Moths of Winter : Bad news for next spring

By Beth Sullivan

We had an incredibly mild stretch of weather these last weeks. Several days were warm enough to allow small gnats and flies to swarm and even a few butterflies to roam during the day’s sunny warmth. Out in the woods and thickets, a few lingering warblers and flycatchers got lucky enough to find sustenance later than usual.

Invasive Winter Moth

There is a down side. Several nights of warmth created perfect conditions for the emergence of the Winter Moth. This invasive, non-native, insect has been around for a while, but seemed to burst into our awareness last spring when leaves on numerous species of trees emerged deformed, eaten before unfurling. Ornamental and fruiting trees had their blossoms devoured before opening. Without the blossoms there was no pollinating and no fruits this past fall. Crab Apples, some Cherries, and Dogwoods never carried full loads of berries, and this Autumn the birds lost out.

Caterpillars go dormant in the soil in masses, then pupate to emerge at this time of year.

When leaves emerge in Spring, they are already damaged by the larval Winter Moth.

Swarming Winter Moths

The life cycle of these moths is only now being understood. Right now the moths are flying in clouds and those are only the males! They are small, boring and light brown. They usually land with wings spread, but they may be held together, which is unusual for moths. The females have small non-functioning wings, and when they emerge from the soil, they climb up the base of the trees where they are found by the males and mate. They then crawl up the tree to lay their egg masses in cracks and crevices in the bark, close to leaf buds. The moths die and the eggs overwinter. The caterpillars emerge very early and begin eating the leaves and flowers while in bud. They are not terribly fussy, and they will feed on many tree species, from mighty Oaks to Blueberries and garden plants. The affected Oaks have produced very few acorns locally, in an otherwise huge acorn year.

Gypsy Moth egg masses are easy to spot now and can be scraped off bark.

When the caterpillars are done feeding, they drop to the ground where they remain dormant through the summer, to pupate in the fall. I discovered masses of these dormant larvae just under the leaf litter as I did fall clean up in my gardens. They emerge, to continue their cycle, after a hard frost period and rewarming in mid November and December.

Male moths, like these brown Gypsy moths, must fly to find the more inactive females waiting on tree trunks.

The trees that had significant leaf damage were stressed for the entire season. Some were able to send out a second set of leaves later, but that is an enormous expenditure of energy. Then we had the later summer drought and heat which literally dried out the tender leaves well before they were due to fall.

Moths are attracted to lights and swarm on warmer evenings.

Check your trees

Until entomologists and landscape contractors can better understand the full life cycle, there may be no way to interrupt the onslaught. If you can check the bases of your trees now, it may be possible to find and destroy the females before they ascend the trunk. Smaller trees in the home landscape can be treated with a horticultural oil or insecticidal soap to kill the eggs or larvae early on. I go out and squash them by the hundreds, even thousands, when they collect by lights I leave on purposely to attract them. But that is a drop in the bucket. We cannot protect the entire forest. For now we hope that some natural predator or disease will be found that will stop their march.

Several years of defoliation and drought will kill many woodland trees.

Several years of stress from infestation and drought, may cause trees to die and we might expect to see large areas affected like after the Gypsy Moth invasion of decades ago. A disease evolved to help kill off Gypsy Moth caterpillars. Their egg masses are easier to find on tree trunks and can be scraped off. But those moths also reappeared last year in greater than expected numbers.

Seems to be another round of bad news for our already stressed woodland habitats.

Photographs by Beth Sullivan