Praying mantises able to feed on hummingbirds, other avians
Tom Vaughan, a photographer then living in Colorado’s Mancos Valley, kept a hummingbird feeder outside his house. One morning, he stepped through the portico door and noticed a black-chinned hummingbird dangling from the side of the red plastic feeder like a stray Christmas ornament.
At first, Vaughan thought he knew what was going on. “I’d previously seen a hummingbird in a state of torpor,” he said, “when it was hanging straight down by its feet, regenerating its batteries, before dropping down and flying off.”
On closer inspection, Vaughan saw that the hummingbird was hanging not by its feet but by its head. And forget about jumping its batteries: The bird was in the grip of a 3-inch-long green praying mantis.
The mantis was clinging with its back legs to the rim of the feeder, holding its feathered catch in its powerful, seemingly reverent front legs, and methodically chewing through the hummingbird’s skull to get at the nutritious brain tissue within.
“Talk about cognitive dissonance,” Vaughan said. “I always thought of mantises as wonderful things to have in your garden to get rid of bugs, but it turns out they sometimes go for larger prey, too.
“It gave me new respect for mantises,” he added.
Vaughan’s sentiment is echoed by a cadre of researchers who place mantises in a class of their own among the swarming class
and the researchers are discovering a range of skills and predilections that make mantises act like aspiring vertebrates.
Praying mantises are the only insects able to swivel their heads and stare at you. Those piercing eyes are much like yours, equipped with 3-D vision and a fovea — a centralized concentration of light receptors — the better to focus and track.
A mantis can jump as unerringly as a cat, controlling its trajectory through an intricate series of twists and turns distributed across its legs and body, all to ensure a flawless landing on a ridiculously iffy target nearly every time.
The mantis appetite likewise turns out to leap and bound, with scant regard for food-chain decorum.
By the standard alimentary sequence, insects feed
on plants or one another, and then birds hunt down insects. But just as there are carnivorous plants such as the Venus flytrap, mantises prey on hummingbirds and other small-to-middling birds more often than most people realize.
James V. Remsen of the Museum of Natural Science at Louisiana State University and his colleagues documented 147 cases of mantis-on-bird predation in 13 countries representing all continents but Antarctica — not surprising, Remsen said in an interview, because there are no mantises on Antarctica.
Hummingbirds were the most common target, but mantises also went after warblers, sunbirds, honeyeaters, flycatchers, vireos and European robins. Large species such as the Chinese mantis, which grows to 4 inches in length, were the most-avid avivores, and females were responsible for virtually all the bird killing observed worldwide.
In two reported cases, females feasted on birds while copulating with males. Sometimes the mantises would tuck in through the bird’s breastbone, but more often they went for the head, Remsen said.
Hunting is a professional trademark of the mantid order: The 2,500 known species are all predators, usually of insects and other small invertebrates. Some mantises chase down their prey, but many are consummate ambush artists, waiting with Zen stillness in the grass or among flowers for the right moment to strike.
The female mantis has a bottomless appetite, perhaps driven by the extraordinary size of her egg case, or ootheca, a frothy proteinous mass studded with up to 400 eggs that can amount to half her body weight.
The female secretes the bulging capsule onto a twig or other surface, where it hardens and protects the eggs as they develop. The job is so energy-intensive she can rarely manage an encore.
The difficulty of securing enough calories to fabricate an ootheca may help explain why females of some mantid species famously engage in sexual cannibalism — consuming their mates after, or even during, copulation. Whether a male mantis sacrifices himself for the sake of his progeny or merely fails to dart away from the female in time remains a topic of active research.
The mantises’ closest relatives are the cockroaches, from which they diverged about 250 million years ago, said Gavin J. Svenson, curator of invertebrate zoology at the Cleveland Museum of Natural History and a leading authority on praying mantises. The family resemblance can still be seen in the long, slender antennae and the triangular, movie-alien shape of the head, among other features.
But praying mantises rise above the flattened scuttling posture that makes cockroaches look so ... verminy. Praying mantises “are unusually charismatic,” said William D. Brown, who studies them at the State University of New York at Fredonia. Those large eyes, the way they turn to look at you, gives them a “certain personality” that most insects lack, he added.
Those eyes detect prey. Mantises’ exceptionally sophisticated eyesight has lately caught the attention of researchers. By seeing in stereo — that is, mentally triangulating the slightly different images received from two eyes into a single line of sight — an animal can get a sense of depth and distance.
“It’s a complex ability, and we’re still trying to understand the algorithms, the calculations, that our own brains use to do it,” said Jenny Read of the Institute of Neuroscience at Newcastle University in Britain, who with colleagues recently demonstrated that praying mantises have stereoptic, or 3-D, vision.
“Our brain is five orders of magnitude bigger than theirs,” Read said. “So either our visual cortex is doing incredibly impressive things I don’t know about yet, or we could get rid of most of it and replace it with a praying mantis brain.”