Arachnid love: Female wolf spiders use dragline silk to snag a mate

Sometimes a lady spider has to show off the goods. New research shows that female wolf spiders increase their dragline silk advertisements to get otherwise uninterested males’ attention.

“Previous studies have assumed that females passively produce [silk] and that males then exploit these cues to search for and locate the female,” Susquehanna University biology professor Matthew H. Persons of Susquehanna University told “We were interested to know what kinds of silk females are making and if they change how much or what kinds when they see males in the area, or if they change how much or what kinds they make based on what the male is doing.”

For their research, Persons and his team scoured corn and soybean fields for wolf spiders. Apparently they’re not hard to find — Persons has been known to collect up to a hundred an hour on a good day. Persons co-authored the study that appeared in the November 2014 issue of “Ethology.”

“Most of the time you can collect about 50 per hour and you only need to step a couple of feet into the edge of a soybean or corn field to do it,” he said. “For this study, I think it took maybe a couple of afternoons to collect our study subjects.”

In the end, he and his team collected 78 adult males and 156 subadult female wolf spiders in the fields surrounding Susquehanna University’s Snyder County, Pa.  If you have arachnophobia, it sounds like you may want to avoid corn and soybean fields as a general rule of thumb.

“During the dispersal phase with ‘spiderlings’ leaving their mother, we’ve measured densities as high as 16 individuals per square meter of crop land. These little guys will run across your shoes if you stand in a field during the summer,” Persons added.

Once their eight-legged subjects were rounded up, the team separated the boys and girls and placed them in petri dishes arranged concentrically.

Persons said that females put in a petri dish were then placed inside a larger “arena” that contained a “male that they could see but not touch.”

“Some of the males had access to female silk and would court vigorously (the courting male treatment). Other males didn’t have access to female silk and so didn’t court much (non-courting treatment). We then measured the kinds of silk and how much females deposited on the ground while watching these males,” he added.

Curiously, they observed that the female spiders were mostly interested in attracting male attention when the males were ignoring them.

“What we found was that females produced a lot more silk when they watched males that were not courting compared to when they were. This indicates that they are using silk to try to get a male’s attention,” he said.

Persons said that the females deposited three different kinds of silk — dragline silk, cord silk, and attachment disks — that probably each correspond to a different kind of communication.

For instance, when dealing with males that show little-to-no courtship, the females will produce more dragline silk while producing less cord silk. Males will then court more and more intensely when in contact with female cues.

According to Persons, this new research has important implications, not just for the study of spiders, but for how researchers can understand sexual communication between animals in general. While in the past it was often believed that males were the pursuers while the females played “coy”, the research indicates that there is a simultaneous court-and-choose scenario at play.

“Females of many species produce sex pheromones,” Persons said. “These cues are used by males to locate females and induce them to court. Most studies think about female sex pheromones as a cue that females are passively producing. In other words, they produce it at a constant rate and continuously once they are receptive to mating and males, then ‘exploit’ this cue to find them.”

Persons said that his team’s study shows that sex pheromones, or in this instance, female-produced silk, aren’t produced at a constant rate. Instead, this silk production is dependent entirely on the male’s actions. Essentially, these female spiders are actively seeking out mates. The silk isn’t “a passive cue for males,” but rather an “active sexual advertisement or courtship signal that females are sending to males,” Persons said.

This is changing the way researchers view the mating habits of spiders. Persons said it’s all about the chemicals.

“Maybe it isn’t males searching and finding females, courting hard and then females picking the best male … but rather pheromones serving as ‘chemical courtship’ where females chemically ‘display’ to males their qualities,” he said. “Males and females are courting each other but are using different sensory channels to do it … They are then mutually selecting each other based on the information they are getting from the other.”

Arachnophobes take note – no researcher was bitten after handling all of these spiders. In fact, wolf spiders (despite their frightening appearance) aren’t aggressive, Persons asserted.

“I’ve been doing research on wolf spiders for nearly 25 years and have conservatively handled at least 50,000 of them and have only been bitten once by a different species of wolf spider than the one used in this study,” he said. “This single bite was the result of an interview with a journalist where I was specifically demonstrating to a journalist just how unwilling wolf spiders are to bite people. I had to poke and prod the spider with my finger, physically exhaust it, then corner it. Eventually after running out of alternatives, she turned around and bit me. In other words, based on my own personal experiences with them (and I’ve had a lot), wolf spider bites are extremely uncommon.”

Persons said people shouldn’t be so scared of spiders, in general.

“I’m generally pretty skeptical of reports of spider bites and wolf spider bites in particular,” he said. “If anyone deserves to be bitten, I’m probably one of them, but I’m still waiting.”