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phylum:      Arthropoda
class:       Insecta
order:       Lepidoptera
superfamily: Bombycoidea
family:      Lasiocampidae

Larvae of moths of Family Lasiocampidae, particularly Genus Malacosoma, these nasty, creepy little creatures are serious agricultural and forest pests, building huge silk tents in the forks of fruit trees and deciduous hardwoods and softwoods. Tons of them live inside these unsightly tents, sheltering at night and during the rain. During the day they swarm all over the outside of the tent, sunning themselves, crawling all over the tree, eating the leaves. Then they drop onto your head and down your neck when you walk under the tree. They are ugly, creepy, crawly hairy things with bright blue and yellow spots. They get everywhere and squish greenish-yellow under your feet. I hate them. They give me the goddam creeps.

Tent caterpillar infestations occur in waves every few years in forested areas of western and eastern North America, occurring in large enough numbers to defoliate whole trees and damage fruit. The best known species of tent-making caterpillar is the eastern tent caterpillar, Malacosoma americanum. Interestingly, not all Malacosoma build tents. M. disstria, notably, though a very destructive pest, migrating by the millions to new plants, does not build tents.

After mating in the fall, the adult moth, deposits several hundred eggs, covered by a thick, foamy brown crust, in bands around the twigs of the host tree. In early spring the eggs hatch and larvae from several egg masses congregate near a fork in a limb, forming the tent as they crawl around, leaving the tent silk behind.

About the only way to get rid of tent caterpillars is to soak the tents in kerosene or burn them (for real fun, do both). I remember my father and grandfather walking through the orchard with long flaming torches, setting the tents alight. When I was older, I myself would take the lopper and cut the offending branches, wrap them in newspaper and take them to the burn pile where I would set them on fire, watching them burn with vengeful satisfaction, knowing that I could never truly rest easy. They would be back next year.

Source for facts: Encyclopedia.com
Source for irrational hysteria: my childhood
On the West coast and especially in Western Washington, there are a few varieties of tent caterpillars, the most common being the Western Tent Caterpillar (Malacosoma Californicum) and the less common Forest Tent Caterpillar (Malacosoma Disstria). They primarily feed on Cherry, Alder, Apple, Willow, Birch, Cottonwood, Ash and Rose. Infestation can be rather disgusting with the unsightly tents in the crooks of branches, the ugly brownish-orange wriggling mass that can be seen basking in the sunlight, the gut wrenching (yet oddly satisfying) *pop* as you squish them under your shoes and the massive defoliation that occurs in their presence. There have been extreme seasons in the past, namely in the early 1960s and in 1986 where they have become an environmental hazard, causing the streets to become slick with the millions of migrating caterpillar carcasses. All that aside, there are several benefits to them.

One, the defoliation can allow more sunlight to reach the lower plant life that normally doesn't get as much sun during the spring and summer months. Generally the destruction caused by tent caterpillars isn't severe enough to kill any trees since they will just refoliate later, except if the trees are already weakened by other conditions like weather and prior diseases.

Two, the tent caterpillar is a valuable part of the natural food chain. Their poo is an excellent fertilizer for other plant life and caterpillars have many natural predators. Rodents and raccoons tend to like the caterpillar larvae while the birds looove the moths, since they all see a free meal. It is quite amusing to see the birds pick off the moths mid-flight. Predatory insects like ants, ground beetles and yellow jackets will eat them as well, or in other cases they will use them for their own ends. The Tachinid Fly for example, will attack and lay their eggs on their heads or other parts of the caterpillar bodies to serve as hosts for the parasitic larvae that will burrow into their bodies and kill them.

Controlling them is not really necessary unless you are seeking to have beautiful landscaping or are a farmer and they are destroying your crops. There are several methods that be used to control them, short of polluting with kerosene or possibly starting a wildfire (see above writeup). The best time to control the tent caterpillar population is during the winter season, where you can scrape or prune off the brownish egg casings that resemble styrofoam the adult moths have laid the previous summer on the branches and twigs of the host trees. Early in the season, you can just scrape off the tents as they form with your hands (wear gloves if you feel inclined) or prune infested branches and then stomp on them or burn the prunings (do NOT try burning them directly off the trees in your yard, you COULD burn your own house down if you are careless!). A biological agent, like Bt (Bacillus thuringiensis), is the most effective control for the ones out of reach and when properly applied to the foliage immediately surrounding the tents (figure a 2' radius) will selectively kill only caterpillars, since it is a bacteria that produces a neurotoxin that paralyzes their digestive tracts. Bt is only effective if the caterpillars eat the treated leaves and is quite safe to use as it will not harm plants, other insects, animals or humans. You can also resort to chemical sprays, but be warned, they could do MUCH more damage than the caterpillar, including killing all the helpful insects and their predators that you do want in your garden! Another thing you can do is to help out the natural predators by allowing them easier access in the morning and evening hours when the birds feed. You can simply punch holes in the otherwise impervious tents with a stick, or my favorite, shoot the tents with a paintball gun.

Yes, they are icky. Yes, they are disgusting. Yes, they do some damage. But let nature take its course and you will have a lot more plant and animal diversity seeing its way to your yard as the season goes on.

This info was compiled from just about every page I could Google™ on the subject. Just do a search for tent caterpillar if you want to see the whole bibliography or learn more than you probably ever wanted to know about entymology.

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