Spider females choose males best at wrapping 'wedding gift'

South American spider females pick their mates based on how well a "wedding gift" of prey is wrapped, white silk and all, researchers say. Paratrechalea ornate, a South American semi-aquatic spider, is one of many animals and especially invertebrates that use nuptial gift-giving during courtship and mating, they said. During mate searching, males of this species walk with vibrating forelegs and feelers while carrying prey wrapped in white silk in their mouth parts. To investigate this behavior, researchers at the Instituto de Investigaciones Biologicas Clemente Estable in Uruguay collected spiders from the country's Santa Lucia River in Uruguay and ran a set of experiments in their laboratory in Montevideo. In one experiment, the mouth parts of some males were painted white, and others not. Females exposed to painted males were more active, showed more physical contact, spent more time in front of them and accepted the matings earlier and with more frequency than those exposed to males without paint, they found. The white coloring of the silk "gift-wrap," rather than the gift itself, holds the big appeal for female spiders, the researchers said they believed. "Females evaluate the physical condition of a male based on his silk wrapping performance, and how the gifts he brings look," researcher Mariana Trillo said. "Also, silk wrapping is a condition-dependent trait and most probably allows a Paratrechalea ornata female to acquire information about her potential mate, including body condition and quality."