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New data has been unraveled in studies concerned with determining why female spiders so often practice cannibalism on their male counterparts. For years, hypotheses have been postulated and discarded nearly as quickly as research could be conducted in efforts to explain this strange phenomenon. Now, some scientists have concluded the answer may be less extraordinary than previously speculated.
Research gathered by students from Miami University in Ohio was able to conclude sexual cannibalism was directly correlated to size in at least one species of arachnid. Female members of Hogna helluo, a species of wolf spider, frequently feasted on males much smaller than themselves. The students involved in the study, Shawn Wilder and Ann Rypstra, cross-referenced their data with older publications on different spider species and found this to be a widespread detail. In these populations of spiders, sexual cannibalism would appear to be a byproduct of the evolution of the species.
In other species of spiders, cannibalism is linked more closely to the disposition of the female spider. Investigations at the Experimental Station of Arid Zones (EEZA-CSIC) found some female tarantulas would consume the males prior to sexual intercourse, negating the fertilization of their eggs. Genetics were called into play in order to determine why the females had a tendency to hunt males as if they were prey. The team of researchers offered males selected at random to female virgins in order to gauge their reactions. The study found that aggressive genes vary from spider to spider, with some females retaining their hostile demeanor while both feeding on prey and engaging in copulation, while others remained docile regardless of activity. The information suggests personalities differ amongst spiders, and fluctuating levels of aggressiveness in females would directly contribute to the success of males reproducing. Contrary to the research acquired in the study on Hogna helluo, it was also discovered that size had no direct influence on cannibalism among the tarantulas.
Other new data unraveled in extrapolating the causation of cannibalism in spiders suggests the potential for healthy offspring may be a contributing factor. In Argiope bruennichi, a species of orb-web spider, females immediately snatch and constrict males during sex in order to feed upon them mid-coitus. Only about 30 percent of the males survive this encounter, but those which allow the females to snack on them are able to prolong the session, ensuring the eggs are inseminated. Roughly half of the survivors will seek to impregnate another female afterwards. A researcher in the study, Klaas Welke, stated the males may be directly concerned with the survival of their children. According to Welke, the behavior of the males could be a “paternal investment into their own offspring, and they provide females with nutrients.”
Cannibalism in spider populations has long been a topic for debate, but new data is being unraveled due to recent studies. For years, it has been a guessing game in knowing whether a female would choose to eat a male or mate with him. Copulation has proven to be a risky business for the males, but at least now researchers are closer than ever to understanding why this is the case.
By Sam Williams