Scientists studying spiders and scorpions at the Zoological Collections Laboratory Butantan Institute in São Paulo, Brazil noticed something unusual about a spider just a few millimeters long. The animal appeared to be wearing a delicate pearl necklace. Unsure of what they were seeing, the team turned to a colleague who specializes in mites for answers.
Ricardo Bassini-Silva, researcher and curator of the laboratory’s acarological collection, quickly recognized that the bead-like structure was actually mite larvae. So far, Brazil has only had one documented case of mites that parasitize spiders, and this species belonged to a completely different family.
A new parasitic mite has been identified
A detailed analysis of the spider and its little passengers followed. Using light microscopy, scanning techniques and other morphological examinations, the scientists confirmed that they were looking at a new species. The find represents the second mite-parasitic spider ever described in Brazil and the first of its family recorded in the country.
The research was supported by FAPESP and published in the International Journal of Acarology. It combined two projects financed by FAPESP. One is led by Bassini-Silva, while the other is coordinated by Fernando de Castro Jacinavicius, study co-author and professor at the Institute of Biology at the University of São Paulo (IB-USP).
Rare genus map expansion
The newly identified species, named Araneothrombium brasiliensis, belongs to a genus first described in Costa Rica in 2017. The find in Brazil suggests that the group may be more widespread than previously thought and could exist in other Neotropical regions.
Each mite larva measures about 500 micrometers, or half a millimeter. The spiders they parasitize are only a few millimeters long. So far, scientists have only identified the larval stage of the mite. These larvae were found attached to juvenile spiders from three different families. All specimens collected were satiated, indicating that they had fed enough to significantly increase their size.
“For this group of mites, it is not unusual to know many parasitic species only through their larvae, because as adults they become free-living predators that live in the soil and feed on small insects and even other mites, making them very difficult to find,” says Bassini-Silva.
Where Parasitized Spiders Were Found
Spiders carrying the newly described mites were collected in Pinheiral, a municipality in the state of Rio de Janeiro. This area is near caves and grottoes, an environment similar to where the first known Brazilian species of spider mite, Charletonia pietrai, was discovered.
In a separate study published in 2022, scientists revisited an earlier species that was originally described in 1979. The updated work added new details about its physical characteristics, biology, geographic distribution, and host organisms, including spiders.
Why do mites target a spider’s weak spot?
Parasitic spider mites feed on lymph, a fluid that circulates through the body of certain arthropods. They draw this fluid through the pedicel, the narrow area connecting the cephalothorax (where the spider’s eyes and mouth are located) to the abdomen.
“This is the most vulnerable area of the spider, because other parts have a lot of chitin, which forms an exoskeleton that is difficult for the mite’s fangs to penetrate,” explains the researcher.
The tendency of mites to prey on immature spiders suggests opportunistic behavior, as younger spiders are more exposed to parasites and predators. The researchers also note that this species may not be limited to spiders. It could potentially parasitize other arthropods, including insects. This broader behavior has already been observed in Charletonia pietrai, which feeds on at least two different orders of insects.
Hidden biodiversity in museum collections
“With more than 3,000 species of spiders, Brazil has enormous potential for discovering new parasitic mites,” says Bassini-Silva.
The discovery also highlights the value of zoological collections for biodiversity research. The spiders examined in this study had been stored for years and the mites had gone unnoticed until now. According to Bassini-Silva, collaboration with field researchers and environmental consulting companies may soon lead to additional samples. He hopes these efforts will lead to the identification and description of other temperate species associated with a wide range of animals.
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