Male specimens of the Madagascar Darwin's bark spider are several times smaller than the females. Here, a pair a seen mating. Photo by ZRC SAZU

Male specimens of the Madagascar Darwin's bark spider are several times smaller than the females. Scientists observed them regularly salivating on female genitals. Photo by ZRC SAZU

Male specimens of the Madagascar Darwin's bark spider are several times smaller than the females. Scientists observed them regularly salivating on female genitals. Photo by ZRC SAZU

LJUBLJANA, Slovenia, April 29 (UPI) -- A new study highlights an exceedingly rare occurrence -- oral sexual encounters among spiders.

The discovery was made by a team of biologists from the Scientific Research Centre of the Slovenian Academy of Sciences and Arts, or ZRC SAZU.


During field studies, researchers observed male specimens of the Madagascar Darwin's bark spider, Caerostris darwini, regularly salivating onto female genitalia.

The oral sex act was just one of several unusual sexual behaviors detailed by the research team in a new paper, published this week in the journal Scientific Reports.

The species also exhibited sexual cannibalism and genital mutilation behaviors. Previous studies have shown the species' web to be largest in the natural world -- and their silk the toughest.

Male specimens of the Darwin's bark spider are several times smaller than the females.

"Oral sexual contact seems to be an obligate sexual behavior in this species as all males did it before, in between, and after copulations, even up to 100 times." Matjaž Gregorič, a research associate at ZRC SAZU, said in a news release.

Though not common, oral sex acts have been observed among macaques, lemurs, bonobos, hyenas, cheetahs, lions, dolphins and bats, but the behavior is extremely rare among spiders.

Researchers hypothesize that the behavior is performed as a way to boost a male's chance of gaining a sexual mate and producing offspring, either by proving his sexual worth or encouraging a chemical environment that improves the viability of his sperm.