The Secret To Attracting A Partner? The Smell Of Cheesy Feet – At Least, If You’re A Black Widow

Attracting a mate in the animal world is of prime importance, but how best to go about it? Do you flash your feathers in a personalized dance, fight your rivals for the chance to breed, or, in the recently discovered web of widow spiders, follow the smell of cheesy feet?

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The western black widow (Latrodectus hesperus) is a well-studied spider with a breeding season that runs through the summer months. Typically, females survive the season and go on to mate the following year. Most males, however, die after a single season. For a male to find a female, he must follow the airborne pheromones that are given off by her web. 

Arriving at the web and making direct contact with the pheromones on it triggers the males to engage in courtship behaviors. This involves “web bundling”, whereby the male will cut sections of the female's web and bundle it together with his own silk. This helps the female know that the male is not a prey species tangled in the web and reduces female aggression. For the male, it has the added benefit of making the female's web less attractive to other males.

To study whether the pheromones are produced seasonally, or have different effects when created in a lab, the team devised many experiments, including different behavior studies and a year-long field experiment in which the team collected webs monthly before analyzing the chemicals present on the webs and comparing them throughout the year. The team also created lab-made versions of the pheromones, which worked to attract male spiders, though spider-made pheromones led to longer courtship behaviors. 

Interestingly, spider pheromones are not well studied and only a handful are known. The chemical compound N-3-methylbutanoyl-O-methylpropanoyl-L-serine methyl ester (dubbed "1") is a known contact pheromone component, but in investigating the western widow, researchers identified another one: N-3-methylbutanoyl-O-methylpropanoyl-L-serine (7). The combination of these, to human noses at least, apparently smells like cheesy feet. 

"The black widows demonstrate astonishingly sophisticated communication skills: with a complex chemical interplay of flavours and odours, the females significantly increase their chances of successful mating," said first author Dr Andreas Fischer from the University of Greifswald in a statement.

As well as discovering that isobutyric acid – which is released in the breakdown of 1 and 7 – is yet another male-attractant pheromone component, the research revealed that female western black widow spiders produce greater amounts of 1 and 7 during the warm summer months than in the spring and fall. This follows the fact that there are more sexually mature males available to breed in the summer, hence the need to produce larger quantities in those months. 

"What I found particularly exciting about the results was that the females adapt the intensity of their scent signals to the time of year," continued Fischer. "Although they lure males all year round, they are most attractive when most males are looking for a mate."

The study is published in the Journal of Chemical Ecology.