Male nursery web spiders often woo potential lady-friends with gifts wrapped in silk. Mating may ensue, during which a female unspools the present, expecting to find a tasty treat. But the males can be unscrupulous. Some offerings contain inedible plant seeds or empty insect exoskeletons.

How do males get away with such egregious behavior?

Researchers provided males with potential gifts—either a fly or an inedible item, such as a bit of cotton. Other males had to give it a shot with no gift at all.

The empty-handed males were mostly unsuccessful at mating. Whereas those with a gift could get the girl. But if the gift was worthless, the females quickly realized the deceit and pushed the copulating males off. Which gave the males less time to transfer sperm.

The study is in the journal BMC Evolutionary Biology. [Maria J. Albo et al., "Worthless donations: male deception and female counter play in a nuptial gift-giving spider"]

Females clearly prefer males bearing edible presents. But some males know they can get limited action without expending the energy on a real gift. And the females laid almost the same amount of eggs fertilized by males bearing real or phony gifts. With both strategies successful, the behavior gets maintained. And the species stays stocked with deadbeat dads.

—Cynthia Graber

[The above text is a transcript of this podcast.]

Image of nursery web spiders (Pisaura mirabilis) with gift courtesy of Maria J Albo