Prey or Mate – Can web-building spiders tell the difference?
Featured Image Caption: Web-building spiders build webs to sense when and where prey land, but females must decipher mate from prey (Image Source: “015 – spider web” by alanreeves001 is marked with CC BY 2.0.).
Reference: Wignall, A. E. & Herberstein, M. E. (2022). Male courtship reduces the risk of female aggression in web-building spiders but varies in structure. Behavioral Ecology, 33(1), 280-287. https://doi.org/10.1093/beheco/arab140
The Quest for a Mate
As temperatures begin to warm, young spiders will start to emerge after a long winter. Casting their silken balloons, the newly hatched spiders disperse far and wide, carried by the wind. After settling in a cozy spot, web-building spiders build their first web. The web acts as a net to trap prey and alert spiders of their next meal. Spiders are very sensitive to vibrations, so the web allows them to determine when and where the prey has fallen to attack before the meal escapes. Once mature, males leave their webs to search for a mate – all while braving predators, harsh conditions, and no food on the journey. Guided only by scent and silk trails, finding a female may not be the toughest challenge males will face. If a female misidentifies the male for prey, the consequences could be dreadful, making this no ordinary love story.
Many spiders do not have very good eyesight and rely heavily on other forms of sensory information, such as vibrations. When a male reaches a female’s web, the vibrations the male causes are similar to the vibrations prey make. The female, not wanting to risk losing a meal, could make false judgments if the male cannot identify itself in a matter of seconds. Talk about a stressful first date! Insects vibrate the web randomly and vigorously. To avoid being mistaken for prey, males must produce vibrations that are vastly different. Arachnologists (scientists who study arachnids, including spiders) have found that males do just that by producing patterned and repetitive vibrations. For example, if a letter is a unique vibration, a spider might produce vibrations like A-A-B-B-A-A-B-B whereas prey would produce D-C-B-E-A.
Please Don’t Eat Me!
With their prey-capturing expertise, spiders are essential for keeping pest populations in check. One estimate suggests that spiders worldwide consume up to 800 million tons of prey each year! To continue this vital role, females must determine whether a vibration is prey or a mate. While females must be fast to capture prey before it escapes, accidentally eating a mate would not allow them to reproduce and contribute to the next generation.
Arachnologists Dr. Anne Wignall and Dr. Marie Herberstein wanted to test whether females can differentiate a male from prey. They collected Trichonephila plumipes (commonly known as the tiger spider) from areas in Australia. The researchers placed a live cricket (prey) on the web of a female while playing male vibrations from the same species, white noise vibrations, or no vibrations. Females responded to cricket vibrations quickly when no other vibrations were played but delayed their response when they sensed the same species of male vibrations. Thus, females can quickly decipher prey from a mate.
Upon reaching a female’s web, the first goal is to avoid being mistaken for prey, but the second goal is to communicate the species. If the male entering the web is not the same species as the female, the female might eat the visitor because mating would not produce offspring. The arachnologists set up a similar experiment to see if females can confirm that the male is the same species. The researchers presented tiger spider females with male vibrations from Argiope keyserlingi (St. Andrew’s Cross Spider). Females responded equally to the cricket when presented vibrations from a different species or no vibrations. The researchers concluded that females can quickly identify whether a male is of the same or different species.
First Impressions Are Everything
Tiger spider females delayed their response to same species male vibrations, but not for different species male vibrations, white noise vibrations, or silence. Male web-building spiders have adapted to producing unique, repetitive vibrations when entering a female’s web to ensure they will not be mistaken for prey or a different species. Females have evolved to identify male courters and delay their response to prey. The use of vibrations by male web-building spiders is widespread – occurring in at least 34 species of spiders from eight different spider families. Vibration structure varies widely by species, allowing females to determine whether the male courter is the same species. The structure can vary based on spider size, web properties, and how the vibration is produced: by drumming, rubbing body parts together, plucking, or shaking.
Once the male has identified itself as a potential mate and the female has delayed attack, males are still not out of the woods. Male vibrations delayed but did not prevent attacks. The male and female still need to decide if the other is a quality mate before mating occurs. While this may be no ordinary love story, mating will produce the next generation of pest controllers and quality mates, allowing this remarkable cycle to continue for years to come.
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