What’s up with those caterpillars everywhere?

If you spend any time outdoors at all these days, a caterpillar—or two or three—will probably end up crawling on your arm, your head, your shoe or your car.

According to local experts, these caterpillars that come in shades of gray, yellow and other colors are future tussock moths and they are abundant this year.

The moths that are best known for their attractive larvae, are leaving their host plants and searching for a place to start to cocoon, according to University of Florida Entomologist Donald Hall, who wrote the book on caterpillars along with Lyle Buss, insect ID lab manager at UF.

Oak trees are among the most favored host plants for the caterpillars.

The one to one-and-a-half-inch long caterpillars are characterized by “hair pencils” of black setae that extend forward. And they have four dense tufts of hair called “tussocks” on the back plus a fluffy tuft that projects to the rear of the tail.

“They are common most years,” Hall said about the creatures. “But their populations vary significantly from year to year due to weather conditions and to prevalence of their natural enemies and diseases.”

According to Hall, there are three species that are found in Florida: “Orgyia detrita (the fir tussock moth) is the most common of the species in Florida, followed by Orgyia leucostigma (the white-marked tussock moth) and finally Orgyia definita (the definite tussock moth), which is rare in Florida.”

One thing to be aware of according to Hall is that these caterpillars do have a “sting.”

Hall has a photo on his website of the results of pressing a caterpillar’s tussocks against his wrist. In Figure 26, you can see the pruritic welts and erythema that results from rubbing hairs from the dorsal tussocks of the tussock moth, Hall reports. And people have varying degrees of reaction to coming into contact with venom.

In his research, Hall found that some homeowners develop dermatitis from contact with the cocoons while removing them from surfaces or items around the yard.

“Hairs in the cocoons retain their urticating capability for up to a year or longer,” he reports.

The caterpillars are right on time according to Hall’s findings that the “caterpillars reach maturity and wander in search of sites to spin their cocoons in early April in Florida.”

And Hall’s research states that adults emerge from mid-April to early May.

“The flightless females remain on their cocoons and release a sex pheromone to attract males,” according to Hall’s website. “After mating, the females lay a mass of eggs directly on the cocoon and cover them with a protective covering.”

Forest entomologist John Foltz, UF emeritus associate professor in the Department of Entomology and Nematology, said he has a hypothesis about why there seem to be an “outbreak” in caterpillars this year.

“The periodic outbreaks depend on several successive springs in which hatching from the overwintering egg masses is exceptionally coincident with the flushing of new leaves on their favored host trees,” he reported. “Most years there is an extended hatch and an extended flush so that only a small proportion of the new larvae successfully find and establish feeding sites.

“Occasionally, however, larval establishment is way above average for two or three years, and the populations explode to detectable and sometimes annoying levels. After several years of high host populations the natural enemies catch up, reduce the generation survival, and the tussock moth populations collapse.”

Foltz suggested a quick science experiment for those interested in learning about the Orgyia detrita, the common one generation per year tussock moth, here in Central Florida.

He said to collect and cage dispersing caterpillars. “Most will spin cocoons within a few days and moths may emerge two weeks later. There are also several species of parasites that kill their pupal host and emerge at this time. The wingless females that emerge sit on their cocoons and during the night produce a pheromone to attract the winged males.

“There are lots of things to learn for the inquisitive mind,” he said.

Male fir tussock moth on white background
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