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(515) 294-9915
10/9/00
Contacts:
Donald Lewis, Extension Entomology, (515) 294-1101,
drlewis@iastate.edu
Elaine Edwards, Extension Communication Systems, (515)
294-5168, eedwards@iastate.edu
Yard and Garden Column for the Week Beginning Oct. 13
Now Let Us Prey
By Donald R. Lewis
Extension Entomologist
Iowa State University Extension
I've often thought that the praying mantis looks like an insect that was put together by a committee. Their peculiar appearance, however, certainly makes them easy to recognize. They have a long narrow body that is especially stretched in the middle where the legs attach. They have a puny triangular head with two large compound eyes. But most of all, they have those impressive, oversized front legs held upright in front of the face.
There are more than 1,500 different kinds of mantids (preferred plural form of mantis) in the world. Most of these are tropical insects, and only about 20 kinds occur in the United States. Unfortunately, only 5 species are common.
Praying mantids have never been numerous in Iowa and historically they were only common in the far southeastern corner of the state. Beginning a few years ago more mantids were reported further north and west in Iowa and this summer they were noticeably abundant as far north as Ames and as far west as Council Bluffs. The easy conjecture is that the northward spread was facilitated by consecutive winters with mild weather. This theory is logical but unproven.
The two kinds of mantids likely to be seen in Iowa are the Chinese mantis and the Carolina mantis. Both are large, long, slender and slow. The larger, Chinese mantis may have a body length (without front legs) of 3 to 4.25 inches. The Carolina mantis is 1.75 to 2.5 inches in length. The body is tannish-brown or green with the narrow front wings marked with a green line along the front edge.
The front legs are by far the most distinguishing feature. They are highly modified for capturing prey and are not used for walking. They are held upright in front of the head and hinge in the middle to open and close like a pocket knife blade against its handle. Along the inside of the leg sections are alternating rows of long and short spines that tightly and convincingly impale any insect unlucky enough to get into the mantid's grasp.
Efficient hunters
Praying mantids feed only on living prey such as moths, crickets, grasshoppers and flies. Their success starts with a "lie-and-wait" approach to hunting made possible by effective camouflage coloration. The large compound eyes at the top of the small, flexible head provide excellent stereoscopic vision. The freely movable head can twist almost clear around allowing the mantis to look over its own shoulders.
Any movement by a potential prey is readily spotted and briefly studied. If the prey is too far away, the mantid may close in at a very slow crawl until within striking distance. If the creature is too close, the mantid may attempt to push it away.
What happens next is an amazing display of speed and precision. The folded upraised front legs extend and snap open, grasp the insect and snap shut in a high-speed blur. Once caught, the victim is a goner. Almost no one escapes the mantid's deadly grasp and the quick, immobilizing bites that follow. According to some estimates a striking mantis is successful at capturing its prey 85 percent of the time. And they get lots of practice. A healthy and hungry mantid can consume up to 15 crickets a day.
Mantid meal time is not a pretty sight (though morbidly fascinating to some). Captured prey are securely clutched and transported still alive to the mandibles. These small but strong pincers quickly chop even large prey to bite-sized fragments suitable for swallowing. Greedy mantids can sometimes grab a second prey while still munching on the first one. We call these insects "praying" mantids because of the pious, prayerful position of the upright front legs. The cold-blooded feeding habits might make "preying" mantid a more accurate term.
What about mates as meals? A common misconception is that female mantids always eat their partners during or after mating. This behavior, aptly named sexual cannibalism, does not occur in all species or in all matings. In fact, in only one species, the European mantid, is this behavior noted and then only infrequently and while being closely observed in artificial or captive conditions.
Garden Good Guys?
Mantids are beneficial because they consume other insects. However, their impact in the garden and landscape is probably negligible. True, they do prey on pests, but they will eat virtually anything they can catch. They do not discriminate between beneficial and harmful garden insects and will eat their siblings, other beneficial insects, butterflies and pollinators such as bees. Mantids may not provide much pest relief in your garden but they are an incredible source of amazement. Enjoy.
ml: isugarden
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