Scientists in Brazil have discovered a new species of parasitic mite that resembles a pearl necklace on tiny spiders. The mites, named Araneothrombium brasiliensis, attach to juvenile spiders and feed on their lymph fluid. This marks the first record of the mite's family in the country.
Researchers at the Butantan Institute in São Paulo, Brazil, stumbled upon an unusual sight while examining stored spider specimens: a tiny spider adorned with what appeared to be a delicate pearl necklace. Upon closer inspection, the "necklace" turned out to be clusters of mite larvae, leading to the identification of a new species.
The discovery was made by Ricardo Bassini-Silva, curator of the institute's Acarological Collection, who recognized the bead-like structures as parasitic mites. Detailed morphological analysis using light microscopy and scanning techniques confirmed the mites as Araneothrombium brasiliensis, belonging to a genus first described in Costa Rica in 2017. Each larva measures about 500 micrometers and was found engorged on juvenile spiders from three different families, all collected in Pinheiral, a municipality in Rio de Janeiro state near caves and grottos.
These mites feed on the spider's lymph fluid through the pedicel, the narrow connection between the cephalothorax and abdomen, which is the animal's most vulnerable spot due to its thin chitin layer. "This is the spider's most vulnerable region since other parts have a lot of chitin, which forms an exoskeleton difficult for the mites' fangs to penetrate," Bassini-Silva explained.
The finding represents only the second spider-parasitic mite described in Brazil and the first from the Microtrombidiidae family. Adult mites in this group are free-living predators in the soil, making them hard to find, while larvae parasitize hosts. "For this group of mites, it isn't uncommon to know many parasitic species only through their larvae, since in adulthood they become free-living predators, living in the soil and feeding on small insects and even other mites, which makes them very difficult to find," Bassini-Silva noted.
The research, supported by the São Paulo Research Foundation (FAPESP), was published in the International Journal of Acarology. It highlights the hidden biodiversity in museum collections, with the spiders having been stored for years before the mites were noticed. Brazil's over 3,000 spider species suggest potential for more discoveries, and the mites may also target other arthropods like insects.