Most spider bites are not dangerous, although all spiders, with the exception of the family uloboridae They have poison. However, due to the variable potency of this poison, of the thousands of species in the world, relatively few pose a threat to humans.
Venom, whether spider or snake, can be classified into two types: neurotoxic or cytotoxic.
The black widow is an example of a spider with neurotoxic venom. This venom directly affects the nervous system, although there may not be much of a noticeable wound at the site of the sting. By blocking muscle impulses, the neurotoxic venom causes cramps, stiffness, and has a general paralyzing effect. This poison kills faster than the cytotoxic poison and is considered more potent. The Australian funnel-web spider is an example of a spider with neurotoxic venom.
Spiders like the brown recluse spider have cytotoxic venom. Cytotoxic poison is necrotic poison, from the word, necrosis, which refers to the breakdown of cells and tissues. A spider bite with cytotoxic venom will cause a mosquito bite-like welt and a noticeable wound. Necrosis will be present and the sore will be slow to heal and may require medical attention to prevent secondary infection. Spider bites of this nature can create severe flu-like symptoms, and in rare cases, can be fatal.
Among the most poisonous and highly poisonous spiders you will find:
- Australian funnel-web spider (atrax and hadronyche species)
- Red back spiders, katipo or black widow (Latrodectus species)
- South American banana or Brazilian wandering spiders (phonenutria species)
- brown recluse spiders (loxosceles species)
- hobo spiders (Tegenaria agrestis species)
Antivenin is available for funnel, redback, black widow, and South American banana spider bites. There is no antivenom for brown recluses or hobo spiders, but treatment in the form of antibiotics is commonly given to prevent secondary infection at wound sites.
The North American Banana Spider (argiope) it is considered harmless.
It is safe to estimate that hundreds of thousands of people each year are bitten by spiders with no ill effects. Even a bite from a spider mentioned above may not produce symptoms. The spider may inject no venom, or it may inject very little and the wound may heal on its own. In most cases, a spider bite will produce a local welt that resembles a mosquito bite and will go away within 24 hours. However, children, the elderly, or people with compromised systems are at higher risk for serious reactions. Allergic reactions can also cause problems with spider bites that are not normally considered dangerous.
If you think you have been bitten by a spider and are experiencing symptoms that concern you, contact your doctor or your local poison center. If possible, bring the spider safely when seeking medical attention. Many spider bites share common symptoms and can be misdiagnosed without the spider. Dead or crushed spiders can still be tested for diagnostic purposes.