Most spiders have venom, but few pose a threat to humans. Venom can be neurotoxic or cytotoxic. The black widow has neurotoxic venom, while the brown recluse has cytotoxic venom. Antivenom is available for some spider bites, but not all. Most spider bites are harmless, but those with compromised systems are at higher risk. If experiencing symptoms, seek medical help and bring the spider if possible.
Most spider bites are harmless, although all spiders except the Uloboridae family have venom. However, due to the varying potency of this poison, of the thousands of species in the world, relatively few pose a threat to humans.
Venom, whether it is spider or snake venom, 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 a very noticeable wound at the site of the bite itself. By blocking impulses to the muscles, the neurotoxic venom causes cramping, stiffness and has a general numbing effect. This venom kills faster than cytotoxic venom 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 venom is necrotic venom, from the word necrosis, which refers to the breakdown of cells and tissues. The bite of a spider with cytotoxic venom will cause a bruise similar to a mosquito bite and a noticeable wound. There will be necrosis and the wound 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 best known and very poisonous spiders you will find:
The Australian funnel spider (species atrax and hadronyche)
Redback, katipo or black widow spiders (species latrodectus)
South American banana or Brazilian wandering spiders (phoneutria
specie)
Brown recluse spiders (species loxosceles)
Hobo spiders (especially wild spiders)
Antivenom is available for funnel spider, redback, black widow, and South American banana bites. There is no antivenom for brown recluse 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) is considered harmless.
It is safe to estimate that hundreds of thousands of people are bitten by spiders each year with no ill effects. Even a bite from a spider listed above may produce no symptoms. The spider may not inject 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 bruise that resembles a mosquito bite and will disappear within 24 hours. However, children, the elderly, or people with compromised systems are at a higher risk of serious reactions. Allergic reactions can also cause problems with spider bites that aren’t normally considered dangerous.
If you believe you’ve been bitten by a spider and are experiencing symptoms that concern you, contact your doctor or your local poison control center. If possible, take the spider safely with you when you seek medical help. Many spider bites share common symptoms and can be misdiagnosed without the spider. Dead or crushed spiders can still be evaluated for diagnostic purposes.
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