Most spider bites cause minor swelling, inflammation, and itching. However, bites from poisonous spiders can cause more severe reactions.
Black widow bites affect the nervous system. The bite from a black widow may go unnoticed or may feel like a pinprick. Two small, red spots show where the fangs pierced the skin. Some people will not suffer any ill effects. However, others may suffer severe pain and cramps that spread from the site of the bite to the large muscles of the arms, legs, and abdomen. This usually occurs in 30 to 60 minutes after the bite.
The toxin can also cause salivation, high blood pressure, constriction of blood vessels, fast heart rate, pain, numbness, tingling, headache, anxiety, sweating, nausea, and vomiting, among other symptoms. The venom can cause whole-body reactions and can even be fatal, especially in very young and old people.
Brown recluse spider bites affect the skin and surrounding tissue. The bite of a brown recluse spider is often painless, but it may sting. Within a few hours, it becomes painful and itchy. The bite area is first surrounded by a bluish-white ring. In most people, the bite will heal in 2 to 3 days. However, in others, the toxin will cause swelling, tissue death, and destruction of red blood cells. A scab will form over the site and may leave a scar. The venom may also affect the eyes, causing swelling or drooping of the eyelid and other effects.
The toxin can also cause other symptoms within 72 hours of the bite including fever, chills, nausea, vomiting, headache, and weakness. Bites can cause whole-body reactions and can even be fatal. Rare complications of brown recluse spider bites include kidney failure and hemolytic anemia, which is anemia due to the destruction of red blood cells.
Tarantula hairs contain a toxin that can cause a serious skin rash, an allergic reaction, and possibly even anaphylactic shock. A threatened tarantula spider will eject up to thousands of small hairs from its hind legs that can pierce human skin. This produces itchy bumps on the skin that can last for weeks. People should wear gloves or wash their hands after handling pet tarantulas because the hairs are easily transferred to the eyes and can cause very serious effects. Tarantulas rarely bite – the bites are usually harmless but occasionally cause pain and swelling.