To lure in a mate, female spiders can make their webs more attractive, research shows

Some female spiders may be able to adjust their webs to make them appear more sexually attractive to male spiders, researchers at Simon Fraser University have found.

In a recent article published in the journal Communications Biology, doctoral student Andreas Fischer and fellow scientists say they have discovered that female false black widows — female steatoda grossa — have an enzyme that breaks down compounds on their web, affecting its taste, to seduce male spiders.

They also found that female false widows are able to regulate this process depending on how much they're calling for male spiders.

Unlike black widows, which have a bright red hourglass mark on their body, false widows do not have coloured markings.

Female spiders use scent, or pheromones, to attract male spiders, Fischer explains, adding that they looked at this component in their study.

"They use smell, and taste, to lure each other in or to tell each other to go away, so we started identifying the chemicals involved in this process," Fischer said on CBC's Daybreak South.

Studying the webs of 93 sexually mature, adult virgin female spiders, and that of 70 juvenile females for comparison, the researchers found that female false widows seem to have an enzyme that adjusts their pheromones to attract males.

It isn't known, however, how the brains of male spiders process smell, Fischer says.

"I guess we don't know the same thing for humans," he said.

"But either way, we know that they get attracted to those very specific chemicals which are species-specific."

Stuart Brown, a self-described amateur entomologist, says just like spiders, many other invertebrates — such as ants and scorpions — have poor vision and have to rely on pheromones to convey sexual interest and other messages critical to survival.

"If there's an ant that wanders out to an area that's dangerous, they will leave a scent trail that says, 'Stay away from this,'" said Brown, who also owns a pet shop in Lake Country, B.C., about 23 kilometres north of Kelowna.

"If they find food, they go, 'Hey, follow this trail! There's food over here.'"

SFU biological sciences professor Gerhard Gries, who supervises Fischer's research, says the study is significant because sexual communication among spiders has remained underinvestigated.

"How on earth do they manage to sense these sex-attractive pheromone components that are disseminating from the female threads? We have no idea," Gries said.

"So there are very significant knowledge gaps when it comes to communication ecology of web-building spiders."

Gries says the researchers' next step is to study whether females in other spider species can also manipulate their webs to lure males.

He adds that another subject of interest is whether adult, non-virgin female spiders can adjust their webs to signal to males that they are younger, virgin spiders.

After mating, female false widows can lay three or more cocoons, each containing 200 eggs that hatch within two to four months. Males die shortly after mating.