Recognizable by their brown bodies, long legs, and self-burying behavior, spiders of the genus Sicarius formed isolated populations at least 15 million years ago in open and sun-scorched areas of Brazil and other South American countries, according to a survey by biologists from the Butantan Institute, the Federal University of Minas Gerais (UFMG), and the Bernardino Rivadavia Natural Sciences Argentine Museum (MACN).
With a leg span of up to 12 centimeters, Sicarius produces a venom that is chemically very similar to that of the Loxosceles, or recluse spider. The also six-eyed, but smaller, Loxosceles is feared for its potential to cause injury to humans—around 2,000 Loxosceles bites are reported each year in the metropolitan area of Curitiba, Paraná, where bite incidence is highest in Brazil. In 2013, another team from Butantan reported that spiders of both genera produce venom containing the enzyme Sphingomyelinase-D, a protein that causes tissue destruction at the bite site. The only documented report of a Sicarius bite in Brazil was in 1992, involving a 17-year-old boy.
Sicarius appears not to pose a risk because it lives in a different habitat, explains biologist Antonio Brescovit, the Butantan researcher who coordinated the survey. “Sicarius have a very limited range and live in desert areas that are usually far from houses and people,” he says. “Loxosceles, on the other hand, typically move around a lot. They make their way into people’s houses and crawl into their clothes and shoes, but will only bite and release their venom if they inadvertently become trapped against the skin.”
The researchers covered about 50,000 kilometers and collected spiders in 150 locations in Brazil, Chile, Peru, and Argentina. The survey, which is described in detail in an article published in April 2017 in the Zoological Journal of the Linnean Society, has expanded the total number of known species of the genus from 15 to 21 in the Americas and from one to six in the Northeast of Brazil.
The only species known to occur in Brazil’s Caatinga prior to the survey, Sicarius tropicus was collected at four locations. However, the biologists found that while two specimens were indeed S. tropicus, the other two were of a separate species, which they named S. cariri. They also identified another four new species (see map). “Sicarius diadorim and jequitinhonha are so similar that we could only tell them apart after comparing their DNA sequences,” says biologist Ivan Magalhães, a researcher from UFMG.
Systematics of neotropical haplogyne spiders (Arachnida, Araneae) (No. 11/50689-0); Grant Mechanism Thematic Project; Principal Investigator Antonio Domingos Brescovit (Instituto Butantan); Investment R$1,200,792.13.
MAGALHÃES, I. L. F. et al. Phylogeny of Sicariidae spiders (Araneae: Haplogynae), with a monograph on Neotropical Sicarius. Zoological Journal of the Linnean Society, Vol. 179 (4), pp. 767–864. 2017.