Here is Part Two of Dr. Jorge Parada’s, a medical spokesperson for the National Pest Management Association (NPMA), excellent article on spider bites that was featured in PestWorld news.
The two spiders of greatest concern in the United States are the brown recluse and the black widow spiders, most commonly found in southern states. Both species prefer warm climates and dark, dry places. Typically, these are timid, non-aggressive spiders, often found in dry, littered, undisturbed areas such as closets, woodpiles and under sinks.
Black Widow Spiders. Black widow spiders can be found throughout North America, but are most common in the southern and western areas of the United States. Male widows, like most spider species, are much smaller and generally less dangerous than the females. Widows tend to be non-aggressive, but will bite if the web is disturbed and the spider feels threatened. The more dangerous female is a dark colored spider and with a red hourglass marking on its belly. The bite feels like a pinprick, and at first may go unnoticed or seem rather minor. Early on there may be slight swelling and faint red marks. Within a few hours, though, intense pain and stiffness begin. Other signs and symptoms include: chills, fever, muscle cramps, and gastrointestinal symptoms such as nausea, vomiting and severe abdominal pain. Typically, black widow bites are less common, but more severe than brown recluse bites. That said, no one in the United States has died from a black widow spider bite in more than 10 years.
Brown Recluse Spiders. The brown recluse spider, also known as the violin spider, is most commonly found in the south-central, mid-western and southern states of the United States. Most encounters with this spider occur from moving boxes or rooting about in closets, attics, garages or under beds where they may have nested. These spiders are brown in color with a characteristic dark violin-shaped (or fiddle-shaped) marking on its head. Whereas most spiders have eight eyes, brown recluses have six equal-sized eyes. The bite produces a mild stinging, followed by local redness and intense pain within eight hours. A fluid-filled blister forms at the site and then sloughs off to leave a deep, enlarging ulcer. Systemic (or generalized) reactions from a brown recluse spider bite vary from a mild fever and rash to nausea and listlessness. Generally, brown recluse spider bites are reported much more frequently than black widow bites, but while the brown recluse bite may cause very significant local skin reactions, it is much more unusual for these bites to cause generalized symptoms. Unfortunately, brown recluses are almost communal and can be sometimes be found in great numbers.