On most nights I like to turn the porch light on, just to see what insects are flying in the neighborhood. Last night I stepped outside to check the light, and was instantly hit by a huge insect that bounced off my head and landed on the ground. To my surprise and delight it turned out to be a giant praying mantis. And not just any praying mantis – this was the largest praying mantis to be found in our neck of the woods, and it was also the second species of these remarkable insects to visit my garden this year.
All my life I have been dreaming of living in a place where winters are mild and mantids are plentiful. Although I cannot say that I have completely fulfilled my dream (winters in Boston are two orders of magnitude worse than in my native Poland), praying mantids are quite common. Two species are found in New England: the European mantis (Mantis religiosa) and the Chinese mantis (Tenodera parasinensis)*, and both were introduced to North America from other places over a century ago. To find native praying mantids in the US you would need to go South to at least New Jersey.
Of the two species found in New England, the Chinese mantis is significantly larger, but more slender. Both species come in a variety of colors that range from dark brown to light green, but you can easily tell them apart by two, easy to see differences: the European mantis has a black and white spot between its front legs, whereas the Chinese mantis has dark hind wings (another introduced species similar to the Chinese mantis, Tenodera angustifolia, has clear hind wings, but with a similarly darkened front edge.) Although the European and Chinese mantids are not very closely related – they belong to two different tribes of the family Mantidae – they appear to be attracted to each other, and I have seen individuals of these two different species mating (although such an affair is very unlikely to produce viable offspring.) Speaking of which, females in these two species do occasionally eat their partners during, or shortly after, mating. And yet, somewhat creepily, the abdomen of a half-eaten male continues to copulate with the female. The evolutionary advantage of this behavior is clear – by sacrificing his body, the male directly contributes to the survival of his offspring by feeding the female, and making her more likely to lay a large, healthy clutch of eggs.
The European mantis first appeared in the United States in the late 19th century, most likely introduced inadvertently with nursery plants. Since then it has spread to all states (except Alaska, of course), not in small part because it is being sold as a pest-control agent by many garden supply companies. Alas, praying mantids do not make very good pest-control animals, as they will first go after each other, before starting to eat pests in your garden. The Chinese mantis was apparently introduced on purpose in 1896 (although I have not been able to track down a reliable source of this information), to help control agricultural pests.
The impact of these two introduced species on the local insect fauna is difficult to judge. Unlike many other non-native species, praying mantids in New England are not competing directly with any indigenous species. They are generalists in their diet, and they themselves are likely to provide large, nutritious meals to native birds and mammals. The story is probably different further down South and in the western United States, where the introduced species compete directly with native mantids.
Still, I cannot suppress a smile when I see one of these gorgeous creatures, and now that I know that two species of these insects visit my garden, I feel that I can cope with harsh New England winters a little better.
Update (10:23 pm, Sept. 14th, 2012): Kristin has just found another Chinese mantis on our deck!
*)The Chinese mantis is usually referred to as Tenodera sinensis or Tenodera aridifolia sinensis. However, these names are, technically speaking, junior homonyms, and the scientific name of this species was changed by Daniel Otte in 2004 to Tenodera parasinensis.