In the US there are 3 main spiders that are considered “Dangerous”. These 3 spiders are the Black Widow, Brown Recluse and the Brown Widow. Here is some information on all of them.
At least five species of recluse spiders are found in the United States. The brown recluse spider (Loxosceles reclusa) is the best known and found most commonly in the South and southern Midwest. However, interstate commerce has created habitats in many other parts of the country for the brown recluse and related species. The spider is brown, with an average body length of just under 1/2 inch. A characteristic dark violin-shaped marking (“fiddleback”) is found on the top of the upper section of the body. The brown recluse spider is found in dark, sheltered areas, such as under porches, in woodpiles, and in crates of fruit. It is most active at night. It commonly bites when it is trapped, but is not otherwise aggressive toward humans.
The bite of the brown recluse spider may cause very little pain at first, or a sharp sting may be felt. The stinging subsides over 6 to 8 hours, and is replaced by aching and itching. Within 1 to 5 hours, a painful red or purplish blister sometimes appears, surrounded by a bull’s-eye of whitish-blue (pale) discoloration, with occasional slight swelling. The red margin may spread into an irregular fried-egg pattern, with gravitational influence, such that the original blister remains near the uppermost part of the lesion. The victim may develop chills, fever, weakness, and a generalized red skin rash. Severe allergic reactions within 30 minutes of the bite occur infrequently. Over 5 to 7 days, the venom causes a violet discoloration and breakdown of the surrounding tissue, leading to an open ulcer that may take months to heal. If the reaction has been severe, the tissue in the center of the wound becomes destroyed, blackens, and dies.
Black widows are notorious spiders identified by the colored, hourglass-shaped mark on their abdomens. Several species answer to the name, and they are found in temperate regions around the world.
This spider’s bite is much feared because its venom is reported to be 15 times stronger than a rattlesnake’s. In humans, bites produce muscle aches, nausea, and a paralysis of the diaphragm that can make breathing difficult; however, contrary to popular belief, most people who are bitten suffer no serious damage—let alone death. But bites can be fatal—usually to small children, the elderly, or the infirm. Fortunately, fatalities are fairly rare; the spiders are nonaggressive and bite only in self-defense, such as when someone accidentally sits on them.
Unlike its starkly black-and-red colored relative, the black widow, the coloration of a brown widow consists of a mottling of tan and brown with black accent marking. In mature females, there is usually a dorsal longitudinal abdominal stripe and three diagonal stripes on each flank. At the top of each diagonal stripe, there is a black mark, which is rather conspicuous and square-ish. The Brown Widow Spider does have an hourglass but it is typically an orange shade rather than the vivid red of a black widow. The brown widow looks similar to immatures of the western black widow spider, the latter of which has smaller black spots on the top of the diagonal abdominal stripes and more olive grey background coloration. Being able to discern brown widows from immature black widows is therefore difficult and requires some experience. However, a more diagnostic feature of a brown widow is its egg sac. Most spider egg sacs that are free (i.e., are not attached to flat surfaces) look like a lemon drop candy or a little cotton ball with indistinct edges. The egg sac of a brown widow has multiple silk spicules projecting out from the surface. The egg sac has been described as looking like a large pollen grain or a World War II harbor mine designed to blow up ships. The egg sac of the Brown Widow Spider is so distinctive that it is readily recognizable.
The bite of a brown widow spider is minor in comparison to that of a black widow. Although one frequently cited study demonstrates that, drop per drop, brown widow spider venom is as toxic as other widow species, venom toxicity is only one aspect when considering a spider’s bite potential. An African study with 15 verified bites demonstrated that the brown widow spider bite victims showed none of the classic symptoms of latrodectism, a response induced by neurotoxins in the venom of spiders in the genus Latrodectus (e.g., brown widows, black widows [L. mactans], Australian redbacks [L. hasselti], European black widow [L. tredecimguttatus], and New Zealand’s katipo spider [L. katipo]). The reason for the weaker effect of brown widow bites on humans is possibly because the brown widow does not have or cannot inject as much venom as its larger relatives. The two major symptoms of a brown widow bite were that the bite hurt when it was inflicted and it left a red mark. These two symptoms are not much different from the bite of normal household spiders. However, there is one recent report of a verified brown widow bite manifesting in more severe symptoms that required hospitalization of the bite victim.
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