Out of Sight

More than a pretty shell: Female crabs
rely on a chemical cues when choosing a mate.

When Alicia Keys sang "Love Is Blind," she probably wasn't thinking about female blue crabs. Turns out she might as well have been. A pair of Duke researchers has discovered that female blue crabs literally are blind when choosing a mate.

Like many crustacean species, blue crabs undergo molting and mating at the same time, and because the multifaceted lenses that make up the crabs' eyes are part of the exoskeleton, they too are shed. This means that during the critical time of mating, when male blue crabs roll out their array of courtship rituals—including waving their claws, standing tall on their walking legs, and rhythmically moving their swim paddles—females can't see a thing. They've taken out their contact lenses.

Sönke Johnsen, an associate professor of biology, and graduate student Jamie Baldwin confirmed this by subjecting molting females to a crab eye exam, featuring a rotating, blackand- white-striped drum. Typically, crabs moved their eyes in the same direction as the rotating stripes. Shortly after molting, however, females don't track the stripes at all.

The males can see just fine, and in fact use their color vision to choose females with red claws as opposed to other hues. But Baldwin and Johnsen say female blue crabs aren't completely clueless about their blind dates. They believe that chemical cues, what we would call smell, may help overcome blurred vision.