Due to the outbreak of Gypsy moth (Lymantria dispar) populations in the Great Lakes region this year, we are seeing unprecedented numbers of overwintering egg masses on just about any kind of tree, fence or outdoor stationary structure. We even found an egg mass on the wheel of a stationary vehicle….you can see how this insect earned its common name. There is a good chance that many home owners will find the same egg masses on the trees around their homes this year, which may help put this issue in perspective.
Even though Gypsy moth do not typically feed on the foliage of fir (Abies spp.), their egg masses can be found on fir, hemlock and pine tree trunks and the lower sides of branches this year. Partly due to the exceptionally high populations and also because adult female Gypsy moths cannot fly and disperse once they emerge. However, larvae do feed on spruce, which is less frequently purchased as a cut tree but a much more common egg mass host.
Here’s the GOOD NEWS: Gypsy moth egg masses will not likely be hatching in your living room this December. The embryos take weeks to develop under warm spring conditions, and don’t seem to be able to complete their development when brought in the home for a few weeks. I couldn’t find any evidence that this has ever happened so I did my own experiment. I took some egg mass samples on November 11th that I have been holding at room temperature to observe the tiny wasp egg parasitoids (see below) and… at the 4-week mark (28 days), the Gypsy moth larva started to hatch from their eggs.
This means that if you bring a live Christmas tree with a Gypsy moth egg mass on it inside the house on Saturday, December 5th, you won’t see much in the way of egg hatch if you put your tree out by January 1st. Even if you keep your tree a few extra days, larval hatch takes place over several days and chances are you won’t even see them – they are only 3 mm long – they will remain on the tree and will likely die of desiccation.
In my samples, the parasitoid wasps keep emerging, breeding and laying their eggs inside the Gypsy moth eggs! These wasps will be an important form of biocontrol, helping to reduce the number of successfully hatching larvae next May.
Just to confirm, I will be doing weekly sampling of egg masses throughout December, until Christmas and watch them for any hatching activity.
If your customers are still concerned, just lay the tree down on its side, preferably outdoors in good daylight, and examine the trunk and branch undersides for brown, fuzzy eggs masses. Scrape any egg masses lightly from the tree, catch them in a container, for disposal.
However, if you find a brown egg mass that is NOT fuzzy and looks more like it is made from foam insulation like in the photo above…..you might want to prune off the twig that it is attached to and put it outside. It is mostly like a Praying Mantis (Mantis religiosa) egg mass, and those little guys MAY HATCH in your living room this December. Now, they will most likely eat each other and then die of starvation on the tree. That’s because they are natural predators of other insects. To save them from this fate, place praying mantis egg masses deep inside the foliage of an evergreen out in the garden. There they will be able to serve their important ecological role in the landscape next spring and summer 🐜