Male pygmy squid (Idiosepius paradoxus) attach their spermatophores to the outside of their partner’s body, and multiple males can make such deposits.

This leaves females with the choice of which spermatophore to accept, and they show a distinct preference for the sperm packets that come from small males.

This is surprising, given what we know about large, dominant males and females’ general inclination towards them.

But small-statured males are much faster in their spermatophore deposition than large ones. A large spermatophore from a large male is going to take longer to extrude and deposit. It is thought that females prefer the small ones to decrease their risk of predation during deposition.

During sperm transfer, males and females are effectively affixed together, making them twice as noticeable to fish-predators (not to mention being in an awkward copulatory state and unable to react quickly).

It therefore follows that females would be more apt to accept a quick sperm gift than a slow one, for both her immediate survival and the survival of her potential offspring (her sons will be more likely to be small, and preferred).

What do females do with the unwanted spermatophores?

Usually they eat them. That’s one high-protein snack!

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This is an adapted excerpt from my book “Wild Sex: The Science Behind Mating In The Animal Kingdom“