Tuesday, April 27, 2010

Tent Caterpillars = Bird Food

Tent Caterpillars.  They seem to be everywhere these days, and that's got people talking.   I was talking with a friend about bluebirds yesterday, and she asked me - what can you do about those tent caterpillars?

I wasn't sure what she meant, so I asked.

The answer:  they're killing my trees.

It may look like they're killing your trees, but, really, they're not.

They eat leaves and it can look bad for the tree, but the leaves will, and do, grow back.  Watch and you'll see.  And if you leave them alone, the birds will eat them.  Tent caterpillars are bird food.  Why would you want to kill then when birds do it for free?

Are you sure?

Yes.  I Googled "tent caterpillars" back in March when I first noticed this egg mass on a cherry tree along the Chippewa River State Trail.

tent caterpillar egg mass

I discovered that these social caterpillars, while they may be "annoying" and "unsightly," are an important  food source for more than 60 species of birds, mammals (bears, mice and skunks) and frogs.

The bird predator list includes bluebirds, mockingbirds, orioles, chickadees, Blue Jays, warblers, Rose-breasted Grosbeaks, flycatchers and waxwings.

While cherry trees are the preferred hosts, tent caterpillars will feed on apples, peach, plum, birch, ash, willows, oaks and poplars.  The defoliated trees will grow new leaves in a just a few weeks.

Tent caterpillars overwinter as eggs and hatch out when the wild cherry buds start to swell open (this year in Wisconsin, it was early March).  I didn't witness the hatching, but entomologists say it takes a day or two.  Then the insects head to a crotch in the tree and spin their silken web - their first "tent." 
As they get bigger, they move to a larger fork in the tree and spin another, larger tent.  You can spot them in the tent when it rains, and during the heat of the day.  They leave the tent to feed on leaves at dawn, dusk and into the night.

It takes about 6 weeks before the caterpillars pupate.  Look for the white cocoons on the tree and in the vicinity of the tree.  The moths emerge in about 14 days.  They mate at night and the female lays her eggs in a day or two.  The male may live a week or so, but the females die after laying eggs.

Tent caterpillars are a spring phenomenon.  What you see in the late summer and early fall are "Fall Webworms," Hyphantria cuneaLike Tent Caterpillars, these animals appear during migration, providing food for birds.  They do not "kill" trees, they're more of an aesthetic "issue."

There's really no need to add poisons to your yard.  Lure birds to your yard with a water feature - and they'll do the job for you!


  1. I think I might have tent caterpillars on a peach sapling. I didn't see any egg mass. There were little bluish-black eggs dotting the leaves and some in the web that may one day turn into a tent. When they first come out are the very, very white and fuzzy so that you can hardly see the striping?

  2. P.S., we also found another use for them: nature study. My daughter keeps a nature notebook on things in our backyard.

  3. "Tent Caterpillars" are active in the Spring.

    If you have caterpillars "tenting" in the fall, take a look at "fall webworms."