Spider bites

It is inevitable that spiders come in close contact with man from time to time but they are generally shy and very rarely bite human beings. When they are accidentally touched or squeezed, they might deliver a bite in self-defense. However, the fangs of small spiders are unable to pierce the skin and therefore don’t do any harm. In most cases we don’t even know if the venom of a specific spider will be able to hurt humans, just simply because we’ve never been bitten by any of them.

All spiders (except one family, Uloboridae) produce either cytotoxic or neurotoxic venom that they use to kill their prey.

Cytotoxic venom

This type of venom destroys the tissue around the bite and causes considerable tissue damage; lesions of up to 10 cm in diameter may develop. The symptoms develop gradually and often the person is unaware that he or she has been bitten until the area around the bite becomes painful.

Non-web dwelling spiders generally have cytotoxic venom and this type of venom may cause serious harm when delivered by sac spiders, violin spiders and sand spiders.

Neurotoxic venom

This type of venom affects the central nerve system and the bite is usually accompanied by severe pain. Web-dwelling spiders usually have this type of venom that may cause serious harm in humans when delivered by button spiders (also known as widow spiders).

Venom’s effect on humans

Very few spiders are potentially harmful to man. The signs and symptoms from a bite from a spider with neurotoxic venom would differ from those produced by a spider with cytotoxic venom. Also, the action of the venom may be influenced by the following factors:

• • The size of the spider and the amount of venom injected. In most cases only a single drop enters the person’s skin

• • The part of the body where a person is bitten. A bite near the head is more dangerous than for example one on a leg or arm

• • The age and health of the person. The bodies of young children and ill persons may be less able to cope with bites

• • The sensitivity of an individual to the venom. Just as some people are more sensitive or allergic to bee stings, the same goes for spiders

• • The species of spider that bit the person and therefore the type of venom (it helps if the spider can be identified so that the correct treatment can be given).

Symptoms

The bite and the site of the bite may be painless initially and symptoms may only develop later (1 to 8 hours after the bite), depending on the factors listed above. The symptoms may include the following:

• • Pain in the chest and abdomen

• • Breathing difficulties

• • Heart palpitations

• • Nausea and vomiting

• • Sweating and fever

• • Excessive saliva

• • Increased blood pressure

• • Rash

• • Swollen area around the bite.

What to do when bitten by a spider

When bitten by a spider, the most important thing is to try and identify the spider so that the right treatment can be given. In addition:

• • Wash the area well with soap and water

• • Place a cold soft cloth or an ice pack wrapped in cloth to the site

• • Take paracetamol pain medication

• • If symptoms occur, get medical attention or, if bitten by a violin, button, sac or sand spider, see a doctor as soon as possible.

Are spiders dangerous?

Only the bites of violin, button, sac and sand spiders are considered harmful in South Africa. Unfortunately myths and legends about the dangers of spider bites abound, exaggerating the dangers. In reality very few are dangerous.

You are advised, however, to wear gloves and tuck pants into socks when you are working in woodpiles, compost dumps, sheds and gardens to prevent spider bites.

 

Sources

 

Healthwise Handbook, 1998. Healthwise Inc, Boise, Idaho
http://goafrica.about.com
http://www.arc.agric.za
http://www.phuthu.co.za
http://www.spiderclub.co.za
http://www.tandfonline.com