Webs in Your Trees: Fall Webworms and Tent Caterpillars

Late summer in Volusia County, the calls start about "spiderwebs" taking over the pecan, the persimmon, the sweetgum or the oak. Big, messy, dirty-looking silk tents out on the ends of the branches, sometimes a dozen of them on one tree, with leaves inside turning brown.

That is fall webworm. It looks like something is killing the tree. It almost never is, and the way most people try to deal with it does more harm than the caterpillars.

Fall webworm vs. tent caterpillar

Two different insects, two different seasons, both easy to identify once you know where to look.

Fall webworm builds its web at the tips of branches, enclosing the leaves it is eating, and it does so from mid-summer into fall. The web expands outward as the colony eats. The caterpillars are pale, hairy, with black or red heads. Multiple generations a year in Florida, so webs can appear from June onward and pile up by September.

Eastern tent caterpillar builds its tent in the crotch of branches, near the trunk, in early spring, and the caterpillars leave the tent to feed. By late spring they are gone. Much less common on the coastal Volusia landscape than webworm, and more of an issue on wild cherry.

If it is late summer and the web is at the branch tip, it is webworm.

What they do to the tree

Webworms eat leaves. On a large tree they eat a small fraction of the canopy, and by late summer the tree has already done most of its year's photosynthesis. A healthy oak, pecan or sweetgum with a dozen webs loses effectively nothing.

The cases that matter are:

• A small or newly planted tree where the webs cover most of the canopy
• A tree that is already stressed and thin, where losing more leaves adds to the problem
• Repeated heavy defoliation on the same tree several years in a row

Even then, the damage is stress, not death.

What not to do

Do not burn the webs. Every year somebody in Central Florida sets a tree on fire, or themselves, with a torch on a pole. Fire kills the branch, scorches the bark, and often does not kill the caterpillars sheltered deeper in the web.

Do not cut off every webbed branch. Pruning out a few webs on a small tree is fine. Lopping off the ends of a dozen branches on a mature tree to remove webs is unnecessary wounding and ruins the shape. Our post on where the cut goes explains why random tip cuts are a bad idea.

Do not spray a mature tree from the ground with whatever is in the garage. Coverage is poor, the caterpillars inside the web are protected, and you kill the wasps and birds that eat webworms.

What actually works

On a small tree you can reach, the simplest fix is to open the web with a stick and let the birds and wasps in, or pull the web down and drop it in a bucket of soapy water. That handles most residential cases.

On a tree where the infestation is genuinely heavy and worth treating, the product that works is Bacillus thuringiensis (Bt), a bacterial insecticide that only affects caterpillars. It needs to reach the leaves the caterpillars are eating, which means opening the web first, and it works best on young larvae. Spinosad is another targeted option. Both are available to homeowners; on a large tree, a licensed applicator with the equipment to reach the canopy is the realistic route.

On a large healthy tree, the right answer is usually nothing. The webs are ugly for a few weeks and the tree sheds them with the leaves.

The bigger picture

If a tree is heavily hit by webworms year after year while the neighbors' trees are not, look at the tree rather than the insect. Stressed trees attract and sustain more pests. That usually means something at the root zone: a buried flare, compaction, a grade change, or chronic drought in sandy soil. See Watering Trees in Florida Sand and Girdling Roots for the usual suspects.

Frequently asked questions

Will the webs go away on their own?

Yes. The caterpillars finish feeding, drop to the ground to pupate, and the web weathers apart over the following weeks. By the time the tree drops its leaves, the webs are gone.

Are the caterpillars dangerous to touch?

Fall webworms are hairy but not stinging. Some people get mild skin irritation. Puss caterpillars and saddlebacks, which do sting, are a different insect and are not web builders.

Should I fertilize the tree to help it recover?

Not in response to webworms. A healthy tree does not need it, and nitrogen fertilizer pushes soft growth that attracts more pests. Water during dry spells and leave the tree alone.

Can you remove the webs for me?

Yes, on trees where it makes sense as part of a pruning visit. On a large tree, we will usually tell you to leave them, because the cure costs more than the problem.

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ArboristRX assesses tree health across Edgewater, New Smyrna Beach, Port Orange, Oak Hill and Volusia County. Call (386) 444-5959 if a tree looks like it is losing the battle.