Tent Caterpillar

Pull the tent out of the fork while the caterpillars are still inside, because that is when the whole colony is home. Twist the silk around a stick or a broom, dump it in a bucket of soapy water, and do not burn it on the tree, because fire injures the bark worse than the chewing.

People still say tent worm, then tent caterpillar. In spring, look at the V of a cherry, apple, or crabapple. Dense, cottony silk sits in that crotch. Hairy black caterpillars with a white stripe down the back leave that tent to eat the new leaves, then they come back when it rains or when the day heats up. A healthy tree usually puts out a second flush. A young cherry that is going bare cannot wait.

Pull the tent off the fork while they are inside

The colony sleeps in the silk. Early morning, evening, or a cool rainy day, they are packed in there, so that is when a twist finishes the nest. Wrap the tent around a stick, a broom, or a pole with a nail across the end, and the caterpillars come with it. Drop the mass in soapy water. Wear gloves, because the hairs can itch.

On a small cherry or a newly planted apple, prune that small fork if the cut will not wreck the shape. The silk is temporary, so a hard prune on a mature tree is the lasting injury. Do not reshape a canopy to chase a nest you could have twisted off.

A hole in the tent still helps, because birds and wasps cannot hunt through intact silk. A strong hose that tears it open does the same job. Do not torch the nest on the tree. Fire injures bark and buds worse than the caterpillars, and it is a fire hazard.

1. Confirm this moth. Spring. Dense silk in a fork. Hairy caterpillars with a white stripe, leaving the tent to feed.
2. Pull or prune a tent you can reach while they are inside. Twist it off. Dump it in soapy water. Do not burn it on the tree.
3. If this is a tent or two on a healthy mature tree, wait, or tear the silk open for birds and wasps. Water through dry weather.
4. Bt only while they are still small and you can wet the leaves they eat, if the tree is young, already stressed, or going bare.

A healthy tree puts out a second flush

They eat early, right as the buds open, so a mature cherry, apple, or crabapple usually leafs out again in a few weeks. One spring of tents is looks, not a take-down. The chewed leaves will not green up, so the tree looks ragged until that second flush covers it.

Act when the tree is young and most of the canopy is inside silk, or when the same small cherry is stripped year after year in drought. A couple of tents on a bearing apple is looks. A newly planted crabapple going bare is the year to pull, or to spray while they are still small. Black cherry in a fencerow wears this insect most years and still leafs out; do not take the wild cherries down as the plan, because that fencerow feeds a lot more than this moth.

Water through dry weeks. Do not take the tree down for one April of silk. When they finish feeding they wander off to spin cocoons on fences, siding, and litter, so the empty tent stays until you pull it. Rain does not take this silk the way it takes a late-summer web on the tips.

The tent sits in a fork in spring, and they leave it to feed

Confirm is location and season, not how hairy the worm looks. Dense silk in a branch crotch in spring. Hairy caterpillars, black, with a white stripe down the back, blue spots along the sides, and sparse long hairs. About two inches when grown. They leave the tent to feed, then they come home. Tap the tent in the heat of the day, and they are packed inside.

Eggs sit in a shiny, varnish-like band around a pencil-size twig. One mass holds about 150 to 400 eggs and feels like styrofoam. They hatch as wild cherry buds open, so a small tree can look as if it never leafed. One generation a year. The moth is reddish-brown with two pale stripes on the forewing. They spend most of the year as that egg mass.

In the West, western tent caterpillar also makes a crotch tent and leaves it to feed, so the same pull works. Forest tent caterpillar is a cousin with keyhole marks down the back. It spins a silk mat on the trunk, and it does not build a tent.

A dirty web on the tips in August is a different moth

Fall webworm wraps the outer tips in late summer and eats inside that silk. That is not a dense nest in a fork in April. See fall webworm. Do not run their tip-pull here.

Forest tent caterpillar has a row of white keyhole marks down the back and does not build a tent. It rests on a silk mat on the trunk or a limb. There is no nest to twist. Do not run a fork-pull on a tree that has no tent.

Bagworms are individual spindles of silk dressed in the plant's own foliage, often on arborvitae and juniper. See bagworm. Do not pick bags here.

Spongy moth — people still say gypsy moth — is hairy, with five pairs of blue bumps and then six pairs of red, and it does not spin a communal tent. See spongy moth. Do not run their burlap skirt here.

If the worms are smooth, rear into an S in a group, and you count six or more fleshy extra legs, that is a sawfly, related to wasps, so a Bt spray made for moth caterpillars will not kill them. See sawfly.

Bt on the leaves they eat, while they are still small

Bacillus thuringiensis (Bt, the kurstaki strain) has to be eaten, so spray the foliage they are chewing, not the water-repellent silk. Use it when the tents are first showing and the caterpillars are still young, about an inch or less, because large ones shrug it off and have already done most of the eating. They leave the tent to feed, so a fog on the outside of the nest does not reach them. Follow the label in your hand.

Skip the brand aisle if a stick would have finished the nest. A spray after they have wandered off to pupate will not rewind the leaves, and it will not pull the empty silk down. If the tree is in bloom, skip a product that kills bees, because those flowers are the day's work for pollinators, not this moth's nest.

Scrape the varnish egg mass off the twig in winter

After the leaves drop, walk the cherry, apple, and crabapple and look for a shiny dark band wrapping a pencil-size twig. It looks varnished and feels like styrofoam. That mass is next spring's tent. Scrape it with a thumbnail into soapy water, or prune that twig if the cut is one you would make anyway. One mass is one colony.

On a tree with many masses, a labeled dormant oil can smother eggs you cannot reach with a thumbnail, because the oil has to coat them. Motor oil is leftover. It injures the bark. Leave the empty brown tent if you already pulled the worms; rain will not take it, so twist it off when you scrape if it still bothers you.

Related reading

• Fall webworm — loose silk wrapping branch tips in late summer; larvae eat inside the web.
• Bagworm — individual spindle of silk plus the plant's own foliage, often on evergreens.
• Spongy moth — hairy, blue then red spots, no communal tent in a fork.
• Fall cankerworm — looping inchworm in spring; no communal nest in a crotch.
• Sawfly — six extra legs, often an S in a group; Bt made for moths will not kill them.