For the Birds Radio Program: Tent Caterpillars and Cuckoos

Original Air Date: June 26, 1989

Is it true that to eat a tent caterpillar you have to be cuckoo? (4:03)

Audio missing


(Katie: “Look, Mommy, tent caterpillars!”)

There is a time of wonder and curiosity in the lives of most people when army worms are exotic and interesting creatures. The forest tent caterpillar invading the Northland this year is actually rather handsome if you can look at it objectively—it has shiny deep blue stripes along its sides and a row of golden keyhole-shaped dots along the center of its back. Forest tent caterpillars don’t build the familiar white community tents that their close relative, the tent caterpillar, does—instead, it’s every worm for himself. My five-year-old daughter Katie thinks they’re simply wonderful—she’s made pets of eight or nine of them which she diligently feeds and cares for every day. There aren’t too many in my Lakeside neighborhood, but some areas are infested so badly that even a child’s sense of wonder could quickly be displaced with less positive emotions.

Tent caterpillars become so extraordinarily abundant during their invasion years because they have few natural enemies. Only one Northland species of bird, the Black-billed Cuckoo, eats them with gusto, and that species is declining, in part from eating pesticide-laden caterpillars. Cuckoo numbers are up this year in the Northland. They’re extremely secretive and aren’t often seen, but if you pay attention you may hear their soft “coo coo coo,” sometimes throughout the day and especially before a rain.

(Recording of a Black-billed Cuckoo)

During good tent caterpillar years it’s also possible to see or hear a Yellow-billed Cuckoo. This close relative of the Black-bill has a more southerly range, but occasionally comes up here for an army worm feast. It’s call has a weirder quality than the black-bill—it’s called the rain crow in the south.

(Recording of a Yellow-billed Cuckoo)

Cuckoos not only eat hairy caterpillars, they also feed them to their young in huge numbers, without even killing the wiggly larvae first. Although cuckoos are the only birds specialized for this kind of diet, which may explain their name, other birds do eat at least a few army worms. Orioles and starlings have been recorded eating them, but only after peeling off the hairy skin. Crows also pick at them on roadsides, but they too may concentrate on the insides. I’ve watched a robin carrying one around, but it didn’t seem to know what to do with it.

Because forest tent caterpillars are so voracious, a lot of people are naturally calling for widespread spraying. These people seem to believe that one good spray job and the larvae will vanish like magic, forgetting that toxic chemicals will remain behind to poison honeybees, ladybugs, and other necessary invertebrates indiscriminately. Most pesticides are also toxic to birds, fish, and even mammals. Those little lawn flags that warn adults of toxic sprays don’t protect birds or toddlers who can’t read. No, poison spread throughout the northland would be at least as objectionable as army worms, and its toxic effects would last a lot longer than the damage from the caterpillars. Trees attacked by army worms usually recover, and even if a tree can’t produce apples one season, the apples wouldn’t have formed if pesticides killed the pollinating bees anyway. There is great beauty in the natural world, but in order to keep it, we have to accept a few problems, too. Look at forest tent caterpillars with the eyes of children, and they’re a lot more fun.

(Recording: kids, singing “I Know an Old Lady”

That was the Joey, Katie, Tommy, Seth, and Katie, this is Laura Erickson, and this program has been “For the Birds.”

(Recording of a Black-billed Cuckoo)