For some spider suitors, the arachnid equivalent of a box of chocolates is an insect wrapped in silk. New research shows it's not just the gift but also the color of the wrapping that can seal the deal among one species.

Male spiders of the species Paratrechalea ornate reveal their health and suitability as a mate by the whiteness of their gift wrap, a new study suggests.

"Females evaluate the physical condition of a male based on his silk wrapping performance, and how the gifts he brings look," study researcher Mariana Trillo, of Uruguay's Instituto de Investigaciones Biológicas Clemente Estable, said in a statement. "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."

Trillo and colleagues conducted experiments with semi-aquatic Paratrechalea ornate spiders collected from the Santa Lucia River in Uruguay. During one test, the scientists painted the mouth parts of some of the male spiders white. (The spiders carry their nuptial gifts in their mouth parts.) The females paid more attention to the male spiders with painted mouths. They also mated with the painted males earlier and more often than the males without paint.

The scientists think their results suggest the white coloring of the silk is the main draw for female spiders. Because this species is most active during sunset and at night, white silk is easier to see over long distances. What's more, males in better physical shape produced whiter gifts, because they used more silk in their wrapping, while the poor wrapping job of less healthy males resulted in a duller package. This means the color of the gifts could be a reflection of the male's body condition, which could help the females judge their suitors, the scientists say in the journal Naturwissenschaften.

For other kinds of spiders, silk wrapping can serve as a disguise for a worthless gift. A study from 2011 in the journal BMC Evolutionary Biology showed that some males of the species Pisaura mirabilis, will wrap an ant husk or cotton in silk. Often, by the time the female had examined the decoy gift, the male had already had his way with her.

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