Image: Flickr/EOL Learning and Education Group

Darwin's bark spiders are hands down the best spiders: they make giant webs that can span 25-meter-wide rivers, their silk is one of the strongest materials known to man, and, according to this study, male Darwin's bark spiders give their mates oral sex. That is, if you define oral sex as "salivat[ing] onto female genitalia pre-, during, and post-copulation." I know I do.

Spider behaviors include oral sexual encounters. "Several clades of spiders whose females evolved giant sizes are known for extreme sexual behaviors such as sexual cannibalism, opportunistic mating, mate-binding, genital mutilation, plugging, and emasculation. However, these behaviors have only been tested in a handful of size dimorphic spiders. Here, we bring another lineage into the picture by reporting on sexual behavior of Darwin's bark spider, Caerostris darwini. This sexually size dimorphic Madagascan species is known for extreme web gigantism and for producing the world's toughest biomaterial. Our field and laboratory study uncovers a rich sexual repertoire that predictably involves cannibalism, genital mutilation, male preference for teneral females, and emasculation. Surprisingly, C. darwini males engage in oral sexual encounters, rarely reported outside mammals. Irrespective of female's age or mating status males salivate onto female genitalia pre-, during, and post-copulation. While its adaptive significance is elusive, oral sexual contact in spiders may signal male quality or reduce sperm competition." Related content: In beetles, it’s the female genitalia that need to be hard.To avoid sexual cannibalism, praying mantis males choose well-fed females.Study finds that male fiddler crabs are a**holes.