In another study, UC postdoctoral researcher Alex Sweger examined the way male wolf spiders use vibrations to woo females. Spiders don’t have ears but can “hear” with tiny sensory organs on their legs that pick up the faint vibrations of prey. Male spiders use a special rasping organ on their pedipalps to produce vibrations that drum the ground, rattling leaves or soil, as part of their ritual mating dance.



Sweger used a laser Doppler vibrometer to measure the spider’s vibrations and reproduce them with a device called a piezoelectric disc bender.



“It’s very similar to the vibrations made by an actual spider. We calibrate the device and attach it to a leaf and see how the female spider responds,” he said.



The ruse works.



Sweger suspected that summer rains are the bane of these spider drummers. He found that males tried to woo females regardless of the weather. But when the ground is wet, they rely more on their visual cues — waving their forelegs in a dance that only female wolf spiders might appreciate.



“They shift to visual behaviors over vibrations on wet leaves, suggesting they are flexible in using different communication modes to suit the conditions,” Sweger said.



Even so, males have far less mating success under wet conditions.



“Their breeding season isn’t very long. Males have a lot of pressure to mate with as many females as possible to increase their genetic success,” Sweger said. “So if you can overcome a hurdle like rain rather than wait for ideal conditions, it benefits you.”



