In A WormHole

Crazy caterpillar invasion plagues Texas: But is the mad worry over little worms overblown?

Crazy caterpillar invasion plagues Texas: Is the worm worry overblown

Photo of forest tent caterpillars on tree
Slender with fuzzy sides, forest tent caterpillars congregate en masse on the side of a tree south of Dallas. Photo by Heather Raines
Photo of safe tent worm pesticides
For plagues of tent caterpillars that threaten to damage a stressed tree, inexpensive and safe organic treatments beat the cost of a pest control service. Photo by Marshall Hinsley
Photo of Marshall Hinsley with a pump sprayer
Marshall Hinsley prepares a handheld pump sprayer for low-cost home treatments. Photo by Allee Brand
Photo of forest tent caterpillars crawling up a tree
Because of the congregating habit of tent caterpillars, encountering a cluster of them as they ascend a tree can be alarming. Photo by Heather Raines
Photo of forest tent caterpillars on tree
Photo of safe tent worm pesticides
Photo of Marshall Hinsley with a pump sprayer
Photo of forest tent caterpillars crawling up a tree

If you follow gardening pages online, you've probably seen photos posted this week by perplexed homeowners showing armies of caterpillars swarming tree trunks across Texas.

The caterpillars are fuzzy, about an inch and a half long and dark in color, with a spotted pattern that runs along their backs. If they traveled solo, they might go unnoticed. But their tendency to cluster into a mass, covering tree trunks, the eave of a house or an entire electric transformer on top of a power line, makes for an alarming sight, prompting a flurry of speculative comments about their identity and the damage they do.

Are they army worms, web worms, bag worms or tent caterpillars? Do they spin a web around the whole tree and kill it, or do they just eat the leaves?

 Insect researcher Joshua Huckabee says the caterpillars feed on the young, budding leaves of their host plants, but they are no threat to garden crops.

Do you take drastic measures and spray them with Windex, oven cleaner or worse? Do you cover them in plastic, light them on fire or leave them alone?

You can probably relax and not do anything, says Joshua Huckabee, an insect researcher in Temple, Texas.

"These are forest tent caterpillars," Huckabee says. "Malacosoma disstria is their scientific name. They don't sting, and spraying them isn't really necessary. They'll be moths in a few weeks."

Huckabee says the caterpillars feed on the young, budding leaves of their host plants, but they are no threat to garden crops. "They could pose a threat to young or unhealthy trees, and they will often defoliate trees," he says. "But large, healthy trees usually leaf out again with no problems."

They do favor oaks. "They primarily eat oaks and sweet gum in the southern states," he says. "They may also feed on plum and cherry trees."

The caterpillars get their name because they form a tent of webs in the nodes of tree branches. The tent helps the caterpillars moderate their temperatures in the unpredictable climate of early spring. The tent is warm on the sunny side and cool on the shady side, so the caterpillars move to keep their body at the right temperature.

When they leave their tent to feed elsewhere, they tend to travel in a pack, leaving a pheromone trail to mark their route between food sources and their tent — making for an unsettling display to anyone unfamiliar with their ways.

"They're very gregarious," Huckabee says. "I do not recommend spraying pesticides by any means, because they may kill other beneficial insects in the area. If you see the masses moving up the trunk, they can be removed manually since they stay together in groups. Egg masses can be removed during winter pruning to prevent more caterpillars the following spring."

 There's been a population boom this year — a bonus to the birds, frogs, lizards and other animals that feed on them.

There's been a population boom this year — a bonus to the birds, frogs, lizards and other animals that feed on them.

"These caterpillars have lots of natural predators, including parasitic wasps and flies, beetles, birds, frogs, nematodes, viruses, and bacteria," Huckabee says. "It's hard to say why they're so numerous this year. Forest tent caterpillar outbreaks have a cycle: one or two years of outbreak every six to 16 years. But the recent outbreak in Texas could possibly be attributed to last year's mild winter."

Huckabee says the caterpillars will hang around for a few weeks, then pupate in June, after which they'll emerge from cocoons as small, brown moths that sport fuzzy antennae. Therefore, their status of pest will resolve itself, with no action needed except in extreme circumstances.

Homeowners who fear that any tree previously stressed by drought or insect damage is vulnerable may keep the caterpillars in check by releasing wasps in the area of the tree or using an organic caterpillar control. Products containing Bt may work on young caterpillars; sprays containing the organic insecticide known as Spinosad may be more reliable.

Sprayed into the tents with a forceful stream from the wand of a handheld pump sprayer, these remedies can save homeowners and property managers from being hit with a pricey bill from a pest control service.

But Huckabee has no plans to spray. "I find the caterpillars to be beautiful and interesting," he says. "I think much of the alarm over them is fear based. But to me, there's no such thing as a bad insect."

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