Human society is male dominant, but in the case of mantises or spiders it is the reverse. The female mantises are many times larger than the male. When the time comes to mate, the male mantis approaches the female carefully. He flaps his wings, sways his abdomen and makes a few circles around the female. Then copulation begins. Leaping on her back, he begins to mate. But this is often the male’s last act. While the male is busy making love to its partner, the female tears off her unwary male’s head. The female mantis eats the head of the still-mating male and then moves on to the rest of his body.
Mantises are formidable predators. They have triangular heads poised on long necks (elongated thorax). Typically green or brown and well camouflaged amongst the greenery in which they live, mantises lie in ambush or patiently stalk their quarry. They use their front legs to snare their prey with reflexes so quick that they are not visible to the naked eye. Their legs are further equipped with spikes for snaring prey and pinning them down.
The Praying Mantises got their name on account of their prominent front legs, which are bent and held together at an angle that suggests the position of prayer. But though they seem cultured and in prayer, the females are by no means virtuous. “If you put a pair together and come back later, you’ll just find the wings of the male and no other evidence he was ever there,” say researchers who investigated this interesting phenomena recognized as sexual cannibalism. Sexual cannibalism has fascinated biologists ever since Darwin. It is not limited to mantises, but is also found in other invertebrates, including spiders, midges and perhaps horned nudibranchs.
Honeymoon widows
This is also the sad fate of male Black Widow spiders. Black widows are notorious spiders identified by the coloured, hourglass-shaped mark on their abdomens and in fact they get their name from their habit of killing the male on first mating, leaving the female a ‘widow’. Female black widows mostly feed on their male partners after mating. The females are bigger than the males and also contain more venom, which is at least three times more potent than that of the males’, research reveals. Thus, even if a male bites the female in self-defence, on being bitten by the female, he would succumb to his death more rapidly and is therefore more likely to be eaten.
In fact the spider’s bite is much feared because its venom is reported to be 15 times stronger than a rattlesnake’s. If a human is bitten, he/she will expereince muscle aches, nausea, and a paralysis of the diaphragm that can make breathing difficult. However, contrary to popular belief, most people who are bitten suffer no serious damage, let alone death. But bites can be fatal to small children, the elderly, or the infirm. Fortunately, fatalities are fairly rare; the spiders are non aggressive and bite only in self-defence, such as when someone accidentally sits on them. So the male black widow doesn’t stand a chance at all, if a female bites it. To feed, black widows puncture their insect prey with their fangs and administer digestive enzymes to the corpses. By using these enzymes and their gnashing fangs, the spiders liquefy their prey’s bodies and suck up the resulting fluid. These spiders spin large webs in which females suspend a cocoon with hundreds of eggs. The spiderlings disperse soon after they leave their eggs, but the web remains. Black widow spiders also use their webs to ensnare their prey, which are mostly flies, mosquitoes, grasshoppers, beetles and caterpillars. Black widows are comb-footed spiders, which mean they have bristles on their hind legs that they use to cover their prey with silk, once it is trapped. You will be relieved to know black widow spiders are found only in America and Australia.
Some other species of spiders such as the red-backed spider too shows this sexual cannibalism and also the horned nudibranch which is a mollusc which lives on the sea floor. Human scientists who are from male dominant societies still debate on why this kind of strange behaviour evolved in these species. There are several theories and most scientists believe that the voracious appetite of the hungry females lead to the cannibalism. The males are vulnerable at the time of mating and the hungry females don’t waste a chance to change their honeymoon beds to dinner tables. But experiments have also suggested that it is a strategy that females use to select the best fathers for their offspring.
Monogamy to the extreme
In some cases, sexual cannibalism may characterize an extreme form of male monogamous behaviour, in which the male will sacrifice itself to the female. Males may gain reproductive success from being cannibalized by either providing nutrients to the female (indirectly to the offspring), or through enhancing the probability that their sperm will be used to fertilize the female’s eggs.
Some zoologists also propose the theory that males too played a role in the evolution of sexual cannibalism by surrendering themselves to the female. They believe this act of submissiveness increases male reproductive success, as their bodies nourish the mothers of their offspring, raising the odds that those offspring would successfully hatch and grow up to produce their own offspring, thus carrying on the father’s genes. Research has also revealed that cannibalized males father twice as many offspring with a female that mates with other males. In this perspective, it can be considered as the ultimate fatherly sacrifice.
Scientists also say that cannibalism provides the males, extra time to put a plug in a female’s sperm receptacle. Researchers have also made an interesting observation of the orb-weaving spiders where the males suddenly die, as they mate - the male’s death may be a strategy for preventing other males from mating with the female as in death, its sexual organ becomes stuck in the female’s receptacle. Even if she feeds on the rest of his body, the organ remains, preventing further breeding.
It is believed different species could have different reasons for preying on the mating male. Scientific research reveals that all of the above reasons could be true. Whatever the reasons, these male mantises and spiders sacrifice themselves on their honeymoon night. So if human society can dedicate a day to the cause of betterment of the female, then perhaps the males of the mantises and spiders should form a few NGOs, protesting to initiate a day dedicated for males in their society. Don’t you think?
Insects in the Zoological Gardens
Insects conquered the earth before humans, and still are one of the largest groups of animals on earth. There are many interesting insects and many of the modern zoos have a separate section to showcase this amazing world of insects. These insect zoos are in addition to butterfly gardens that are an attraction in many zoological gardens. The insect section of the Malaysia zoo set up recently is a refuge for over 200 species. Mantises, stick insects, tarantula, scorpions, Madagascar’s hissing cockroaches are some of the insects that are the usual attractions and are kept in these insect zoos.
Dehiwala Zoo has a butterfly garden which is still under repair and this also used to have a few leaf insects and stick insects other than butterflies, in its glory days. Let’s hope once the repairs are finished, we will once again get a chance to observe interesting butterflies and other insect
Published on LakbimaNews on 18.03.2011
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