Tent Caterpillars & Fall Webworms

Fall Webworms:

Webworms are moth caterpillars. They over winter as pupae in silken cocoons that you will find stuck under or in everything in your yard. The moth stage lays eggs under leaves in the trees they like to feed on. Webworms are supposed to come out in the fall, hence their name of Fall Webworms. They don’t always behave properly and can appear in the spring or whenever they want. They can have several generations in a growing season, but the fall incidence is usually the worst as the population is greatest and they are more noticeable than in the spring.

Fall webworms make webs around the leaves they are feeding on for protection, usually around the outside of the trees. You will see the skeletonized leaves in the webs. These webs can encompass a limb or even the whole tree in good times (for the worms). Even these heavy infestations rarely kill healthy trees as they usually store enough food to re-foliate several times to protect against problems like late freezes, droughts, and probably webworms too. In the fall, the trees will drop their leaves for winter anyway, so feeding them to worms isn’t too much of a problem for the trees.

The worms are about 1 inch long, yellow to greenish, with clumps of hairs all over them. They are fast too. They are not supposed to be able to sting, but some people have claimed to have been stung, usually when squeezing them. So don’t worry about them, but don’t play with them either.

Early control is best when the worms are small, but then they are less noticeable. Since the webs protect them, breaking up the webs is the best way to allow natural predators like wasps and birds to get to them. For spraying pesticides, you need a high pressure applicator to get Bacillus thuringiensis (Bt) or spinosad through the web in tops of trees and onto the leaves for the worms to eat. We have a Chapin (was Gilmour) professional brass body hose end sprayer that reportedly can do 35 feet if your water pressure is good, but for higher trees you will need someone with better equipment like Rohde’s to spray for you. Of course you can try to hit tennis balls or sling shot rocks into the webs to break them up, but you need to run out of the way when they come back down, and the worms probably can repair the web quickly being as fast as they are. Insecticidal soaps and horticultural oil can also kill webworms, but again, you need to apply them directly on the worms in the webs to be effective.

http://entnemdept.ifas.ufl.edu/creatures/trees/moths/fall_webworm.htm: Very good photos

Tent caterpillars:

Tent caterpillars are also moth caterpillars. There are four main species; Eastern Tent, Western Tent, Forest Tent, and Sonoran Tent Caterpillars. The worms have similar but distinct markings to identify each of them. Each species can have different preferred trees they like to feed on. Tent caterpillars except the Forest Tent caterpillars make a web in the crotch of trees branches they use for protection when they are not feeding. They wander out to feed. Forest tent caterpillars rest in mass on a silken mat on tree trunks or large branches where they are most noticeable.

All tent caterpillars overwinter as a hard mass of eggs around tree twigs. The eggs hatch as deciduous trees bud out in spring, mid-February to mid-March. They have only one generation in a growing season and end their time in May or June when they pupate in a silken cocoon. You will see the worms traveling around the ground looking for hiding places to pupate. They hatch out as moths in about 3 weeks to lay eggs again for the winter. The degree of damage varies from year to year, but even it heavy years, healthy trees will be able to recover without long term effects.

Treatment for tent caterpillars may not be necessary as their purpose in the big scheme of things is to feed baby birds during spring nesting season. Since they do not eat within a web like fall webworms, they are easy picking.
But if you have to do something:

·       Trichogramma Wasps early in spring may get some eggs, but not the adults.

·       Dormant plant oils in the late winter will get the eggs also.

·       Bacillus thuringiensis (Bt) is effective, but works better on young worms.

·       If you can tear up the web by spraying with a garden hose or using a stick, birds, lizards, wasp, and other insects can eat them.

·       Plant oil sprays can work, but require complete coverage which is hard in the top of a tree, but easy with Forest Tent caterpillars when they mass on a tree trunk.

·       Spinosad containing products will work also, but will harm bees if wet. Spray in the evening so it will be dry when bees come out in the day. Spray Bt or Spinosad on foliage around the webs as that will be what they eat first. You don’t need to spray the whole tree.

Ordinarily the tree will grow new leaves with little harm to itself when the caterpillars finish their life cycle. Just wait them out and release wasps or use dormant oil sprays next year.

http://extentopubs.tamu.edu/e-218.html: Covers all 4 caterpillars
http://texasinsects.tamu.edu/eastern-tent-caterpillar/ : Eastern and Forest Tent Caterpillars
http://citybugs.tamu.edu/2015/04/10/tent-caterpillars-without-the-tent/ : Forest Tent Caterpillars
http://www2.ca.uky.edu/entomology/entfacts/ef423.asp: Eastern Tent Caterpillars
https://en.wikipedia.org/wiki/Tent_caterpillar: Detailed information
https://en.wikipedia.org/wiki/Eastern_tent_caterpillar: Detailed information:
http://www.dec.ny.gov/animals/7111.html: Forest Tent egg pictures
https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5303047.pdf: Western Tent Caterpillars