Local outbreak continues, little threat to humans
If it seems like every spongy moth caterpillar in the Highlands hatched this week, it’s because they probably did.
“That was a boom day,” said Clive Jones of the Cary Institute in Millbrook, referring to the spongy moth caterpillars — formerly gypsy moths — first spotted on May 1. He said a similar mass hatching occurred the previous week in Gardiner, and that the Cary Institute’s campus was seeing its first outbreak of what he called “spongies” since the 1990s.
The caterpillars prefer oak leaves, so the same conditions that trigger oaks to start budding — a certain number of consecutive days above a certain temperature — also trigger the caterpillars to hatch. “Many insects have managed to get themselves synchronized to when food is available,” Jones explained.
If the blanket of caterpillars is disconcerting now, brace yourself. Soon the caterpillars will start “ballooning,” or hanging from branches by a silk thread and letting the winds gently carry them to new trees. Jones said that because the hatch was so large, the competition for feeding spots will be fierce, which means a lot of floating caterpillars.
“It’s irritating when you walk through a cloud of them, but at that point they’re not particularly problematic,” said Jones. The caterpillars do not bite, but their tiny hairs can cause a reaction that feels like a bite. Jones suggests wearing long sleeves and long pants for the next few weeks, and a wide-brimmed hat.
“There’s going to be caterpillar crap falling everywhere,” he said. The technical term is frass.
The Cary Institute hosts a page at bit.ly/cary-spongy that lists strategies for dealing with the outbreak, besides hiding indoors. Since most of the spongy egg sacs have hatched, disposing of them is a waste of time. Burning the sacs with a blowtorch is a popular method but New York State’s burn ban is in effect until May 14.
To protect a tree from the caterpillars, tie a band of burlap around the trunk. The caterpillars will fall to the ground and can be swept up and placed in a bucket of hot soapy water and composted the next day. Because of the prickly hairs, Jones recommends wearing latex gloves.
Wrapping a sticky band around trunks can ensnare beneficial pollinators. There’s also the microbial insecticide Bacillus thuringiensis (Bt), but you need a license to apply it. Jones said anyone with that license in the state is already booked for the season.
Squashing individual caterpillars won’t make much of a difference, Jones said, but “some people gain a certain degree of satisfaction from smashing a caterpillar. I’m not going to take that pleasure away from people.”
The final option is to pray for rain. Spongy moths have two natural predators: white-footed mice and the fungus Entomophaga maimaiga. When the outbreaks get to be as big as they are, the mice can’t eat enough to make a dent. The fungus needs lots of wet, humid weather over the next six weeks without having too many days in the 80-degree range.
“It’s just like growing mold in your basement,” said Jones. The fungus infects the caterpillars with spores that kill them, and as the caterpillars decompose the spores spread to new hosts.
The good news is that there shouldn’t be much permanent damage. There may be a lot of defoliation in the Highlands this spring and summer, as there was last year in the first season of the outbreak, but most hardwood trees will recover.
Eventually, the caterpillar population will get so big that it will get stressed trying to find enough food, weakening their immune system and making them more susceptible to the fungus. That will lead to a population crash and the end of the outbreak.
Whether that happens this year or next year is unknown. For those who would like to learn more, Jones is planning a public walk at the Cary Institute on June 8 to talk about the outbreak. “It’s for anyone who wants to come and have frass fall on their head,” he said.
Year 3 and I’m losing my mind.
On a positive note, mice and fungus are not alone in predating on “gypsy moths.” On Canopus Hill, I recently spotted a pair of yellow-billed cuckoos, which specialize in the caterpillars and regurgitate a pellet of the hairy spines. Many other birds eat them, as well.
I love nature, but you critters are testing me. [via Facebook]
Not much permanent damage? As the spotted lanternfly defoliates the same tree over and over and the tree keeps working to push more out, the tree will die. Wrapping any-thing around its trunk doesn’t help much if the bugs are already in the tree. They will not come down until they die, fall or turn into a cocoon.
This is very bad for hardwoods and now the spotted lanternfly is moving into anything else. I’ve seen them destroying arborvitaes, purple plums — you name it. We need a cold, snowy winter, which we haven’t had in two years, or many more trees will die.