Nature has published an article about a cave insect that combines the words “marathon sex session” with “the female’s spiky penis”:
In desolate caves throughout Brazil live insects that copulate for days, the female’s penetrating erectile organ sticking fast in a reluctant male’s genital chamber until he offers a gift of nutritious semen. Neotrogla seems to be unique among species with reversed sex roles — with choosy males and aggressive, promiscuous females — in also having swapped anatomy….
When the flea-sized winged insects mate, the female mounts the male and penetrates deep into a thin genital opening in his back. Membranes in her organ swell to lock her in, and multiple spiky spines act as grappling hooks to anchor her tightly to the male. (When researchers tried to pull apart two mating insects, the female was gripping so tightly that the male was accidentally ripped in half, leaving his genitalia still attached to the female.) The tip of the female’s penis fits neatly into the male’s genitalia to allow her to receive a large, teardrop-shaped sperm capsule over their 40–70 hours of copulation.
The key to the anatomy and role reversal might be simple hunger. Neotrogla species live in extremely dry caves, says Ferreira, where there is not much in the way of food, save for bat guano and the occasional dead bat. A female needs enough nourishment to make eggs and reproduce, though, so she likely found another source of nutrition, [entomologist Kazunori] Yoshizawa [of Hokkaido University in Japan] says: her mate’s semen capsule.