Edit: This post was recently included in the 180th edition of Friday Ark, a weekly blog carnival focusing on animals of all sorts. You can check out the full edition at The Modulator.
One of the downsides to learning things yourself using the internet or reference books as your guide is that it’s pretty easy to mis-identify something based on poor photographs, incomplete descriptions or information, or just vague or ambiguous wording, particularly if you have a notion about what you’re expecting. In one of the posts I did mid-January, about fungus in the woods in winter, I mentioned a large, creamy, fuzzy mass I observed on the trunk of a tree that I identified as a slime mold. Well, Jennifer over at A Passion for Nature corrected me on this by (correctly) suggesting that it looked like a gypsy moth egg mass.
I went back yesterday to the same area and had another look at it. The particular one I photographed still looked and felt (to my frozen-numb hands) like a cattail thwack with no particular distinguishing characteristics (I didn’t want to try taking it apart because I don’t like to disturb). However, upon closer investigation, I started noticing more of these fuzzy blobs on nearby tree trunks, pretty much all within a few feet of the ground. Some of them had much more obvious visual characteristics that may have led me to the eggs conclusion if I’d seen them first. In the above and the first photo you can actually see the individual eggs wrapped up in all the little hairs that create the fuzzy mass (I think the first photo may actually be hatched eggs from last year? It’s hard to tell, but the dark spots are very pronounced). The hairs are made by the female moth as she’s laying her eggs, and are hypothesized to protect the eggs from potential rodent and avian predators by discouraging them from getting the hairs in their face and nostrils and irritating the skin.
Gypsy Moths aren’t native to North America (like a lot of common wildlife). Rather, they were brought over to Medford, Massachusetts in 1869 by French astronomer Leopold Trouvelot, who also had an interest in insects and was hoping to breed a sturdier, more productive silkworm. Well, like often happens, the moths escaped and it didn’t take them long to settle into the new landscape. They’re now found into eastern Canada as far north as Maine and the Maritimes, as far south as northern North Carolina, and currently west into mid-Wisconsin. When you consider the size of the insect in question, it’s a pretty good area to cover over that period.
The moth’s dispersal is also made more interesting by the fact that the female moth, the recognizable white Gypsy Moth, can’t fly. When she emerges from her pupa she’s full of eggs and way too heavy to get airborne. Male moths (which are brown) can fly, and will travel long distances to reach a female, which they detect using the broad, fluffy antennae that only males possess. These antennae are specially designed to pick up the pheromone molecules released by the female when she emerges. Near a couple of the egg masses I found pupa cases left from the female when she emerged. The cases also have hair tufts that presumably protect them the same way the hairs in the egg mass do.
Still, if the females aren’t moving, then the eggs are going to be laid near where the female emerges, which also doesn’t help much with dispersal. Instead, dispersal is carried out by the caterpillars (weird, eh? The only ones without wings). Caterpillars, during the course of their feeding, climb to the top of the tree and then spin a line of silk which they use to “balloon” on the wind over to the next tree. I can’t imagine this taking them very far, so it would be a very slow dispersal.
This photo (used with permission) is of a female caught in the act of laying an egg mass in late summer. She was found inside a porta-potty, so I can’t imagine the caterpillars would have much to eat when they hatch, but I gather Gypsy Moth females aren’t too particular about where they lay their eggs. The larvae will feed on up to 500 different species of trees, but particularly favour oak. Most of the egg masses I came across were on rough-barked tree species, primarily Black Cherry. Caterpillars hatch from their eggs in early spring, late April into early May. They feed on tree leaves and can be a severe pest in some areas where they completely denude trees of their foliage, particularly since a single egg mass can contain up to 500-1000 eggs. In late June to early July they begin to pupate, and emerge as adult moths after a couple of weeks. Females lay egg masses shortly after emerging, and adults will never eat. Adults die shortly after mating, and the species overwinters in the form of these egg masses.
It’s funny how once you know to look for something, it suddenly seems to jump out at you everywhere. Now that I’m aware of these and what they are, I’ll be keeping my eyes open for them on future walks.