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March 2011 cover image The Best of Texas, Naturally!

Wild Thing: Hanging by a Thread

Cankerworms descend by the thousands each spring.

By Sheryl Smith-Rodgers

Like many brides, the young woman worked for months, planning every detail — like colors, decorations, flowers and music — so her outdoor wedding in early spring would turn out picture perfect.

On her “I do” day, however, nature intervened. “Thousands of cankerworms streamed down from the live oaks,” recalls Briana Fuchs, who catered the March wedding near Blanco. “We spent an hour sweeping them down with brooms!”

Fuchs and her horrified bride (along with most folks) despise the drab, hairless caterpillars that devour foliage and drop from trees on silken threads. What’s the point of such a pesky insect?

“They provide food for arthropods and birds,” says Wizzie Brown, an entomologist with the Texas AgriLife Extension Service. Spring cankerworms (Paleacrata vernata) overwinter in the soil as pupae and emerge in early spring as small gray moths. Oddly, females — long-legged and chubby — lack wings. In search of males, they climb up oaks, elms, hackberries and other deciduous trees, where they mate and lay egg clusters on bark.

In a few weeks, tiny caterpillars hatch out and gorge on leaves for three or four weeks. Populations vary yearly, but occasionally, huge numbers can strip a tree bare. Then the inch-long larvae rappel to the ground, dig a hole and pupate until spring.

As their name implies, fall cankerworms (Alsophila pometaria), a similar species, emerge as adults after summer. Wingless females mate and lay eggs that overwinter until spring.

Another common name — inchworm — refers to how both species crawl. Because their middle sections lack legs, cankerworms arch their backs, extend their front legs and then draw up their back legs behind them..

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