Most Texas County residents have by now noticed that this is a big year for tent caterpillars.
And the Missouri Department of Conservation has indicated that there are, in fact, two types with bigger than normal populations in 2012: the Eastern tent caterpillar and the Forest tent caterpillar. According to MDC Forest Entomologist Rob Lawrence, mild conditions this past winter led to an increase in the bugs’ numbers.
“We’ve been getting lots of reports of tent caterpillars from eastern, southern and southwestern Missouri,” Lawrence said. “It makes sense that we would be seeing bigger populations of both of these insects. They both over-winter as egg masses on branches. Being that exposed makes them more vulnerable to severe winter temperatures, so conversely this mild winter should have benefited them, as long as they don’t hatch too early and get zapped by hard freezes.”
In most cases, tent caterpillars being seen in Texas County and the Ozarks are of the Eastern variety, which actually build the infamous tents. But Lawrence said he has also received a report from the St. Louis area of large numbers of Forest tent caterpillars, a closely related species that does not make a tent.
They are often found in more heavily wooded areas and feed on oaks, maples and many other tree species.
“If you are observing large numbers of either of these, I would appreciate a quick report of that,” Lawrence said. “But I would especially like to hear from you if the Forest tent variety is causing significant defoliation.”
To identify each variety, look for distinctive markings. The Eastern tent caterpillar has a white stripe down its back, while the Forest tent has what look like white footprints or keyholes on its back.
Lawrence said that Forest tent caterpillars may be found clumped on a tree trunk, and can be killed by brushing them into a bucket of soapy water. For Eastern tent caterpillars, a stick with a nail crosswise through its end can be used to pull the tent and caterpillars into the bucket. “It’s best to do this in early morning or evening when most caterpillars are in the tent,” Lawrence said.
Next fall and winter, look for the hard, black egg masses encircling pencil-diameter branches and scrape or prune them out and destroy them before spring.
Lawrence said that as large as the caterpillars are now, they will soon be done feeding, so in most cases it’s not worth spraying insecticides.
“It’s too late for the biological insecticide Bt (Bacillus thuringiensis) to be effective,” Lawrence said, “so insecticides would have to be chemical, and even those are less effective once caterpillars are over one-inch in length.”
The good news for the trees that are heavily defoliated after being attacked by tent caterpillars is that they should grow a new set of leaves.
“That’s another stress on trees, so particular care should be taken to limit other stressors, like drought,” Lawrence said. “But most healthy trees should tolerate defoliation at this early point in the growing season.”
Where tent caterpillars are out in huge numbers, they can quickly strip the leaves from their host trees, especially since many of their hosts don’t yet have a full complement of leaves. When caterpillars run out of leaves on one tree, they crawl across the ground to find other acceptable trees. When caterpillars are done feeding, they will again migrate cross-country to find protected places to spin cocoons and go into the pupal stage.
“So some of the migrators you see may be done with their leaf damaging already,” Lawrence said. “There is only one generation per year, so they will be done for the year soon.” Tent caterpillars’ cocoons are about one inch long, yellowish or white, silky, and football-shaped. After metamorphosis, they turn into moths.
For more information, call Lawrence at his office in Columbia at 573-815-7901, or email Rob.Lawrence@mdc.mo.gov.