Female spear squid mate willingly only with big males, which court the females with natural, multicolored, pulsating lights—bioluminescent mating displays that the smaller males don't exhibit.

Once the female selects a male, he holds her above him and inserts his arm, holding a sperm packet, into her oviduct, a passage through which his sperm travels to her ovaries. He'll then watch over her until she spawns to try to ensure no other males fertilize her eggs.

Yet just as the female begins to lay her eggs on the seabed, a smaller squid, a sneaker, may dart over and mate with her head-to-head. (See squid pictures.)

A female is typically "willing to accept sneaky matings, as she has a specific sperm storage organ