Spiders smell with their legs. And we already know how

It was said that spiders smell, but why? A new study may have the answer — the key is in leg hair.

There is a lot of evidence that spiders can detect odors such as sex pheromones. But, without antennae, like other insects, what is their olfactory organ?

A new one published in Proceedings of the National Academy of Sciencesdemonstrated that male spiders use olfactory poles called wall-pore sensilla (“parietal pore sensilla”, literally translated) on your legs like a “nose” to detect sexual pheromones released by female spiders.

Investigators discovered sensilla of parietal pores, previously unknown, in legs of male wasp spiders (Argiope bruennichi) and we demonstrated that they can use them to detect airborne sex pheromones with high sensitivity, explains the study author Dan-Dan Zhang in an article.

The study looked at spiders A. bruennichi males and females through high resolution scanning electron microscopy. He discovered thousands of wall pore sensilla on all the legs of male spiders and revealed their specific characteristics.

A A. bruennichi is one of the few species of spiders in which the chemical structure of the sex pheromone has been effectively identified. Female spiders release gaseous pheromones that attract males from a distance.

The researchers then decided to test whether the sensilla in the pore wall responded to the pheromone compound. In these experiments, they mounted live male spiders under a microscope and placed a recording electrode at the base of a single pore-wall sensilla.

Each sensil was then exposed to a puff of pheromone. We discovered that even a small amount of the pheromone compound — barely 20 nanograms — was enough to elicit a clear response as a burst of activity in the neuronal cells of a wall pore sensillum, and the response became stronger as the dose increased.

In other words, spiders’ olfactory sensilla are incredibly sensitive, compared to those of other insects.

However, the sensilla are absent in groups of spiders that branch basally, like spiders Arbanitis sp.found in Asia. The pattern found suggests that wall pore sensilla evolved independently several times in spiders and were lost in some lineages.

This study paves the way for a deeper exploration of spider biology, and gives rise to new questions, to which scientists will have to seek answers. How did the sense of smell evolve in the vast diversity of spider species?