Praying mantids used to be lumped with grasshoppers in the order Orthoptera. They were taken out of there and became a suborder in the Dictyoptera along with the stick insects and the cockroaches, but most experts prefer to put them in their own Order, Mantodea. Mantids are large carnivorous insects with long, raptorial front legs which are held in front of them as if they were praying but what they are really doing is preying. They wait for possible food species to come in reach and then snap those legs out to catch the unfortunate insect in a spiny and deadly grasp. There are about 2000 described species of mantids and most live in the warmer parts of the world, especially the tropics and subtropics.
My textbook (CSIRO Insects of Australia, p 294) describes the Order this way: “Mandibulate, predacious, exopterygote Neoptera, having raptorial fore legs with large mobile coxae; pronotum without large, descending lateral lobes; wing rudiments of nymph not reversing their orientation in the later instars; specialized auditory and saltatorial organs lacking. Eggs enclosed in an ootheca.” In English, this means that they have mandibles, are predators, have an incomplete life cycle, are winged and have large forelegs with the first segment (the coxa) large and moveable. The pronotum is just behind the neck and a different shape than the Orthoptera or grasshoppers, and this is one of the reasons the Mantids were removed from that order. Mantids also do not have specialised jumping legs like the grasshoppers, nor do they have the auditory organs on their legs, which grasshoppers used to ‘stridulate’. Also, in Orthopterans, the young nymph stages have wing rudiments that are reversed in orientation to the adult form, but this is not the case in mantids. Mantid eggs are encased in an egg case, called an ootheca, which is attached to twigs and looks a bit like a brown plant growth.
Sexes are separate in the mantids. Males often have larger ocelli (3 simple eyes between the compound eyes) than the females and in Australian mantids, the males have fully functional wings while the female’s wings are reduced or absent. The females exude a foamy ootheca or egg case in the twigs or branches of vegetation and fill it with thin-shelled, round eggs. The ootheca then hardens and protects the eggs. There are dorsal holes in the ootheca for the hatchlings to use to escape, usually in the spring. The nymphs are tiny replicas of their parents, but having only rudimentary wings and short antennae. They have to moult several times, with the wing rudiments and antennae increasing in length each time.
Adult mantids lead solitary lives, A few species live on the ground but most sit in shrubs and on tree trunks. Much of their time is spent in the praying position, sometimes absolutely still or sometimes swaying gently, much like stick insects. They have large eyes for spotting prey and can turn their heads 180 degrees to help them in this. Many species are cryptically coloured and shaped to help them blend into their backgrounds for both protection and so that they are not seen by their prey. If disturbed or threatened they can run, jump or, in some cases, fly away. Some have brightly colored wings and may flare these out when threatened to make themselves look bigger and more aggressive. They can strike out with their spiny forelegs too.
Mantids are strictly carnivorous, catching and eating insects and spiders and even other, smaller mantids with their fore legs. I once raised some mantids in a small terrarium, feeding them on flies. One young female decided flies weren’t good enough and before I knew it, she had consumed her brothers and sisters. She was a very aware insect. She could see me coming and would look at me to see if I had something juicy for her to eat. Many mantid females also attack and eat their mates and the males are programmed to keep on mounting, clasping and thrusting in the spermatophores even after their head has been removed by their partner. This is a rather gruesome end to the mating game, but the female then recycles her mate into the next generation so there is survival value in this cannibalistic behavior.
Mantids are also subject to predation by other animals, especially birds, lizards and insectivorous mammals. The eggs and small nymphs are preyed upong by crickets and a number of parasitoid wasps lay their eggs in Mantid eggs. These hatch and eat the nymphs from the inside out. Consequently mantid numbers are usually low.
Mantids are one of the better insects to keep as pets because they are easy to keep and feed and because they are or seem to be more intelligent than the average cockroach. However it is best to keep them alone if you don’t want them to eat each other.
References; CSIRO. 1979. The Insects of Australia. Melbourne University Press. http://www.ento.csiro.au/education/insects/mantodea.html http://www.ca.uky.edu/entomology/entfacts/ef418.asp