillars, using sticky or burlap bands on tree trunks. (For more ideas, go to http://www.hgic.umd.edu).

You can tell the difference between the two kinds of caterpillars by their colors. The tent moth caterpillar has a white strip down the back and blue- and gold-tinted fuzz; the gypsy moth caterpillar has red and blue spots.

I'd just as soon stomp them all, but that's a lot of gunk to scrape off my shoes. Growing up, I sometimes sprayed insect nests with gasoline and lit them. But gas was only 25 cents a gallon back then. Maybe I'll just leave the welcome mat out.

E-mail:milloyc@washpost.com