Most spiders are non-venomous and most spider bites are harmless. They may cause some local redness and pain, but can usually be managed at home by washing, applying ice and keeping the area clean.
But poisonous spiders thrive in many temperate areas of the United States, and knowing how to identify them and treat venomous spider bites is essential, said Suparna Kumar, M.D., a certified specialist in poison information at the Tennessee Poison Control Center at Vanderbilt University Medical Center.
"The two venomous spiders common to this area are the black widow and the brown recluse, and we have calls every year from people bitten by both of them," Kumar said.
In 2014, the Tennessee Poison Center received almost 300 calls regarding spider bites. More than half of these were about brown recluse spiders, and 40 calls were about black widow spiders.
"Most patients bitten by these two spiders experience only minor local effects," Kumar said. "A very small percentage of patients, particularly the very young or the elderly, may be at risk for a severe reaction to a venomous spider bite."
Brown recluse spiders are native to Southern and Midwestern states. They are medium sized, may be light yellowish brown to dark brown in color, and are distinguished by the characteristic violin shaped mark on the back.
They seek out dark, warm, dry environments such as attics, closets, porches, barns, basements, woodpiles and old tires.
"The bite of a brown recluse may cause mild stinging or pain, and could worsen becoming painful and itchy in the next two-to-eight hours," Kumar said. "The bite site may be itchy and red, and is often followed by the development of an extremely painful area which is usually blue or purplish in color, surrounded by grayish ring, which is in turn surrounded by a red outer ring—a typical 'bulls eye' pattern."
Kumar said the recommended home treatment for a brown recluse bite is to wash the area with soap and water, apply ice, and get a tetanus booster if necessary. "The bites usually heal very well if they are kept dry and clean and left alone," she said.
But some people develop systemic reactions to a brown recluse bite. Twenty-four to 72 hours after a bite, the patient may develop a fever, rash and muscle pain, and the toxin from the bite may be causing hemolysis, or destruction of blood cells.
"If systemic symptoms are noted, the patient will need to have his or her urine tested for the presence of hemoglobin or blood. If the urine test is positive for blood and/or the patient has signs of rash and fever, the patient should be admitted and observed for hemolysis," Kumar said. "This is especially important in children under 12 years of age, as toxin induced hemolysis can occur very rapidly."
The Black widow spider is glossy black in color, and identifiable by a reddish or orange colored hourglass marking on the abdomen. They are usually found in dark areas such as crawl spaces, inside boxes, water meter compartments and piles of firewood.
"People who are bitten by a black widow may not even realize it at first," Kumar said. "The bite feels like a pinprick, and often there is minimal local reaction—maybe a little bit of pain or redness at the site, which usually goes away quickly."
If those effects are all that occur, the bite can be managed by washing the area with soap and water, applying ice, and, if needed, getting a tetanus booster.
However, some black widow bites have much more severe systemic effects. These effects may start two to four hours after the bite, and can include headache, nausea, vomiting, changes in heart rate and blood pressure, painful muscle cramping, muscle twitching in the affected extremity, and even board-like rigidity.
"If any of these symptoms are noted, the patient will need to be monitored at a hospital, and treated with muscle relaxers, narcotics or benzodiazepines," Kumar said.
Fortunately, most spider bite patients recovers completely, but knowing how to avoid and treat such bites is critical, especially in those who encounter attics, crawlspaces and other areas where spiders live.
Vanderbilt University Medical Center