Regional Gardening Reports :: National Gardening Association

In the Garden:
July, 2008
Regional Report

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Praying mantids are a curiosity to us but deadly to many insects.

Mind Your Mantids

With its bulgy eyes sprouting antennae and six gangly legs, a praying mantid may frighten and fascinate. We're finding a lot of young, green mantids in city and suburban gardens. These nymphs won't hurt us, but small insects such as fruit flies and crickets had better beware. Mantids are opportunistic eaters, capturing and devouring live prey (including other mantids) within leg's reach.

They're slow to hide, though, giving us time to marvel at their odd, alien-looking form. A coworker recently found one that posed quite cooperatively for several pictures before it got restless enough to hop off her hand.

Young mantids emerge from their egg cases from early spring to midsummer, explained Casey Sclar, entomologist in Longwood Garden's Plant Health Care Division. In Pennsylvania, they'll likely be either Chinese or European mantids, which have displaced the much smaller native mantid. There are nearly 2,000 mantid species worldwide.

The Chinese mantid is large (adults reach more than 4 inches) and brown with green or yellow stripes along the sides of the wings. The European mantid, also green or brown, reaches about 3 inches at maturity. This one is distinguished by a bull's- eye under its foreleg.

Should we encourage carnivorous mantids that eat so indiscriminately, even selective beneficial insects? "Conserve and appreciate mantids," urged Sclar. "They are natural enemies of garden pests. They eat other chewing insects like caterpillars." Although he noted that they are not as good a choice for biocontrol as green lacewings, which consume large quantities of a wide variety of small insects including aphids, whiteflies, thrips, mealybugs, mites, small caterpillars, leafhoppers, and moths.

Mantid egg cases contain hundreds of eggs, so leave them in the garden or put them on a nearby infested plant, Sclar suggested. Many a naive nature lover has brought an egg case indoors. The story's the same: surprise, then annoyance when hoards of young hatch and swarm throughout the house.

Ambush Predators
With their inconspicuous green and/or gray coloring and leaf-like shape, mantids are well camouflaged amidst foliage, stems, and twigs. A mantid's head can rotate 180 degrees while it sits and waits for insects like moths, butterflies, and caterpillars to fly or crawl nearby. In the hunting (or praying) position, the mantid's two front legs fold under its head. Those front legs strike out and capture prey. Long sharp spines along the legs hold the prey while the mantid devours it.

Unfriendly Mating Behavior
Mantid reproduction is no nonsense. The smaller male mounts the female, who's likely to bite off his head during the process. Sclar confirmed that being headless increases the male's "output." One theory is that the male's fluid provides protein for egg production.

Does the female eat the male after mating? Experts disagree. Research in 1984 found that this happened less frequently than previously thought. Why would she do this at all? Survival of the species. The theory here is that eating her mate provides food for the female, sustaining her to carry eggs with the male's genes.

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