🕷️ Where does this 'pearl necklace' discovered on a spider come from?

A fortuitous observation in the zoological collections of the Butantan Institute in Brazil proved particularly intriguing. While sorting spiders and scorpions, researchers noticed a small arachnid adorned with a structure reminiscent of a pearl necklace. This unusual discovery immediately raised questions about the nature of this appendage.

Upon closer examination, these 'pearls' turned out to be larvae of parasitic mites. Until then, Brazil had only one documented case of parasitic mites on spiders, involving a different family. This new find thus promises to expand our knowledge of the interactions between these small organisms.


To validate their discovery, the scientists used various microscopic techniques. Their morphological analyses led to the identification of a new species of parasitic mite, named Araneothrombium brasiliensis. This work, supported by FAPESP, was published in the International Journal of Acarology, marking a notable advance.

This mite belongs to a genus first described in Costa Rica in 2017. Its presence in Brazil indicates that related species could exist in other Neotropical countries. The larvae, measuring about 0.02 inches (0.5 mm), parasitize juvenile spiders only a few millimeters long (approximately 0.1-0.2 inches).

The specimens were collected near caves in Pinheiral, in the State of Rio de Janeiro, an environment comparable to that of another Brazilian species of spider-parasitic mite. The researchers observed that all the larvae were engorged with food, a sign that they had consumed a large amount of lymph.

These mites feed by sucking lymph at the pedicel, the most vulnerable region of the spider. This attack on young individuals could correspond to opportunistic behavior, as juveniles are more sensitive to parasites. Moreover, these mites could parasitize other arthropods, such as some insects.

With over 3000 species of spiders in Brazil, the potential for similar discoveries is immense. This study shows the interest of zoological collections, where specimens preserved for years can yield surprising elements. The researchers now wish to receive more mites to be able to describe new species.