Caterpillars Have Taken to Walking Now

Have you seen those spider web-like "baskets"  in tree limbs throughout the St. Louis area? Take a close look at the mostly impenetrable web structure and you'll see Eastern Tent Caterpillars, whose diet consists of leaves on the tree they have built their tents on.

In recent days, many of the tent caterpillars have left their cozy abodes and are walking around on driveways and backyard decks and patios, looking for a place to build a cocoon.

According to the University of Missouri Extension Service website, the Eastern Tent Caterpillar is a native defoliator that occurs as far west as the Rocky Mountains. The Extension Service website also indicates the preferred tree hosts for the caterpillar are wild cherry, apple and crabapple, but it will occasionally feed on forest and ornamental trees such as ash, birch, maple, oak, poplar, cherry and plum.

A cause for concern?

The good news, according to Chris Hartley, coordinator of education at the Sophia M. Sachs Butterfly House, is that once the caterpillars have left their tents, they are mostly harmless. And, while the web-like tents may be unsightly, they typically aren't damaging to the tree.

"They are worse on young trees," Hartley said.

On mature trees, not so much, Hartley said.

"Once they are off their host tree they won't cause any damage," Hartley said.

That includes any potential damage to landscaping foliage and backyard potted plants. Hartley said the caterpillars now are looking for a place to cocoon.

"They may make a cocoon in a potted plant, but they shouldn't cause any damage," he said.

As for getting rid of the caterpillars while they still are in their tents, Hartley said the only solution is to lop off the branch where the tent is located. Sprays or other bug killers typically don't work, he said, because they won't penetrate the webbing of the tent. 

Eureka-Wildwood Patch editor Julie Brown-Patton also and asked Nathan Brandt, a horticulture specialist with the University of Missouri Extension-St. Louis, about the creatures. 

If a particularly prized plant is being stripped of its leaves, Brandt said to scrape the tent and caterpillars into a bucket of soapy water or spray the plant with a product containing Bt., Thuricide, for example. "Otherwise just enjoy watching them and let nature take its course! Most plants can recover from ETC feeding without too much difficulty," he stated.

Hartley said he doesn't have the scientific data to support an opinion as to whether the mild winter has led to an increase in the Eastern Tent Caterpillar, indicating they typically are "a late spring kind of thing."  He said he has received reports from all over the St. Louis area about the caterpillars.

After emerging from their tents, the caterpillars will build a cocoon around itself on the sides of trees, among the debris on the ground, on brush and weeds, fences and even on sides of buildings, according to the Extension Service. Then in the fall, Hartley says, "little moths will emerge."