Looks like a praying mantis, hunts like a praying mantis, but is not a praying mantis. Meet the green mantisfly.
Generally speaking, when we think of raptors we think of birds of prey like hawks or falcons or, if you are not a purist, maybe even non-feathered reptiles like velociraptors, made famous in Jurassic Park. Actually, raptor comes from the Latin word rapere, which means "to seize or take by force.” The term raptorial pops up in the entomological lexicon when we talk about the highly modified forelegs of some predatory insects. Their frontmost pair of legs has been shaped by millions of years of evolution for the express purpose of capturing and holding prey. They have evolved in at least four orders of insects, including the Mantodea (mantises), Neuroptera (mantisflies), Diptera (dance flies and others), and Hemiptera (ambush bugs and others).
This small mantisfly stopped by for a short photoshoot. Notice its spiny forelegs designed by nature to snare unsuspecting prey. After glamming for the camera, it flicked me off and said “see ya’ later.” Placed on a milkweed in my garden, it groomed for a few moments, bowed twice, and took flight. Though similar in appearance, mantisflies are not close relatives of praying mantises.
Although less than an inch in length, this tiny mantis is equipped with raptorial forelegs armed with sharp spines on femur and tibia to snare unsuspecting prey.
Last week while bumbling around the wilds of the Potomac we had the good fortune of encountering two of these clever predators, a pretty green mantisfly adult, Zeugomantispa minuta, and a tiny juvenile praying mantis, likely the Chinese mantis, Tenodera sinensis. Raptorial forelegs of both mantisflies and mantises are endowed with sharp spines perfect for snaring prey. The joint where femur and tibia meet is a hinge. Strong internal muscles contract and draw the femur and tibia together, allowing deadly spines to grasp the hapless victim, preventing its escape. At less than an inch in length, the adult green mantisfly is tiny. It is dwarfed by its near namesake the praying mantis, which in the case of the Chinese mantis can be almost five times larger. As adults, both the mantisfly and mantis are sit-and-wait predators which ambush and capture a wide variety of unsuspecting insects that venture too near these motionless and cryptically colored predators. Mantisflies are also reported to actively hunt their prey. Not surprisingly, the green mantisfly takes small soft-bodied prey, including aphids. However, large mantises like the Chinese mantis eat small reptiles, amphibians, and hummingbirds in addition to insects. So, don’t place that hummingbird feeder near a plant or structure where a hungry mantis may be lurking. And yes, females do practice sexual cannibalism and sometimes consume their mates. Courtship in mantises is a risky proposition for the guys. Watch out boy, she’ll chew you up. She’s a man eater!
Legs are used for stalking and catching prey, and grooming legs appears to be important business even for small praying mantises. Watch as this youngster slowly stalks a fly. As the fly (upper left corner) comes into range, the mantis makes a lightning-fast strike. Did raptorial legs of the mantis hit the mark? You bet. Resting on a lower leaf, the mantis enjoys a well-earned meal held snugly by its spiny forelegs.
While adults of both of these insects share similar dining styles, juvenile stages differ dramatically in their behaviors and cuisine. Juvenile mantises, called nymphs, are also sit-and-wait predators like the adults and feast on many small invertebrates as meals. Juvenile mantisflies are predators or parasitoids of other arthropods, including several kinds of insects such as larval stages of beetles, moths, butterflies, bees, ants, wasps, flies, termites, and spiders. Our friend the green mantisfly is in the subfamily Mantispinae. Larvae in this group are only known to feed on spider eggs within egg sacs of spiders. Tiny hatchling larvae may either seek out and directly penetrate a spider egg sac, or they may hang out on a leaf, hitch a ride with a passing female spider, and when she constructs an egg sac they will hop off and enter the egg sac. Once inside the egg sac, larvae dine on nutrient rich spider eggs before completing their development and pupating.
Despite their similar appearance and mode of capturing prey, praying mantises and mantisflies are not closely related to each other. Striking similarities of their remarkable raptorial legs are a fascinating example of evolution shaping morphological structure to the similar function of capturing prey in two very different predators.
Acknowledgements
Bug of the Week thanks Eloise for discovering the tiny praying mantis that served as the inspiration for this episode. Dr. Shrewsbury provided insights into feeding behaviors of larval mantisflies. “Functional morphology of the raptorial forelegs in Mantispa styriaca (Insecta: Neuroptera)” by Sebastian Büsse, Fabian Bäumler & Stanislav N. Gorb, and “Vision in the mantispid: a sit-and-wait and stalking predatory insect” by Karl Kral, were consulted as references for this story.