by Whit Gibbons

July 23, 2017

To paraphrase the journalistic aphorism: Bird eats insect is not news; insect eats bird is. And that news has been confirmed by Martin Nyffeler of the University of Basel in Switzerland with his colleagues Michael R. Maxwell of National University, La Jolla, Calif., and J. V. Remsen of LSU.

The researchers have recently uncovered many examples of these predator-prey surprises. This edifying scientific paper is one of those that can change our perception of the way the natural world works.

Small birds are the prey. Large praying mantises are the predators. The scientists accumulated records of these voracious ambush hunters attacking birds in a variety of situations on every continent except Antarctica.

The absence of praying mantises at the South Pole and the large size of penguins makes a forthcoming report unlikely. Nonetheless, in warm regions of the world where these carnivorous insects live, numerous accounts exist of mantises eating birds.

Praying mantises look like something you might find at a Star Wars battle. Their huge eyes framing a triangular head give them a decidedly alien appearance. The front legs are held in an upright position with spines on the inside of what would be functionally equivalent to a claw and a long wrist that folds toward the forearm, also with spines.

When the two parts of the leg are pulled toward each other, the prey is held tightly in a thorny vice grip. Praying mantises are so effective at holding on to prey that, when humans did not intervene, about 98 percent of the captured birds were eaten by the mantis. As if this were not enough of a horror scene, a mantis first attacks the bird’s head and then eats the brain of the victim.

The researchers documented the capture of two dozen different species of small birds from 13 countries by a dozen kinds of mantises. More than a hundred of the records were from the United States, and the ruby-throated hummingbird was the most common victim. Considering the size differential between most insects and most birds, the favored bird prey by a praying mantis is not surprising.

The odds in favor of the mantis are further increased when the crafty mantis learns that the underside of a hummingbird feeder is an ideal spot for an ambush predator to hang out. Some bird enthusiasts will be pleased to know that records also exist of avian species turning the tables by eating mantises. Crows, owls and kingfishers have been reported to eat praying mantises in other countries and would presumably do so here. But again, bird eats insect is not news. Insect eats bird is.

The most common praying mantis native to North America is the Carolina mantis, so-called because the first specimen was described in South Carolina in the 1700s. They are typically green, which serves them well when camouflaged in vegetation, or brown. Carolina mantises get as long as 2½ inches and are widespread across the Southeast. As with many kinds of native plants and animals, Carolina mantises are sometimes overshadowed by introduced species from other continents.

Both Chinese and European praying mantises are larger than our native species. The Chinese mantis can be more than 4 inches long. The introduced praying mantises were first reported in the United States in the 1890s from what is presumed to be accidental introductions, probably by eggs attached to horticultural plants.

These days, some garden outlets actually sell eggs of praying mantises for people to put in their gardens to control insect pests. The researchers end their article with a warning: “The predation risk that [praying mantises] pose to some bird species, particularly hummingbirds, lead us to recommend caution in [their release] into North American gardens.”

One thing is for certain, we can all take comfort in the fact that praying mantises do not grow large enough to pose a threat to humans. Otherwise, living in Antarctica might become appealing.

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