Written by Joe Ballenger
Mantises, as we’ve seen, are interesting animals with a lot more going on than what it seems. They’re efficient predators which have an evolutionary history that many wouldn’t suspect, and they have their own weird biological quirks.
One habit in particular which interests people is the fact that these animals are very antagonistic towards one another. If you put more than one mantis in a container, someone’s going to get eaten before too long.
Sometimes, this happens with hatchlings. Right out of the ootheca, mantids are ready to go and have no qualms about eating siblings. Other times this happens during mating, with the female eating the male during the process.
Since we’re dedicating an entire month to mantids, it goes without saying that we should say something about sexual cannibalism as it relates to mantids because there’s a lot of mythology surrounding their mating habits. Their mating habits are also interesting to me because they defy a lot of assumptions which people have about animal mating habits.
The National Geographic video below discusses the standard way people think about mantis mating. Unfortunately, the video isn’t quite accurate. Mantis cannibalism isn’t very common, and what actually happens is a lot more complicated than the video lets on.
The study of sex in animals is interesting because it’s full of stereotypes humans imbue onto the animals they study. A lot of the myths that occur in the animal world are largely the result of humans trying to frame the behavior of the animal into a human-centric mindset which is heavily influenced by perceptions shaped more by culture than reality.
One example of such a bias is Bateman’s rule, which assumes females to be choosy while assuming males will mate with essentially any female they have access to. It’s a very flawed idea, but many people still believe that animals act this way despite the fact that almost no animals-including humans-actually act this way. We’ll get back to this idea at the end of the article, but I wanted to introduce it at the beginning so it would be in the back of your mind as you read on.
Does sexual cannibalism exist in mantids?
Sexual cannibalism exists in mantids, but it’s completely unlike what’s described in the video above. Many people believe that sexual cannibalism is common, or even required, in mantids. This, however, is not the case.
There is no species which requires cannibalism in order to mate, and cannibalism only happens about 30 percent of the time depending on various factors including species, season and food availability. When the males are eaten, they’re usually eaten before mating takes place. Although it’s not the obligate cannibalism implied by the video, approaching a female still results in a significant risk to the male. Cannibalism in mantids has also been thought to change the ratio of males to females in wild populations.
Instead of being an integral part of the mating process, cannibalism occurs when the females are hungry. In reality, cannibalism is tied more into how hungry the female is rather than the male’s willingness to sacrifice himself. Females who eat males do produce more eggs, but it’s unclear whether male mantids are better when compared to other food sources. Some authors have even hypothesized that attracting males is a way to bring food to females during the mating season. While there are some systems where males clearly sacrifice themselves (black widows, for example), it’s clear that the male is not a willing participant in this particular cannibalistic partnership.
Females signal to males using pheromones, and well-fed females tend to attract more males. For males, approaching females represents a legitimate risk of cannibalism. Thus, they tend to choose well fed females over leaner females because females who have eaten are less likely to eat them. They also gauge risk while approaching females by approaching leaner females more slowly, and staying further away while determining whether a prospective mate is likely to kill them. Males who are caught by females also appear to resist being eaten. Males are very picky and cautious when approaching females. Even though there’s only a 20-30% chance they’ll be eaten, mating is still a very risky proposition.
In essence, the mantis mating system doesn’t resemble what you see in the video. The female doesn’t need to kill the male, and this happenstance is a lot more rare than many believe. In many cases, cannibalism is the result of simply keeping the male in an enclosed space with a hungry female. However, cannibalism does happen in the wild and it appears to be an important source of mortality for male mantids.
This system also upends a lot of what people believe about animal sexuality. Here’s where we get back to Bateman’s rule. Mantids upend Bateman’s assumptions: males are extremely choosy about females and are cautious about who they approach, while females mate with virtually any male willing to risk an encounter. This sort of ‘choosy male’, ‘unfussy’ female system certainly isn’t how a lot of people think about gender conflict…but it’s a great example of how nature seems to ignore what we assume.
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