Envenomation from Spider or Animal Bites

First aid for venomous bites and stings

1. Move away from the animal. Do not try to catch or kill it. A photo from a safe distance can help identification.
2. Call 911 for snakebites or severe symptoms. For other bites, call Poison Help at 1-800-222-1222 (US) for expert advice.
3. Keep the person calm and still. Movement spreads venom faster.
4. Remove rings, watches and tight clothing near the bite before swelling starts.
5. Keep a bitten limb at about heart level and loosely immobilized with a splint or sling.
6. Mark the edge of swelling with a pen and note the time, so progression can be tracked.
7. Clean the wound gently with soap and water for spider bites and stings.
8. For marine stings such as stingrays or venomous fish, immerse in water as hot as can be tolerated (not scalding) for 30 to 90 minutes to ease pain.

Do not:

• cut the wound or try to suck out venom
• apply a tourniquet or tight band
• apply ice to snakebites or immerse them in ice water
• use electric shock
• give alcohol or caffeine
• delay getting to a hospital to try home remedies

Venomous animals in the US

Pit vipers

Rattlesnakes, copperheads and cottonmouths (water moccasins) cause most venomous snakebites in the US. Their venom damages tissue and blood vessels and interferes with clotting.

• immediate burning pain, swelling spreading up the limb, bruising and blistering
• nausea, vomiting, sweating, metallic taste, tingling around the mouth
• low blood platelets and clotting problems, which may cause bleeding
• in severe cases, low blood pressure and shock

About a quarter of pit viper bites are "dry," with no venom injected, but this cannot be judged at the scene.

Coral snakes

Found in the southern US, with red, yellow and black bands. Bites may cause little pain or swelling, but the neurotoxic venom can cause drooping eyelids, slurred speech, difficulty swallowing and breathing paralysis, sometimes 12 hours or more later. Anyone bitten needs hospital observation.

Black widow spiders

Shiny black spiders with a red hourglass marking on the belly. The bite may feel like a pinprick, then within an hour cause:

• spreading muscle cramps and pain, especially in the belly, back and chest
• a rigid belly that can mimic appendicitis
• sweating, high blood pressure, fast heart rate, nausea and restlessness

Symptoms peak at 1 to 6 hours and can last days. Deaths are very rare with modern care.

Brown recluse spiders

Found mainly in the South and Midwest, with a violin-shaped mark on the back. Most bites cause only a red bump. Some develop a painful, blistering lesion with a dark center that can break down into an ulcer over days to weeks. Rarely, especially in children, the venom causes fever, rash and breakdown of red blood cells. Many skin wounds blamed on recluse spiders are actually MRSA infections, particularly in areas where recluses do not live.

Scorpions

Most US scorpion stings cause local pain only. The Arizona bark scorpion, found in the Southwest, can cause neurotoxic effects, particularly in young children: restlessness, roving eye movements, drooling, muscle jerking, difficulty swallowing and breathing problems.

Others

• Gila monsters: painful bites with swelling. Rarely serious.
• Marine animals: jellyfish, stingrays, lionfish and stonefish cause intense pain. Some jellyfish species are dangerous.
• Bees, wasps and fire ants: usually cause local reactions, but can cause anaphylaxis in allergic people or toxic reactions after hundreds of stings. See insect bites.

Hospital assessment

• Examination and repeated measurement of swelling every 15 to 30 minutes for snakebites
• Blood tests: blood count, platelets, clotting tests (PT/INR, fibrinogen), kidney function and creatine kinase, often repeated
• Observation: at least 8 hours for pit viper bites without symptoms, and at least 12 to 24 hours for coral snake bites
• ECG and vital sign monitoring

Treatment

Antivenom

Antivenom neutralizes venom and is the key treatment for significant envenomation.

• Pit vipers: CroFab or Anavip, given for progressive swelling, abnormal blood tests or systemic symptoms. Further doses may be needed.
• Coral snakes: North American coral snake antivenom, often given early, before symptoms, because paralysis can be hard to reverse.
• Bark scorpions: Anascorp, for significant neurotoxic symptoms.
• Black widow: antivenom exists but is reserved for severe cases because of allergic reaction risk.

Supportive care

• pain relief, including opioids for black widow cramps
• benzodiazepines for muscle spasms and agitation
• wound care, tetanus vaccination if not up to date
• antibiotics only if infection develops
• surgery is rarely needed. Compartment syndrome is uncommon after snakebite and is usually treated with antivenom first

Brown recluse wounds

Clean wound care, cool compresses, elevation and pain relief. Most heal over weeks without surgery. Early surgical removal is not recommended. Watch for cellulitis or other wound infection.

Prevention

• wear boots and long pants in snake country, and watch where you put your hands and feet
• use a flashlight at night on trails
• leave snakes alone. Many bites happen when people try to handle or kill them
• shake out shoes, gloves and clothing in areas with spiders or scorpions
• reduce clutter in garages and sheds, seal cracks, and move beds away from walls in scorpion areas
• wear gloves when moving wood or boxes

Frequently asked questions

What is envenomation?

Envenomation is poisoning by venom injected through a bite or sting from an animal such as a snake, spider, scorpion, bee, jellyfish or venomous fish. Effects range from local pain and swelling to bleeding problems, muscle cramps, paralysis and, rarely, death.

What should you do if bitten by a venomous snake?

Call 911, move away from the snake, keep calm and still, remove rings and watches, keep the limb at heart level, and mark the swelling edge. Do not cut, suck, apply a tourniquet or ice. Get to a hospital, where antivenom can be given if needed.

What are the symptoms of a black widow spider bite?

A black widow bite may feel like a pinprick, followed within an hour by spreading painful muscle cramps, especially in the belly, back and chest. Sweating, nausea, restlessness, high blood pressure and a fast heartbeat are common. Seek medical care.

How do you know if a spider bite is serious?

Seek care if you develop spreading cramps or belly rigidity, a darkening or blistering wound, spreading redness, fever, or feel unwell. Most spider bites cause only mild redness and itching and heal with simple care. Many suspected spider bites are actually skin infections.

Is antivenom always needed for a snakebite?

No. Some bites are dry, with no venom injected, and some cause only mild local effects. Doctors observe patients and give antivenom if swelling spreads, blood tests become abnormal or systemic symptoms appear. Coral snake bites are often treated earlier.