Spider bites and venoms

Spider venoms are a cocktail of many chemicals. Some are neurotoxins, which evolved to kill or immobilise arthropods like insects by attacking their nervous systems; others are cytotoxins which help break down the tissue so the spider can ingest a liquefied meal. Unfortunately, a few of these chemicals can be seriously toxic to people.

How does spider venom work in humans?

Venoms are chemicals of biological origin (i.e. made by an animal) used for the purpose of attack or defence. Venoms are made by specialised organs, such as modified salivary glands, and are delivered via specialised systems such grooved or hollow fangs. Most venoms consist of a complex mixture of chemical substances, including proteins, peptides, sugars and other substances. Venoms may affect many systems of the body. Common venom effects include paralysis, interference with blood clotting, breakdown of muscle, pain, breakdown of tissues and effects on the cardiorespiratory system (the heart and lungs).

There are basically two types of venom that have an effect on humans: neurotoxic and cytotoxic (or necrotic) venoms. Neurotoxic venoms work directly on the nervous system. The best known example is the venom of the Black Widow/Redback spiders (Latrodectus species). (necrotic) venoms cause damage to the tissues, such as blisters and lesions. A good example is the venom of the White-tailed Spider (Lampona species). Generally, neurotoxic venoms kill more quickly than cytotoxic venoms.

Toxins which attack nerves

The main effect of a neurotoxic venom is to block nerve impulses to the muscles, causing cramps and rigidity and also disrupting many of hte body's functions. It also overstimulates the production of the neurotransmitters, acetylcholine and norephinephrine, causing paralysis of the entire nervous system. The combined effect causes sudden and severe stress to the entire human body. In extreme cases, this can result in death due to respiratory or circulatory failure. Funnel-web Spider venom - known as atraxotoxin - acts directly upon the nervous system in this way.

Toxins which attack the tissue

Necrotic venoms cause skin blisters around the site of the bite, which may lead to ulcers and tissue death - necrosis. Bites from some wandering spiders, including the White-tailed Spider, Wolf Spiders and the Sac Spiders (Cheiracanthum species) can also cause necrosis, but severity varies from little to acute reactions. Scientists are still determining which species cause most problems, as many spiders involved in necrotic bites have been misidentified in the past.

Making antivenoms

Antivenoms for spider toxins are produced by injecting horses, goats or rabbits with the spiders' venom. This doesn't harm these animals because they are either given only small venom doses or they have a naturally mild reaction to the venom. Antibody molecules are produced as a result of the reaction of the animal's immune systems to the foreign venom molecules. These are used to make life-saving antivenoms for humans. Molecular research aimed at making synthetic antivenoms is in progress.

First aid - points to remember

Those at greatest risk, as with any toxin, are the very young or elderly and those with pre-existing cardiovascular disease.
Suspected funnel-web or mouse spider bites should always be treated as quickly as possible by applying a pressure bandage and immobilising the victim (do not cut the wound or apply a tight tourniquet).
Bandaging is not necessary for Redback Spider bites. Applying pressure worsens the pain that often comes with Redback bites.
The application of a cold pack may help if the bite is painful. For most spider bites, no other first aid is necessary.
Always seek medical attention for any suspected funnel-web, mouse or Redback Spider bite and for any other bite if symptoms develop or persist.
Catch the spider for positive identification if you can.

Pressure bandages and splints

Pressure bandages slow down the movement of venom into the bloodstream, which reduces the effect of the nerve toxins in the venom. Pressure bandages should only be used for funnel-web or mouse spider bites. When the spider bites someone, the venom is injected into the tissue under the skin. A pressure bandage slows down the movement of both tissue fluid and blood near the surface. This prevents the venom from rapidly reaching the bloodstream and is very effective treatment as long as the patient is kept still.

Wind the bandage firmly around the bitten arm or leg starting from the bite. The bandage should not be so tight that it restricts blood flow.
Wrap the entire limb, then apply a splint to prevent movement.
Keep the victim as still as possible.
Do not remove the bandage.
Seek medical attention as soon as possible.

Catching a spider

Quickly place an empty jar over the spider
Push a stiff piece of card under the jar to cover its mouth
Up-end the jar so that the spider falls to the bottom
Quickly remove the card and securely replace the jar's lid

Last Updated: 20 October 2009

3 comments

STAFF

Louise Kampen
11.06 AM, 24 June 2009

Thanks for your comment, it does sound like you have some interesting spiders. For more information you should contact the American Arachnological Society http://www.americanarachnology.org/ and hopefully they will be able to answer your questions.

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sosoftail
10.06 AM, 24 June 2009

Hi. I live in SC USA. Been seeing a LOT on unusual spiders. I killed a really big spider recently that at first thought it was a black widow but if it was it was the biggest I had ever seen. Instead of the red hour glass it had a jagged bright red slash across its back. Recently a friend was helping me clean off my carport. A lot of stuff out there was given to me by a church to use in a yard sale since I used to have a lot of them. They had an unsuccessful one and stored the stuff a long time on the porch of an abandoned house. I did not check it but just brought it all home & put on carport but I got sick & lost my shade tree as well so no more yard sales. When moving an old steam vac she said she saw the mother of all black widows crawl up into bottom of it. Now I know where all my black widows are coming from. She sat it out in yard away from house so it would not come out near my house. She raises a variety of exotic snakes & spiders so if she says its the mother of all black widows I believe her. She said she removed 3 egg sacs but spider up inside vacuum. I still wonder about the giant widow with the red back. The shade tree I lost was about a 100 year old oak. It was hollow & weight of leaves made it split. When removing the tree & stump the tree guy had myself & my neighbors come see a giant spider that came out of the trunk. He called it a "mutant". Looked somewhat like what I call grass spiders but was the size of a small dog! He killed it thinking it was poisonous before I could get a picture of it. What is going on with spiders growing to unusual sizes around here? Plus the weird ones. I have even seen some pure white or bright orange all over. Yeah....I need an exterminator but we are in sort of a monsoon year and they won't do anything until rain stops. Could the big black widow be caught & sent to a place that makes anti-venom? Thanks a lot. CC

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