Male black widow spiders on the prowl to mate (and sometimes be victims of black widow cannibalism by females, thus the name Latrodectus mactans) shake their abdomens to produce carefully pitched vibrations and avoid potential attacks by females – who otherwise may misinterpret the advances as the vibrations of prey.
They want her to know they are a male and not a meal. If you read this and know who Miley Cyrus is, they basically twerk.
The team recorded the vibrations made by male black widow spiders (Latrodectus hesperus), hobo spiders (Tegenaria agrestis) and prey insects.
Co-author Catherine Scott. a graduate student at Simon Fraser University, says, "The web functions as an extension of the spider's exquisitely tuned sensory system, allowing her to very quickly detect and respond to prey coming into contact with her silk. This presents prospective mates with a real challenge when they first arrive at a female's web: they need to signal their presence and desirability, without triggering the female's predatory response."
The researchers found that the courtship vibrations of both species differed from those of prey, but that the very low-amplitude vibratory signals produced when male black widows shake their abdomens were particularly distinctive. "These 'whispers' may help to avoid potential attacks from the females they are wooing," explains Scott.
Citation: Samantha Vibert, Catherine Scott and Gerhard Gries, 'A meal or a male: the 'whispers' of black widow males do not trigger a predatory response in females', Frontiers in Zoology 2014, 11:4 doi:10.1186/1742-9994-11-4