Sixteen legs, all told, are involved in the kind of one-on-one sexual activity celebrated in this new study:
“Here, we bring [report] 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.”
Daniel Oberhaus wrote an appreciative essay about this in Motherboard.
This adds to the list of species eagerly observed, by humans, to engage in oral sex. Among the very most celebrated: The 2010 Ig Nobel Prize for biology was awarded to Libiao Zhang, Min Tan, Guangjian Zhu, Jianping Ye, Tiyu Hong, Shanyi Zhou, and Shuyi Zhang of China, and Gareth Jones of the University of Bristol, UK, for scientifically documenting fellatio in fruit bats. Their report about that is; “Fellatio by Fruit Bats Prolongs Copulation Time,” Min Tan, Gareth Jones, Guangjian Zhu, Jianping Ye, Tiyu Hong, Shanyi Zhou, Shuyi Zhang and Libiao Zhang, PLoS ONE, vol. 4, no. 10, e7595. Here is video of that:
Ed Yong, a specialist in this line of research, published an appreciative essay in 2013 on that fruit bat paper and on a subsequent, related discovery: “You’ve Seen Fruit Bat Fellatio. Now: Fruit Bat Cunnilingus.”