Luna Moths: As Lovely as a Moonlit Night

Luna moths are insects that I think we can all agree to admire. One of the largest moths in the eastern United States, it has a wingspan of nearly 4½ inches. Attracted by porch lights (possibly mistaking them for the moon) they are a welcome visitor to any nature-friendly home or garden. 

The first batch of this year’s luna moths have already come and gone. However, if we are lucky, we’ll have a chance to see their kids when they grow up and make their cameo as moths in late July or early August. These second-generation luna moths will lay eggs that will get as far as the pupa stage. They spend the winter as pupae in cocoons, nestled in the leaf litter. If you don’t feel like raking all the leaves in your garden this fall, you now have a great excuse: “I’m saving the luna moths!” These overwintering adolescents will emerge as adults early next summer.

Adult luna moths only live for about a week and do not eat. All the adults aspire to accomplish is to find a mate and/or lay eggs and then expire. The caterpillars feed on a variety of trees, including white birch, sweet gum, hickory, sumac and walnut. The caterpillars look superficially like a tomato hornworm, minus the horn. They are well camouflaged and feed up in trees, so don’t feel bad if you have never seen one.

You can tell the male from female moths, since the males have bushier antennas than the females. The males use their antennae to follow the pheromone trail of females. Since they fly in the dark, they need to rely on their sense of smell rather than by vision, like day-flying butterflies.

Anecdotal evidence indicates that luna moths might have been more common in the past. To my knowledge, long-term records have not been kept for this area so it’s hard to know. Please feel free to leave a comment if you have seen a change in the luna moth population of your favorite local habitat. Fortunately, luna moths are neither rare or endangered within the ranges that they have been historically observed. 

Like many of our native species, luna moths are facing some strong headwinds. A small parasitic fly called Compsilura concinnata was introduced from Europe in an attempt to control invasive gypsy moths. The parasitic flies were intentionally released for an 80-year span, starting in 1906. So far, the flies seem to be doing a better job of killing native and charismatic friends, such as luna moths, giant silkmoths and royal walnut moths.

Researchers in a 2003 study set out luna moth larvae in a forest that was not yet invaded by gypsy moths. As many as 60 percent of the luna moth caterpillars were parasitized by the introduced parasitic flies. It is not yet known if the flies have had a significant impact on luna moths in the Lehigh Valley, but it’s worth investigating. These errant parasitic flies illustrate the reason why researchers are now very careful before releasing new and exotic predatory insects into the wild.

Anything we can do to preserve forested areas will help the luna moth. Recent research at the University of Delaware has shown that the luna moth’s very favorite food is American sweetgum followed by black walnut. The researchers also found that they were not very fond of non-native plants. They not only require a forested habitat, but it also matters what is growing in it. 

Luna moths were apparently named for the crescent-shaped markings on their wings. I think they would be a good mascot for the new Luna Park at Coney Island. Interestingly, the term "Luna Park" has been equated with amusement parks since 1903. If they adopted my idea, Luna Park would probably run into trademark issues with the makers of Eszopiclone (aka Lunesta), a wildly popular sleeping medication. I think an organism that is most active between the hours of 11:00 p.m. and 2 a.m. is an odd choice for promoting a sleeping pill, but maybe I’m missing something.  

This work by Marten Edwards is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.