Spiders rely heavily on chemical signals to navigate their world, using a form of communication often misinterpreted as a sense of smell. Their attractions are based on biological necessity for survival and reproduction, not preference. These arachnids are primarily attuned to chemical molecules that signal two things: a potential mate or the location of their next meal. Unlike mammals, spiders use a decentralized sensory system to detect these airborne and contact-based chemical messages.
How Spiders Detect Odors
Spiders perceive their chemical environment through specialized sensory structures located primarily on their legs and pedipalps. The detection of airborne chemicals, analogous to smelling, is accomplished by fine, hair-like structures called wall-pore sensilla. These sensilla contain pores through which volatile molecules can pass, stimulating the underlying sensory neurons.
Recent research identified these olfactory hairs on the walking legs of certain male spiders, demonstrating their function in detecting airborne sex pheromones. Spiders also possess chemoreceptors that function as contact sensors, which is more like tasting what they touch. These receptors, located on the tips of the legs and pedipalps, detect non-volatile chemical cues deposited on surfaces like silk or the ground. This dual system allows them to process chemical information both from a distance and upon direct physical contact.
Chemical Signals for Mating
The most significant chemical signal a spider is attracted to is the sex pheromone released by a conspecific female. Females release these compounds to communicate their reproductive status and species identity to males. These chemical signals are often lipid-soluble compounds released as airborne molecules to attract a male from a distance.
In many web-building species, the female deposits non-volatile pheromone components onto her silk draglines or web structure. Males follow this chemical trail, using chemoreceptors to confirm the female’s identity and readiness to mate upon contact. For example, the volatile sex pheromone of the female wasp spider, Argiope bruennichi, draws males to her location. The ability to detect these chemical signatures is so crucial that specialized wall-pore sensilla are found in higher density on adult males seeking a mate.
Scents That Indicate Food Sources
Spiders are drawn to chemical cues that signal the presence of prey, often detecting the byproducts of insect activity rather than the insects themselves. One method involves volatile organic compounds (VOCs) released by decaying organic matter. Certain orb-weaving spiders incorporate debris into their webs, which attracts flies and other insects that feed on decay. The spider is not attracted to the scent of decay directly, but to the resulting influx of prey species.
Another attraction method involves the chemical distress signals of plants under attack by herbivores. When insects feed on crops, the damaged plant releases specific compounds, including methyl salicylate and linalool. Wolf spiders, which are active hunters, are attracted to these herbivore-induced plant volatiles (HIPVs) because the scent reliably indicates where their insect prey is concentrated. This is an indirect but effective chemical indicator of a food source.
In a few specialized species, the attraction is more direct, involving chemical mimicry of the prey’s own communication system. The Bolas spider, for instance, releases volatile chemicals that mimic the sex pheromones of female moths. This scent acts as a lure, drawing unsuspecting male moths directly into the spider’s single, sticky silk line.