Second spider-parasitic mite described in Brazil

The parasitic mites were found on juvenile arachnids in the Butantan Institute collection. The larvae of Araneothrombium brasiliensis were collected in Rio de Janeiro. Previously, the genus had only one known species in Costa Rica.

By André Julião  |  Agência FAPESP – When researchers studying spiders and scorpions at the Zoological Collections Laboratory of the Butantan Institute in São Paulo, Brazil, came across a few-millimeter-long spider wearing something resembling a pearl necklace, they knocked on the door of a colleague specializing in mites.

Ricardo Bassini-Silva, a researcher and curator of the Acarological Collection at the same laboratory, quickly identified the “necklace” as mite larvae. Previously, there had only been one record of spider-parasitic mites in Brazil, and even then, they were from a different family.

Examining the animal’s morphological characteristics using microscopy, scanning, and light techniques resulted in the description of the second spider-parasitic mite in Brazil and the first of its family in the country. 

Supported by FAPESP, the study was published in the International Journal of Acarology.

The study integrates two projects supported by FAPESP. One is coordinated by Bassini-Silva, and the other is coordinated by Fernando de Castro Jacinavicius, co-author of the article and a professor at the Institute of Biology at the University of São Paulo (IB-USP).

The spider, named Araneothrombium brasiliensis, belongs to a genus that was first described in Costa Rica in 2017. Its discovery in Brazil suggests that the genus may be present in other neotropical countries. 

The individuals are about 500 micrometers, or half a millimeter, in size. The parasitized spiders are a few millimeters long. Currently, only the larvae are known; they were found parasitizing three families of juvenile spiders. All specimens were engorged, meaning they had fed to the point of greatly increasing their size.

“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,” says Bassini-Silva.

The spiders parasitized by the new species of mites were collected in Pinheiral, a municipality in the state of Rio de Janeiro. The environment was close to caves and grottos, similar to that of the first Brazilian species of spider-parasitic mite, Charletonia rocciai.

In a paper published in 2022, the researchers redescribed the species first described in 1979. They added new morphological characteristics, biological data, locations of occurrence, and hosts, including spiders. 

Dorsal and ventral overview of the new species. Brazil has the potential to discover new parasitic mites (photo: Ricardo Bassini-Silva)

Pearl necklace

Spider mites feed on lymph, a fluid that circulates through the bodies of certain arthropods. They suck the fluid through the pedicel, which is the region between the cephalothorax (where the spider’s eyes and mouth are located) and the abdomen. 

“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,” the researcher explains. 

Their presence on juvenile spiders may indicate opportunistic behavior, as young individuals are more vulnerable to parasites and predators. Additionally, the species could potentially parasitize other arthropods, such as insects. This is the case with Charletonia rocciai, which parasitizes at least two orders of insects.

“With more than 3,000 species of spiders alone, Brazil has immense potential for discovering new parasitic mites,” says Bassini-Silva.

The study also highlights the importance of zoological collections in studying biodiversity. The spiders had been stored for years, and no one had noticed the mites until now. 

Through partnerships with researchers and environmental consulting companies that work in the field, Bassini-Silva hopes to soon receive more mites associated with other animals and describe new species.

The article “First species description of Araneothrombium Mąkol, Felska and Król, 2017 (Trombidiformes: Microtrombidiidae) parasitizing spiders in Brazil” can be read at www.tandfonline.com/doi/full/10.1080/01647954.2025.2566344.