Spiders Detect Smells Through Leg Hairs, Claims New Study

New research has revealed that spiders use specialised hairs on their legs to detect airborne scents, offering fresh insights into the sensory abilities of these arachnids. This discovery has resolved a long-standing question about how spiders, which lack antennae like insects, can identify odours such as pheromones. Male spiders were observed using olfactory hairs, known as wall-pore sensilla, to sense sex pheromones emitted by females. This mechanism underscores their ability to locate potential mates through chemical signals.

Olfactory Sensilla Identified

According to a study, published in the Proceedings of the National Academy of Sciences, the wall-pore sensilla were found on the upper legs of adult male wasp spiders (Argiope bruennichi). These microscopic structures are believed to be critical for detecting pheromones. High-resolution scanning electron microscopy revealed thousands of these sensilla, which were absent in females and juvenile males. This specific distribution supports their role in mate detection. Researchers emphasised to phys.org that these findings have mapped and identified the elusive sensilla, previously thought to be absent in spiders.

Response to Pheromones

Experiments demonstrated the sensitivity of these sensilla to pheromone compounds. Tiny amounts of the substance, such as 20 nanograms, elicited significant neuronal responses. The experiments involved exposing the sensilla to pheromone puffs, and responses were observed consistently across various leg pairs. The researchers concluded that spiders' olfactory systems rival the sensitivity seen in insects, highlighting their advanced chemical detection capabilities.

Broader Implications

The study explored 19 other spider species and confirmed the presence of wall-pore sensilla in most male spiders, suggesting that this trait evolved multiple times. However, it was noted that some primitive species lack these structures. Future research is expected to investigate how female spiders detect smells, the types of chemicals relevant to their behaviours, and the evolutionary aspects of olfaction in spiders.

This breakthrough provides a foundation for understanding the sophisticated sensory mechanisms that govern spider behaviour.