[Animals] 9 of the World’s Deadliest Spiders

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More than 43,000 different species of spiders are found in the world. Of these, only a small number are said to be dangerous, and less than 30 (less than one-tenth of one percent) have been responsible for human deaths. Why are so few spiders harmful to humans? Much of the reason may result from the size differences between people and spiders. Spider venom is designed to work on smaller animals, but the venom of some species can produce skin lesions in people or produce allergic reactions that result in fatalities. It is important to understand, however, that “death by spider bite” is very rare since clinics, poison control centers, and hospitals often have various species-specific antivenin (the antitoxin) on hand to treat the bite.

The brown recluse spider is one of the most dangerous spiders in the United States. Its venom destroys the walls of blood vessels near the site of the bite, sometimes causing a large skin ulcer. Research in 2013 revealed that a protein in the spider’s venom targets phospholipid molecules, which make up a good portion of cell membranes, and transforms these molecules into simpler lipids. The wound that is produced may require several months to heal, or it may become infected, which could lead to the death of the victim. Deaths from brown recluse spider bites are rare.
Most brown recluse spiders, which are also called violin spiders, live in the western and southern United States. Most are about 7 mm (0.25 inch) and have a leg span of about 2.5 cm (1 inch). On the front half of its body (the cephalothorax), it has a dark violin-shaped design, the “neck” of which is formed by a conspicuous furrow on the midline of its back. The brown recluse has extended its range into parts of the northern United States, making its home in caves, rodent burrows, and other protected environments. Brown recluse spiders also set up shop in the undisturbed spaces of buildings, such as attics, storage areas, and wall or ceiling voids.

https://www.britannica.com/list/9-of-the-worlds-deadliest-spiders