False widow spiders use pheromones to manipulate mates

False widow spiders (Steatoda grossa) are a globally invasive species capable of reproducing year-round. However, little is known about the reproductive behavior of this common species of spider, colloquially known as the cupboard spider, due to its tendency to predominantly live in buildings. 

Now, a recent study led by Simon Fraser University has revealed how female spiders communicate by using pheromones to construct more attractive webs in order to lure mate-seeking males. According to the experts, these females disseminate pheromones from their webs to attract males and deposit contact pheromone components on their webs that induce courtship by the males once they arrive. In addition, the researchers also identified the organ that produces these pheromones (the posterior aggregate silk gland), as well as the chemical structure of the pheromones involved in courtship behavior.

“We also found that female false widow spiders have a sophisticated method to constantly ‘mate call’ by slowly breaking down the courtship-inducing pheromone components to sex attractant pheromone components that lures the males in,” said study lead author Andreas Fischer, a doctoral student in Biology at Simon Fraser.

The scientists compared 93 sexually mature, adult virgin female false widow spiders that spun webs on wooden triangular prism scaffolds or bamboo skewers with 70 immature sub-adult females that were also allowed to build webs. Then, they collected web samples and identified their pheromone components, while testing the webs’ ability to attract and induce courtship behavior in male spiders.

The analysis revealed that females are able to actively adjust the attractiveness of their webs to males, by fine-tuning the pH level in their silk and thus controlling the enzyme involved in the transition of contact, courtship-inducing pheromone components to mate attractant pheromone components.

This, while previously only insects were known to actively time pheromone production and dissemination, and to modulate the amount of pheromones they emit, these findings suggest that arachnids, such as web-building spiders, could also be capable of such amazing feats.

The study is published in the journal Nature Communications Biology.

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By Andrei Ionescu, Earth.com Staff Writer