Nature News: Look for the elusive praying mantis egg cases

Nature News: Look for the elusive praying mantis egg cases

By Susan Pike

While searching through a jumble of clay pots, I had abandoned by the side of the garden I found a praying mantis egg case secured to the side of a pot. I don’t know anyone who doesn’t think praying mantises are awesome. They are large, charismatic insects with an intense, predatory stare. Interestingly, there are a few misconceptions about these animals, misconceptions that definitely add to the mystique.

Growing up I had always been told that praying mantises are endangered and that it was against the law to kill them. This is completely untrue, in fact, the two species of praying mantis that you’ll find in New England are not even native to this area. The one you are most likely to find in your backyard is the European praying mantis (Mantis religiosa), found all over New England (though southern Maine, New Hampshire and Vermont are at the northern edge of their range)) The European praying mantis was introduced around 1900, either by accident, arriving on nursery plants, or on purpose by gardeners. Chinese praying mantises (Tenodera sinensis) were introduced a few years before the European praying mantis and are only found in southern New England. These are huge – getting up to 4 inches in length. They are famous for their ability to hunt small reptiles, rodents and hummingbirds (praying mantises have been recorded catching and eating birds in all continents except Antarctica!). The only Chinese praying mantises I’ve seen up here came from an egg case I bought at the garden shop (praying mantis egg cases are sold as a natural pest control). Given that these are non-native species and that you can buy the egg cases in garden shops argues against their mythical endangered species status.

Another myth, the idea that praying mantises are beneficial insects, the idea that you can use praying mantises as a natural form of pest control in your garden seems like a good one. I certainly bought into the idea. We bought an egg case, left it on the kitchen counter and woke up one morning to hundreds of tiny (very cute) praying mantises trying to make a break for it out the kitchen window. We learned our lesson and never brought subsequent egg cases inside. Is this really a good idea? Praying mantises do kill all sorts of insect pests, but they just as readily prey upon beneficial insects, pollinators like butterflies and bees. Do you really want to release an army of top predators into your garden? This same logic applies to using dragonfly larvae to control mosquitoes in your pond – the ones you buy are not native and shouldn’t be used.

The myth that I really hate to debunk is the idea that the female praying mantis bites off the head of her mate after copulation and eats him. Most praying mantis species do not do this. Of the species that have been known to do this, females cannibalize their mates on the order of 13 to 28 percent of the time. It turns out black widow spiders don’t usually do this either.

I have a great book called “Tracks and Signs of Insects and other Invertebrates” (by Eiseman and Charney) that describes the praying mantis egg case I found in my garden. “Mantises deposit eggs in oothecae that contain up to several hundred eggs and are made of a light, frothy substance, which the female shapes as she deposits it. A mantis ootheca is more or less oval, and down the center is a series of overlapping scales concealing tiny corridors that lead to a central chamber. The young emerge through these corridors, all at once in the spring and because of the scales, the external change to the ootheca after emergence can be very subtle. A small tassel of white silk may dangle from the central strip, made up of threads from which the nymphs hung when they first emerged.”

You are unlikely to see a praying mantis in your garden. There aren’t that many around and they are very well camouflaged. So, look for the egg cases, obvious indicators that these exotic little killing machines are stalking through your undergrowth.

Susan Pike, a researcher and an environmental sciences and biology teacher at St. Thomas Aquinas High School, welcomes your ideas for future column topics. She may be reached at [email protected].