Nothing says love like chewed-up body parts—at least for nursery-web spiders (Pisaura mirabilis). In some populations of these European arachnids, females won't mate with males unless the suitors present a gift of dead insects wrapped in silk. Males carry their bundles as they search for mates, but it's unclear how that extra baggage affects their running and fighting abilities. There's also been the question of whether the eight-legged Casanovas cheat by including inedible objects or dried-out food in their gifts to make them appear larger.
By capturing 58 male nursery-web spiders in the wild, researchers have now addressed both issues in a study published online this month in Animal Behaviour. They found that 23 of those males had gifts, all of them containing parts of freshly-killed insects. In laboratory combat trials, male spiders with gifts weren't hampered in their fights with gift-free rivals, although some dominant males with and without gifts stole gifts from weaker males. The bundles did compromise male running abilities in timed laboratory trials, slowing the spiders by about 42% compared with similarly sized males without gifts.
This is the first study demonstrating transportation costs for gift-carrying in insects and spiders. The team speculates that this labor of love advertises a male's ability to find food and to hang on to it.
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