Just 175 of 47,000 spider species can put human health at risk

    13 de marzo de 2018

    Mexico City, Mar 13 (efe-epa).- Fear of spiders comes from the threat people think they pose to human life and health, though of the more than 47,000 known species, only 174 could be dangerous, Mexican arachnid specialist Diego Barrales Alcala told EFE.

    The World Health Organization (WHO) considers just 175 species in four genera of spiders to be a threat, according to the researcher at the Biology Institute of the National Autonomous University of Mexico (UNAM)

    These genera are the Atrax (funnel-web spiders), indigenous to Australia; Loxosceles (recluse spider), found in Mexico; Latrodectus (black widow), abundant in North America; and Phoneutria (wandering spider), with a habitat from Costa Rica to Brazil.

    He said that Mexico has a great variety of spiders, more than 5,000 species, and among those commonly seen are various species of scorpion, tarantulas and daddy long-legs, while some others are hard to observe because of their size or habitats.

    Many spiders are nocturnal, they avoid the light and hide in vegetation, under rocks, in holes in the ground or in the walls of people's houses, he said.

    The book "Biological Capital of Mexico" lists 127 species of spiders in Mexico City, of which just two are considered dangerous: the black widow and the recluse spider.

    About the recluse spider, he said it lives in hot climates and it is unknown how it came to Mexico City: "There's no way to know if it was indigenous or came as an invasive species."

    Spiders travel on products brought from the countryside, like food items, plants, timber and even in people's suitcases.

    The recluse spider is identified by its light brown color, a slightly lengthened tail, while on it head is a mark shaped like a violin, so that it is sometimes called the violin spider.

    Its bite causes no immediate pain and the symptoms appear between six and 12 hours afterwards in an infected spot that can necrotize, or kill, the surrounding skin tissue.

    The black widow, for its part, has a red mark on its black body and its poison attacks the nervous system. Its bite is painful and causes symptoms of sweating, nausea, difficulty in breathing and cramps.

    In both cases, Barrales Alcala recommended seeing a doctor and was sorry that spiders cause people such phobias that they'd often rather kill them before identifying them.

    If we eradicate spiders, it could cause untold harm to our ecosystems, the specialist said.