Sunday, June 24, 2012

A Tangled Web........

Look, up in that it a Spider? Is it a Fungus? No, It's a Tent Caterpillar!
Or is it?????
This time of year you may see web like tents in numerous trees. Most everybody has heard of the Tent Caterpillar (Malacosoma americanum). It has been reported to have been in the United States since the 1600's.
It looks like this:

This time of the year though, the Tent Caterpillar shares the tree tops with another web spinning caterpillar, the poorly named Fall Webworm (Hyphantria cunea). I say poorly named because it arrives in early Summer.
It looks like this:

Photo courtesy of University of Georgia.

The Fall Webworm is a native of North America, and feeds on many species of deciduous forest, shade, and fruit trees. It is one of the few American insect pests that has been introduced into Europe and Asia. Oops, sorry.
So how do you tell the difference? Look to see where the web or tent is.
If the webbing is in the crotches or forks of tree trunks and limbs, then it is the Eastern Tent Caterpillar.

Whereas the Fall Webworm prefers to just use the ends of branches.

Both of these insects can do a lot of damage to your tree by eating the leaves. An interesting tidbit of info though, and this is useful to remember when it comes time for controlling them, the Fall Webworm eats inside the protection of the web, they just keep expanding it. Eastern tent caterpillars typically feed during the day time and return to the nest at evening. They may remain in the nest during bad weather and eat later. The menu for both of these critters is a who's who of trees including, but not limited to...Birch, Crabapple, Ash, Blackgum, Willow and Ornamental Cherry trees, just to name a few.
The Eastern Tent Caterpillar lays a mass of eggs that encircles the twigs of the host plant. The dark brown, oval mass contains between 150 - 350 eggs, and has a varnished appearance. This egg mass overwinters on those twigs.
One of the ways to control the Eastern Tent is by removing the egg mass before it hatches, just cut off the branch and destroy it. Once the leaves fall off it is much easier to see them, look for something resembling this:

In the Spring the larvae hatch. When they are fully grown, they leave the host tree and find a place to spin cocoons. They pupate inside the cocoons for about three weeks before transforming into reddish-brown moths.

The Fall Webworm has a slightly different life history. The pupae over Winter as cocoons in the ground. They may also be found under loose bark and in leaf litter or mulch.
The Adult moth is also very different than the Tent Caterpillar.

Once the adults emerge they lay several hundred eggs that are deposited on the underside of leaves.

Here again controlling them can be as simple as cutting off the branch or leaf if you find an egg mass and destroy it.
Both of these insects have natural enemies, among them are birds, predatory stink bugs and toads. Some beneficial wasps will parasitize the eggs, larvae, and pupae.
If Mother Natures helpers are not doing a good enough job for you there is always Bacillus thuringiensis also known as Bt. It is a natural, organic product and works well to kill caterpillars if applied while the caterpillars are in the early stages of development and therefore small. Sprays are best applied in the early morning or late afternoon. Direct the sprays onto the foliage around the nests, as these leaves will likely be their next meal. Bt is the safest product to use and only kills caterpillars. It will not affect birds or beneficial insects that may be in the trees or feed on the caterpillars.
I know there are some people out there that really don't CARE which caterpillar is feasting on their prized ornamental Cherry tree, they just want them gone. I go back to an old military slogan, "To defeat your enemy, you need to KNOW your enemy". Having a name and where their eggs are and what the moths look like sounds like a good way to KNOW your enemy!
Happy Growing!


  1. You got a really useful blog I have been here reading for about an hour. I am a newbie and your success is very much an inspiration for me.

    Landscape Gardening Norfolk & Landscape Gardening Norwich

    1. Thank You Kevin! I know you posted this sometime ago, I am trying to get caught up.

  2. My webbing doesn't look exactly like either of these and it is everywhere on the trees from top to bottom. Some really large branches have fallen off that had it on them.