It’s that time of year again: fir tussock moth season.
If you’re in Florida and have ventured outside lately anywhere with oak trees, you may have encountered a unique caterpillar — or hundreds.
The ubiquitous insect undergoing its annual outbreak is the fir tussock moth, or Orgyia detrita for those who prefer scientific nomenclature. The creatures, which are abundant throughout the state, can cause skin irritation, so read up before rounding them up or otherwise touching them.
“In my experience, it’s always happening in this part, North Central Florida, at this time of year. Late March and April, we get big numbers of these things,” said James Hayden, a taxonomist with the Florida Department of Agriculture and Consumer Services Division of Plant Industry.
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How to identify fir tussock moth caterpillars
Fir tussock moths are found primarily in Florida, as well as on the Gulf Coast and in some East Coast states.
The other two Orgyia species found in Florida are the white-marked tussock moth (Orgyia leucostigma) and the less common definite moth (Orgyia defineta). Both have a presence across the eastern United States beyond Florida.
Fir tussock moth caterpillars are identifiable by their red heads, two black “hair pencils” that look like antennae, a dorsal hair pencil, four prominent yellow or white tufts on their backs, and orange spots all over.
There are two phenotypes, one lighter and one darker. Many have bright yellow hairs, while some have white or off-white hairs.
White-marked tussock caterpillars are similar in appearance but have a lighter body color and yellow spots. Definite tussock caterpillars have yellow or tan heads and a pale body.
Why are there so many?
“Oak trees are their primary hosts, so if you’ve got oak trees in the area, every year this time of year, it’s prime tussock moth caterpillar time,” said Adam Dale, an assistant professor in the Entomology and Nematology Department at University of Florida’s Institute of Food and Agricultural Sciences.
The moths spend the winter as eggs, which hatch as the weather gets warmer. Most eggs hatch by the end of March, so late March and early April are peak times to see the caterpillars, which have been undergoing development by eating oak leaves and are preparing to spin a cocoon and pupate.
The further south and warmer climate, the earlier they may appear.
“Years like this year when they really seem to have exploded, they’ll drop out of the trees and wind up all over everything,” Dale said. “Even in years when they’re not super dense, after the caterpillars have almost finished developing, they’ll leave the tree, so they’ll drop from the tree and then climb onto other structures and surfaces like porches and windows and shutters and anything on your house.”
It’s difficult to predict how prevalent the caterpillars may be from one year to the next, but temperature and precipitation in fall and winter can play a role.
“They have one generation a year, so after the caterpillars finish their development around this time, we won’t see them again until next year this time, but there’s always ebbs and flows of how abundant they are in any given year,” Dale said.
Will there be this many moths?
Dale and Hayden say you won’t see as many moths as you have caterpillars when they emerge from their cocoons in mid-April and early May for multiple reasons.
First off, the caterpillars have predators.
“A lot of things will also eat them,” Dale said. “The predominant things are beetles and birds and wasps, like paper wasps that you would see on the side of your house. Those adults are out snatching up caterpillars.”
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Secondly, the brown male moths are not as flashy as the caterpillars, and the females are difficult to spot.
“The three species of Orgyia, the females are entirely wingless, and they look like little balls of gray fuzz, like a little cute dust ball with a little moth head,” Hayden said. “You might be lucky enough to see one sitting on a house calling for a male, and then he’ll fly up and they’ll mate and she’ll dump the eggs where she’s sitting.”
The female will lay eggs on her cocoon and then dies.
Are fir tussock moths dangerous?
Both the cocoons and caterpillars can be irritating to touch with bare skin.
“On the sixth and seventh abdominal segment right in the middle, you’ll see two orange circles, and those little orange circles are actually tassels that produce a defensive secretion,” Hayden said.
The tussock moth caterpillars are not in the stinging caterpillar category like saddleback and puss caterpillars, but they do have stinging hairs that can be of danger if touched, particularly the four tufts, or “tussocks,” on their backs, Dale says.
“Those are the stinging hairs, and if you were to rub those with your skin, that could cause some irritation, and that’s what people are concerned about,” he said. “There’s a whole range of reactions to that, like some people like me have no reaction to it and others might have a breakout, a little rash on their skin.”
The cocoons are made up of the hairs, so they can have the same irritating effect. They are white to tan and fuzzy in appearance, often stuck on the sides of houses and other structures.
What can I do about them?
If the presence of the caterpillars or cocoons is overwhelming, there are a few tactics that can help.
“You can sweep them into soapy water, or you can suck them up with a shop vac, basically physically remove them from the situation and dispose of them,” Dale said. “That’s the best thing you can do in terms of them coming into your house or in places where you don’t want to be exposed to them.”
Cocoons can also be vacuumed or scraped into a container.
Even though homeowners are often concerned about the caterpillars defoliating trees, Dale only recommends applying insecticides in dire or high-risk situations.
“Oak trees support all sorts of caterpillars, and that’s just a good food source, but they don’t damage oak trees,” he said. “When you (apply insecticide), you’re also controlling all the hundreds of other caterpillars that feed on oak trees, and those support birds and all sorts of other wildlife.”
A justifiable situation might be an oak tree at a daycare or area where children frequent. However, insecticides applied to the tree won’t do much unless applied in winter or early spring in anticipation of the eggs hatching because the caterpillars have mostly completed their development.
In other words, since the caterpillars will only be around another couple weeks, the best option may be to admire them from a distance and enjoy the weather.
“I think they’re really beautiful little caterpillars,” Dale said. “They’re really cool. I always get excited when I see them just because it means spring is here.”
Contact reporter Danielle Johnson at email@example.com.