The researchers uncovered this mating behaviour while studying the Madagascan Darwin’s bark spider (Caerostris darwini) from Madagascar.
Females of this spider species are several times larger and heavier than males.
“Oral sexual contact seems to be an obligate sexual behaviour in this species as all males did it before, in between, and after copulation, even up to 100 times,” said lead researcher Matjaz Gregoric, research associate at the Scientific Research Centre of the Slovenian Academy of Sciences and Arts.
Gregoric led the field and laboratory work that resulted in the publication of the study in the journal Scientific Reports.
Oral sexual contact is rare in the animal kingdom, except in mammals, where fellatio-like behaviours are known in macaques, lemurs, bonobos, hyenas, cheetahs, lions, dolphins and bats. However, cunnilingus-like behaviours, like the one shown in this spider are even rarer.
The researchers suggest that in this spider species oral sexual encounters could be a mechanism for boosting the male’s chances of paternity by either signalling the male’s quality or creating a chemical environment that would favour one male’s sperm against the sperm of rival males.