Praying Mantis

The praying mantis refers to a group of insects comprising about 2,400 species around the world.  Most of these animals live in rainforests, but there are eighteen species that live in North America.  The Carolina mantis, Stagmomantis carolina, is the only species native to Illinois and can be found in the southern half of the state.  The most common mantis found in northern Illinois, as well as throughout the U.S., is the Chinese mantis, Tenodera sinensis, originally introduced in the Philadelphia area in the early 1900s to control agricultural pests.

Praying mantises are the only insects that have a unique, flexible joint located between the head and prothorax allowing their heads to turn a full 180 degrees to look straight backwards.  Mantis species have two large compound eyes composed of dozens of ommatidia.  Humans have a simple eye, one ommatidium, that creates 3-dimensional images by comparing light and dark patterns to discern depth.  A mantis detects movement from the many angles of each ommatidium and forms a 3-d image showing direction and distance.  Mantises have only one ear, located on the belly just in front of the hind legs.  They can hear a full range of sound including ultrasounds, but cannot detect frequencies or direction.  Ultrasound detection allows a mantis in flight to avoid potential predators, such as bats, that use ultrasound echolocation to identify prey.

Many animals, especially in tropical rainforests, use heavy vegetation for cover.  The praying mantis is an ambush hunter, stalking prey with slow, stealthy movements or waiting for prey to come close before pouncing and using the sharp spines on its forelegs to grab and hold the prey.  Most mantises are camouflaged with colors and patterns that easily blend in with their native habitat.  Here in Illinois, they are plain, dull colors of green, gray or brown.  The Chinese mantis is one of the best hunters of any mantis species, and it is adept at capturing birds.  In the U.S., their favorite prey is the Ruby-throated hummingbird. 

In late summer, praying mantis males and females mate and females will lay eggs a few weeks later.  Males try to mate with as many females as they can.  However, there is danger for the males during this activity.  Females are larger and may cannibalize the males during mating.  This only happens about 20% of the time, and females gain important amino acids that end up in the eggs and allow the females to produce more eggs than she otherwise would.  In late autumn, females deposit 50 to 200 individual eggs  along a twig or stem, attaching each egg by covering it with a frothy, foam-like substance, that hardens  creating an egg case called an ootheca.  The eggs will remain encased until spring.  The average life span is about a year; adults in the tropics live slightly longer, but adults in temperate zones will die over winter.

Praying mantises eat lots of insects, and they have been imported into many areas to provide pest control for agriculture.  This has not worked very well because mantises are generalists when it comes to prey, eating everything without distinguishing between “good” garden bugs and “bad” garden bugs.  Having several in your garden may result in removing just as many pollinator species as pest species.  Praying mantis can grow up to five inches, but carry no toxins, venom, stingers, or infectious diseases  and are harmless  to humans.  Be on the lookout for the egg cases among the bare branches in your yard this winter and be prepared to observe them hatch in the spring and populate your yard.