Perhaps especially if you live in the eastern half of the US, please learn to ID the gypsy moth catepillar and destroy them. They are horribly devastating to the hardwood forests. Check with your local forestry officials to see what, if any, eradication or control measures are recommended and follow their guidelines.

Just enjoyed watching an invading army of these critters, having dropped from a tall wild cherry tree, marching across our patio as though to carry away our house just west of Charlottesville, Virginia.

If you choose to remove the tents from your trees, be aware that the caterpillars are out crawling around during the day, feeding their gluttony. They return, as the evening cools, to the warmth of the commune. So the best result comes from timing their involuntary drop into soapy water for the hour or so just before darkness, when the nesting population is at home watching American Idol.

Although they do love eating our fruit tree leaves, I don't believe these were Gypsy Moths, in our case. The caterpillars don't look like the ones I saw online.

Caterpillars, at least the tent ones in our apple trees, do not walk down hill.    I used cardboard boxes made into cones wrapped around the apple tree trunks like hoop skirts above the grass.

After spaying high pressure water to knock em off the trees they climbed up the tree trunks and became stuck under the cones, totally unwilling to walk down and around the hems of the cones.

I've been told that it works well just to destroy the tents, whether or not anybody's home at the time... they need the tents to shelter in at night and can't build fast enough when they come home at dusk. Mess them up with a stick, even.

I agree that the best method is to physically remove the eggs before hatching or remove the tents.  However, a 'natural' alternative is to spray the tree with a product called Dipel--it is NOT a conventional chemical pesticide, but a bacteria (Bacillus thuringensis kurstaki) that when ingested proliferates and kills the caterpillars.

Higginator is right about bacillus thuringienis kurstaki (BT), which is also effective against gypsy moth caterpillars. However, keep in mind that BT kills ALL caterpillars, even the good ones, so, first of all, know your caterpillars. Second, read up on the product because it is most effective when used in the early stages (instars) of the caterpillars' lives.

To reiterate the point made by wildjersey, gypsy moths do not create tents and in fact, the caterpillars and adult moths look quite different.  The Eastern tent caterpillar has a white stripe down its back and small blue dots on the sides.  The adult moth is brownish with two white stripes on the wing.  The gypsy moth caterpillar is extremely hairy with red and blue dots and no stripe on its back.  The adult female moth is white with brown stripes and is quite conspicuous.
 It is not difficult to compare these two species and the treatment methods differ.  Please take the time to identify these insects before taking action.  As Umbra stated, the tent caterpillars are native and our trees are more resilient to their outbreaks than to those of gypsy moths.

Insects are sentient animals too.  We are up in the air, though, about the nature and quality of their sentience.  As a promoter of animal rights myself, I am yet at odds with many fellow-travelers, of the sort who would protest bitterly everything that is being discussed in this thread.

It is important to understand (something that many animal-rights promoters do not, to our general sorrow) that animal-rights ethics is most certainly NOT monolithic; it is NOT a complete doctrine; it is a work in progress.  As a branch of philosophy, fortified by natural science, it positively encourages questions, and differences of opinion.

And how to evaluate the sentience of arthropods is a big issue.  There are those who refuse to wear silk, or to eat honey -- and that is fine, a decision based on good observations into the lives of silk worms and honey bees.  But we do not know nearly enough so as to declare that people who wear silk or eat honey are ipso facto heartless and cruel.  Thoughtless maybe, but not heartless; and maybe even they do it with some thought and consideration.

As for those who dine on crustaceans: lobsters, crabs, shrimp, and crayfish: well, that is a bit more complicated.

In the case of caterpillars, they have a certain degree of sentience; how much is not clear.  Exterminating them, or at least making life very difficult for them, is perhaps justified, but we have to be the judge in each case.  Being frustrated beneath a cone, till we starve to death, is not a nice way to die; nor is being poisoned with toxins, so that our innards feel like fiery knives; nor is being left outside over night to freeze, because our home has been destroyed.

No one can force a change in anyone's mind, regarding how he and she relates to animals.  But at least we may ask everyone to pause and think about what kinds of beings animals truly are: not resources, not endlessly exploitable, not additions to or subtractions from the decor that we artificially create about us; but rather independent beings with their own lives and interests.

So, exterminate the caterpillars, if you feel you need to.  But we aware of what you are doing, death-wise.

Umbra's implicit solution works fine for me: Sit back and observe the cycles of nature.

I'm all for letting flora and fauna and bugs and such alone, no matter how icky if they serve a purpose in the earth's cycle(17 year cicadas come to mind, which the birds and squirrels think are delicious), but can someone please tell me what creature actually eats tent caterpillars?  I have a balcony in N. VA that backs to woods, where the wild cherry trees (T.C.'s favorite roost) have been increasingly colonized by tent caterpillars over the past 6 years.  I also have a number of wild birds, squirrels, fox, and have even seen a deer in the narrow woods corridor between condo developments.  However, I have yet to see any bird or other critter feasting on the plethora of tent caterpillars.  Not even the starlings...As far as I can tell, they're just weakening the wild cherries.  Anyone have a thought as to their larger purpose?

We blind fallen mortals are ill-equipped to discern the ways of the Creator as they extend inscrutably before us.

Wherefore the Creator in the Creator's goodness has sent us Prophets, such as Umbra Fisk:

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Although a boom year for caterpillars can denude trees, the trees will usually recover, sending out a second set of leaves and only suffering a bit of a setback in their growth. The denudation can actually benefit smaller trees lower in the canopy, which may receive more sunlight than usual and experience a good year of growth. The bountiful caterpillars will provide a plethora of food for their predators and poop for the forest floor.
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Who the predators might be is left unstated.  Parasitic wasps maybe?

Dear Umbra and caterpillar chatters:

My colleagues and I pondered these furry colleagues on a post-lunch walk through the Virginia woodlands near our office today.

The tents were vacant and the wild black cherry tree that once supported them in their congenial hairiness nearly denuded. We could palpably hear the tree sighing in relief and preparing to releaf.

A couple of points of clarification about the life of these larvae. That trail they leave upon heading out for work in the morning is not slime. It is silk. As in pajamas. Few people sport slime pajamas but this natural fiber they create is pretty cool. No, I haven't harvested it and spun my own jammies however.

The eastern tent caterpillar is a very picky eater-- as are many if not most caterpillars. It's favorite food source is wild black cherry, one of our noblest hardwoods. These life forms  have co-evolved quite satisfactorily. Put some of these caterpillars in a non-native tree or shrub-- say an exotic cherry, plum, apple or crabapple perhaps-- and the damage done might be significant or at least more noticed. But generally, just throw the critters some native cherries, plums or crabapple, and no one really gets hurt.

As for who eats what, I've observed a number of our migrant and nesting warblers chow down on young tent caterpillars if the sequence of caterpillar growth and warbler arrival is just right. And then there are those magnificent cuckoos which also love to pillage the invasive gypsy moth caterpillars. It is said that these wonder birds gobble down the caterpillars, hairiness and all, and once their stomach lining is maxxed out with spiny protuberances from caterpillar bodies, they are able to vomit (or cough if you will) up the old lining and start perforating the new one, all the time relishing the gourmet goo contained within. Is that a cuckoo call I hear or a cuckoo cough?

Bt, the "safe" biopesticide sold as Thuricide and under other names does impact other caterpillars in those wild black cherry trees. In addition to the eastern tent caterpillars that some find offensive, wild black cherry also supports the caterpillars of the generally more appreciated eastern tiger swallowtail butterfly and that of the red-spotted purple as well. And there are other beautiful leaf eaters on this tree as well, but I've rambled enough.

Wildscaper

Thanks, Wildscaper, that was good and sweet of you to share your ramble in the Virginia woods.

Your name for warblers, "wonder birds," is brilliant.  I have little or no luck observing them; they are stunning, and plainly make their presence felt; but they are also so small and swift and transient, that I can barely try to keep track of one for just a few seconds, until I end up feeling seasick.

By some blessing, a few weeks ago, while I was sitting under a tree on the campus of the school in NJ where I teach, I was for around ten minutes graced with the presence of two Worm-eating warblers, Helmitheros vermivora (as you know, there is a separate warbler genus Vermivora, with a few species, who presumably are also "worm-eaters," and might include the predators of the tent caterpillars), not too hard to identify thanks to their distinctive head-striping, but supposedly not too common.  They were entertaining one another, flitting back and forth between the tree's canopy over my head and the grassy lawn just a few meters in front of me.  Perhaps they were a courting couple.  That was the first time I had ever seen warblers sit in grass under the open sky.

This reminded me of a conversation I had a couple of years ago with a Native American artist, whom I met at the Mashantucket Pequot Museum in southeastern Connecticut (a terrific place, in a beautiful part of the country).  She had on display a number of works in different media, most of them incorporating imagery of different animals, including hummingbirds.  I commented to her that while we in the European tradition give prestige to big, powerful animals in our artistic symbolism, especially certain predators, and large hoofed animals with horns or antlers, Native Americans have been able to discover great power even in small, fleeting animals whom we Euro-Americans have tended to consider insignificant, such as lizards and insects and small birds; in fact, the great and terrible god of the Aztecs is named Huitzilopochtli, "Hummingbird on the left" (or "from the North," which is the same thing if you are oriented correctly toward the East).  She agreed, and added that when one of those small fleeting animals allows himself/herself to be seen by you for a bit longer than would happen during a quick crossing of paths, then in her people's tradition, that meeting is a moment of blessing and spiritual power, which deserves to be dwelt on, and appreciated.

As for the predator/prey relationship between warblers and tent caterpillars, we should pay careful attention to this one, and others like it, which may be being affected by global climate change.  If the migrations of birds such as warblers are set in motion by astronomical signals, while the life cycles of their prey items such as caterpillars depend on local temperatures, then it will happen that the birds will arrive in a region, where they expect to feed on their preferred prey items at a relatively younger stage of development, only to find them more developed and less accessible.

So another moral perhaps to be drawn from your ramble in the VA woods, Wildscaper, is that the tent caterpillars should be left alone, for the sake of the warblers.