The European mantis (Mantis religiosa) is a large hemimetabolic insect in the family of the Mantidae ('mantids'), which is the largest family of the order Mantodea (mantises). Their common name praying mantis is derived from the distinctive posture of the first pair of legs that can be observed in animals in repose. It resembles a praying attitude. Both males and females have elongated bodies with two pairs of wings. The most striking features that all Mantodea share are a very mobile, triangular head with large compound eyes and their first pair of legs (the 'raptorial legs'), which is highly modified for the efficient capture and restraint of fast-moving or flying prey.
In Germany, M. religiosa is listed as Gefährdet [endangered] on the German Red List on the basis of an assessment from 1998. It is not supposed to be caught or held as a pet. At a global level, it is assessed by the IUCN as least concern.
The phenomenon that conspecifics are attacked and eaten after, during, and even before copulation is called sexual cannibalism. Many examples are known in various groups of invertebrates, including the mantids. Some speculations exist about the benefits of this behaviour, but its causes are not fully understood yet. For quite some time, the belief that sexual cannibalism in M. religiosa only occurred in captivity was widespread. It was believed to be an artefact of improper animal keeping (too little food or space). In 1992, however, the cannibalising behaviour of female M. religiosa was observed in a field study. Lawrence compared the percentage of cannibalism in natural and manipulated (males and females were put close together in the field) pairings and found rates of 31% and 24%. This proves that sexual cannibalism in this praying mantid is not caused by laboratory conditions. They can, however, intensify the phenomenon; females that were starved for more than three days were more likely to attack males, even before copulation. While the cannibalisation before the copulation is still puzzling to scientists, some theories about the benefits of sexual cannibalism in general include:
Eating her mate provides the female with nutrients so she does not have to hunt. She has a prey item available that is bigger than the prey she would be able to catch in the manner she usually hunts.
The meal also usually takes place during or shortly after she was fertilised, giving her more resources for the faster production of a large ootheca with large eggs, thus increasing the chance of her offspring to survive. Males have also been known to be more attracted to heavier, well-nourished females for this reason.
At first glance, however, this behaviour does not seem to be very beneficial for the male, since he dies and cannot create more offspring with his genetic material, yet males usually do not mate more than once, anyway. They have a shorter life expectancy than females (7–8 months versus 11–12 months) and since food can begin to become scarce in September and October, the male might starve before he has the chance to mate again. Copulation is also known to take longer when cannibalisation occurs. It seems advantageous to transfer more sperm in this elongated time and additionally provide the female with nutrients. Doing this, the male might just pass on his genes once, but he can ‘make sure’ that his offspring are successful, since they come from a well-nourished female.
Some controversy exists, though, concerning this theory. The absence of elaborate display behaviour does not support this ‘selfless’ behaviour of the males. It could have also been observed that males are more likely to approach a female that is distracted by feeding or cleaning herself. The approach is also happening faster in these cases. The male seems to try to avoid his cannibalisation very actively.
The fact that sexual cannibalisation happens so often is surely also supported because a male without a head can continue and even initiate copulation. The cerebral ganglion might have an inhibitory effect on copulatory reflexes. Once it is removed by removing the head, copulation might even be longer, since the male can never ‘decide’ to let go. A few mantids can also start copulating when the heads of both animals get removed artificially beforehand. The beheaded animals can live up to five hours and usually just die when they bleed out or starve to death.
