Gypsy Moth

The last couple of times I’ve walked in the Big Woods the forest has looked like this –

That wasn’t November it was early June and a view of the hillsides revealed that extensive areas were bare of leaves –

The cause was these caterpillars –

Not just one caterpillar but many thousands, perhaps millions, to each and every acre – here climbing the trunk of a white oak in search of additional leaves to eat –

They’re the caterpillars of the gypsy moth (Lymantria dispar) an insect native to Europe and accidentally released in Massachusetts in 1869, from there it has spread extensively wherever its favored food species (oak, aspen, apple and others) are abundant.

In 2021 the Entomological Society of America (ESA) decided to change the insect’s name from gypsy moth to spongy moth since the name, gypsy, could be considered offensive to the Roma people (often called Gypsies). Gypsy moth has been the insect’s name for over 150 years and so it will remain here until the ESA changes any other moth names that could be offensive to someone (e.g. The German Cousin, The Hebrew, Finnish Dart, the Setaceous Hebrew Character, a large group called Quakers and others).

Back to the Big Woods: There are gypsy moth caterpillars of many sizes, some almost ready to pupate and others needing more time to feed and grow. The younger caterpillars may well starve as most of the trees’ leaves have already been eaten or fallen to the ground as scraps –

Larger, older caterpillars will soon enter their pupal stage where they will transform into adults –

Adult females are white moths, flightless due to the heavy masses of eggs they carry and will soon lay as tan spongy masses –

Male gypsy moths are tan and fly about searching for females with which to mate. They find females by the scent (pheromone) the females emit and is detected by the males’ feathery antennae –

The tan egg masses contain the eggs that will produce next year’s caterpillars. A number of tiny wasps parasitize the gypsy moth eggs, helping to control the population. The few species of birds that eat hairy caterpillars feed on those of the gypsy moth as do white-footed mice. The larvae of several introduced species of parasitic flies feed on gypsy moth caterpillars as does an introduced fungus; caterpillars killed by the fungus hang in a characteristic “J” shape –

But the parasites, predators and diseases don’t always keep gypsy moth populations in check, every 10-20 years there’s an explosive population increase such as we’ve seen this year. What of the trees that have been stripped of their leaves? Almost all will survive and grow new leaves in the next several months; if the trees are defoliated next year, roughly 30% will die; a third year of defoliation will probably kill 60% of the trees. But perhaps the predators, parasites and diseases will succeed in killing enough gypsy moths that the trees will not be defoliated for a second or third year – time will tell.

Note – Introduction of several species of flies to control the gypsy moth has had an unintended consequence,

they also parasitize our most beautiful large moths (including the luna, polyphemus and promethia) with devastating consequences to their populations.