Lesson Overview
Learning objectives
- Assess an animal bite and care for the wound in the right order
- Recognize and manage venomous snakebite, from pit vipers and from coral snakes
- Treat stings from bees, wasps, and their relatives (hymenoptera) and spider bites, and tell neurotoxic from cytotoxic presentations
- Remove a tick properly and recognize tick-borne illness
- Manage marine envenomation from jellyfish, stingrays, and sea urchins
Why this lesson matters
Most bites are minor. A few aren't, like a rattlesnake bite or a bat bite nobody noticed, and those need a hospital however the patient looks. Most of this lesson is about telling them apart.
Envenomation in the wilderness
North America's list of animals that can seriously hurt you is short. Leave them alone. Envenomation means an animal has injected venom into tissue, and what that venom does depends on the species. Hemotoxic venoms (pit vipers) destroy tissue around the bite and disrupt clotting. Neurotoxic venoms (coral snakes, some spiders) go after the nervous system. If you know what bit them, and which kind of venom you're dealing with, you know what to watch for, and the hospital will want that information. In the field, every snakebite gets the same care.
Animal Bite Assessment & Management
Wound assessment priorities
Work through an animal bite in this order.
- Depth: Did it go through the dermis? Are deeper structures (tendon, bone, vessel) involved?
- Mechanism: Crush, puncture, tear, or laceration? Each carries a different infection risk and heals differently.
- Contamination: Every animal bite is contaminated. Note the species, and whether the animal was provoked.
- Neurovascular status: Check CSM (Circulation, Sensation, Motion) beyond the bite. That means distal pulses and capillary refill, feeling, and movement. A serious bite may need an urgent check of the blood vessels at a hospital.
- Time elapsed: How long ago was the bite? It affects the infection risk and whether the wound can be closed later.
Wound care principles
Aggressive irrigation is the most important thing you can do for an animal bite. Use clean water or saline, and use a lot, at least 1-2 liters for a significant bite. Irrigation flushes out the bacteria and debris that would otherwise start an infection. Do not close a bite wound in the wilderness, with sutures or with adhesive strips. Leave it open to drain and heal from the bottom up (secondary intention). Closing it seals the bacteria in.
Dogs & cats
Most bites come from dogs and cats. Cat bites carry a high infection risk. Their needle-like teeth drive bacteria deep, and roughly one in three cat bites gets infected, so get a cat bite seen early even when the wound looks small. Dog bites get infected less often but still need thorough irrigation. For the rabies assessment, find out whether the pet's shots are current.
Wild mammals (bear, mountain lion)
Expect crushing and tearing injuries with severe tissue damage, often with major bleeding and deep wounds. Treat it as major trauma until a hospital says otherwise.
Rodents & rabbits
Small puncture wounds with a low rabies risk. Irrigate them clean. Infection risk is low to moderate. Rabies from rodents and rabbits is close to unheard of, but low risk isn't zero.
Human bites
The human mouth is full of bacteria (oral flora), so these carry a high infection risk. They're dirtier than many animal bites. Irrigate thoroughly, evacuate, and do not close the wound.
Rabies assessment & management
Once symptoms appear, rabies is virtually always fatal. Before that, post-exposure prophylaxis (PEP) works very well.
First step in the field: Wash any bite or scratch from a possibly rabid animal right away with soap and water, hard, for several minutes. Vigorous washing significantly lowers the risk of rabies transmission. Do it before anything else.
| Risk Category | Animal Examples |
|---|---|
| High risk | Bats, raccoons, foxes, skunks, coyotes, unvaccinated dogs and cats |
| Low risk | Rodents (squirrels, rats, mice), rabbits and hares (lagomorphs) |
Post-exposure prophylaxis (PEP)
PEP is a series of rabies vaccines (current versions use 4 doses over 14 days for most people), plus rabies immunoglobulin for anyone who hasn't been vaccinated against rabies before. Start it as soon as possible after exposure, ideally within days. There's no cutoff. Someone who shows up weeks after exposure should still get PEP as long as they haven't developed symptoms. If someone gets bitten in the backcountry, end the trip and get them to care to start PEP. It can't wait for the end of the trip, but it isn't a race either. Don't take risks to get out faster, and don't finish the trip first either. Nothing in the field replaces hospital-based PEP.
Special consideration: bat exposure
Bats have tiny teeth, and people can miss the bite. If a bat turns up in the room with someone who was asleep, and that person can't rule out direct contact, standard public health guidance is to assume a possible exposure and go ahead with a rabies PEP evaluation. Don't write it off.
Reporting requirements
Report every significant animal bite to the local health department, especially bites from wild animals or unvaccinated pets. They'll assess the rabies risk and arrange testing of the animal if they can.
Bear and mountain lion attacks
These are severe trauma. First make sure the animal is no longer a threat, then get the patient out safely. Scene safety includes the bear. Treat it as major trauma, and focus on stopping the bleeding and managing shock. Expect crush injuries, cuts to several parts of the body, and possible damage to major vessels. Emergent evacuation.
Venomous Snakebite Management
North American venomous snakes
| Species | Characteristics | Venom Type & Effects |
|---|---|---|
| Pit vipers: rattlesnakes, copperheads, cottonmouths | Heat-sensing pits between the eyes and nostrils, a triangular head, and rattles (rattlesnakes) | Hemotoxic: local tissue destruction, swelling that keeps spreading, clotting problems (coagulation abnormalities), bleeding |
| Coral snake | Red, yellow, and black bands, a small mouth, no rattles, and a docile temper | Neurotoxic: nerve symptoms that come on late, often with few local signs at first |
Coral snake identification
On a coral snake the red and yellow bands touch. On harmless look-alikes such as the kingsnake, red touches black. The rhyme only holds for US coral snakes, and nobody should get close enough to a snake to read its bands.
Signs of envenomation
Local signs (pit viper)
- Fang marks (there may be 1-4, depending on the strike angle)
- Pain at the bite site, right away
- Swelling that spreads over minutes to hours
- Mark the edge of the swelling with a pen and write the time, every 15 minutes, so you can see how fast it's moving
Systemic signs (pit viper)
- Nausea and vomiting
- Weakness and fatigue
- Numbness and tingling (paresthesias), often around the mouth (perioral)
- Bleeding or bruising away from the bite (coagulopathy)
- Low blood pressure, fast heart rate, shock
Systemic signs (coral snake)
- Delayed onset (it may take hours)
- Drooping eyelids (ptosis)
- Double vision (diplopia)
- Paralysis of the breathing muscles (respiratory paralysis), the most dangerous sign
- All of this can happen with few local symptoms at first
Dry bite
About 20% of pit viper bites inject little or no venom (a "dry bite"). You can't tell which in the field. Every snakebite evacuates now. The 8–12 hours of observation happen at medical care, or on the way there. Nobody calls a bite dry at the trailhead. It's called in hindsight, and your serial swelling marks help make that call, so document them.
Correct field management for pit viper bites
- Calm the patient and keep them at rest. Movement spreads venom faster.
- Take off jewelry and tight clothing. The swelling is coming, so get anything constricting off while you still can.
- Immobilize the limb at heart level. Splint or sling it so it can't move. Keep it at about heart level, not raised and not hanging down.
- Mark the swelling with a pen and the time, every 15 minutes. One line tells you where the swelling is. A series tells you whether it's climbing, and that record guides treatment decisions.
- Evacuate now. Antivenom is the only real treatment, and it has to be given in a hospital. Every snakebite is at least urgent, and it's emergent if symptoms are building (swelling racing up the limb, nausea, vomiting, dizziness, trouble breathing).
- By mouth: No food. Small sips of water are fine if they're alert and the wait is long. Nothing at all if they're vomiting, drowsy, or getting worse.
- Monitor vital signs. Reassess XABCDE every 5 minutes while anything is changing and every 15 once they're stable, and watch for systemic signs.
- Cut an X over the fang marks and suck. It doesn't work, and it adds tissue damage and infection.
- Use commercial suction or venom-extractor devices (e.g., Sawyer Extractor). They don't remove venom, and they can make tissue damage worse.
- Apply a tourniquet. It can cause more tissue damage than the venom itself.
- Apply ice. It causes frostbite and makes tissue damage worse. (Ice is fine on a bee sting. Not on a snakebite.)
- Use electric shock. There's no evidence it helps, and it causes burns.
- Put a constriction band or compression wrap on any snakebite. They can increase local tissue damage and the risk of compartment syndrome.
- Chase, kill, or try to capture the snake. A second bite makes two patients.
Coral snake bites: same field management
At this course's level, treat every suspected snakebite the same way, pit viper or coral snake. Take off jewelry and tight clothing, splint and immobilize the bitten limb at heart level, keep the patient calm and at rest, and evacuate now. Do not apply a constriction band or compression wrap of any kind. A constriction band and pressure immobilization bandaging are two different things.
PIB is a specialized elastic-wrap technique that trained providers use for some elapid snakebites, mainly outside North America. Using it for North American coral snakes is controversial, and the evidence behind it is limited. This course does not teach it, so don't attempt it.
Antivenom
Antivenom is given only in a hospital. Modern pit viper antivenom (CroFab, Anavip) works very well if it goes in early. Coral snake antivenom is used less often, and doctors give it carefully because of possible adverse reactions. Anyone bitten by a possibly venomous snake gets evacuated to a hospital for evaluation and possible antivenom, whatever their early symptoms.
Insect Stings & Spider Bites
Hymenoptera stings: bees, wasps, yellow jackets, hornets, fire ants
Bee stingers
Honeybee stingers are barbed. They stay in the skin and keep injecting venom after the bee has flown off. Get the stinger out fast. Flick it, scrape it, pull it, whatever's quickest. Speed over method. The venom sac keeps pumping the whole time, so don't go looking for a credit card to scrape it with.
Local reaction
Pain, redness, and swelling at the sting. Treat it with ice, NSAIDs, and an antihistamine or corticosteroid cream.
Large local reaction
Swelling that spreads far past the sting, sometimes reaching the joints, like a hand sting that swells the whole arm. It's a localized hypersensitivity reaction, not anaphylaxis. Treat it with an oral antihistamine, and get a medical evaluation if the swelling is severe or still spreading. Watch for anaphylaxis (see Lesson 10).
Fire ants
Fire ant stings leave sterile pustules. Don't pop them, because that lets infection in. Left alone, they usually clear up on their own.
Black widow spider envenomation
Identification
A shiny black spider with a red hourglass on the abdomen. The body's about the size of a pea.
Venom & effects
Black widow venom is neurotoxic (alpha-latrotoxin). It forces nerve endings to dump acetylcholine uncontrollably, and that causes the classic symptoms.
Signs & symptoms
- Pain at the bite, often minimal at first
- Severe, painful muscle cramps spreading from the bite, within 30 minutes to hours
- The classic sign is a rigid, board-hard belly as the abdominal muscles cramp, but cramping can hit any muscle group
- Sweating (diaphoresis), high blood pressure, fast heart rate
- Nausea and vomiting
- Pain in the thighs and chest
- Possible breathing trouble if the respiratory muscles are involved
Field management
Manage the pain with NSAIDs and ice, and watch for respiratory distress. Evacuate (urgent). Hospitals carry black widow antivenom, and it works very well.
Brown recluse spider envenomation
Identification
A brown spider with a violin-shaped marking on the front body section (cephalothorax). It has 6 eyes arranged in pairs. Most spiders have 8.
Check where you are. Brown recluses live only in the south-central and midwestern United States. A spider that doesn't live in your state is a poor suspect. Outside that range, most suspected "recluse bites" turn out to be something else, often a skin infection such as MRSA. Even inside recluse territory, confirmed severe necrosis is uncommon.
Venom & effects
Brown recluse venom is cytotoxic. It kills tissue (necrosis), and the dying tissue leaves the classic "sinking" or "volcano" lesion.
Signs & symptoms
- A painless bite at first (it may go unnoticed)
- 2-8 hours: pain starts, redness develops, a blister forms
- 24-72 hours: a blue-black dead (necrotic) center forms, and the lesion "sinks" as the tissue dies
- Systemic symptoms are rare but possible: fever, and hemolysis (extremely rare)
- The lesion can be disfiguring
Field management
Clean the wound, apply ice, and mark the edge of the lesion with a pen so you can see whether it's growing. Evacuate for medical evaluation. There's no brown recluse antivenom in the United States, so the hospital treats the wound and works to prevent infection.
Black widow vs. brown recluse
| Feature | Black Widow | Brown Recluse |
|---|---|---|
| Venom type | Neurotoxic | Cytotoxic |
| Bite pain | Often minimal | Painless at first |
| Primary effect | Muscle cramps, systemic symptoms | Tissue necrosis at the bite site |
| Onset | Minutes to hours | Hours to days |
| Antivenom | Available | Not available in the US |
Tick Removal & Tick-Borne Illness
Removing a tick
Grab the tick with fine-tipped tweezers as close to the skin as you can, and pull steadily upward. Don't twist it, crush it, or use petroleum jelly, alcohol, or heat. Those methods stress the tick and may make it inject more pathogen.
After removal
- Clean the bite with soap and water
- Wash your hands
- Seal the tick in a plastic bag if you can, in case it needs testing later
- Don't crush the tick with bare hands
- Watch for a rash or fever over the next few weeks. If either shows up, see a doctor and tell them about the tick.
Disease transmission timeline
Lyme disease usually needs the tick attached for 36 hours or more to transmit, and the risk climbs steeply after 48 hours. Some other tick-borne diseases transmit faster. Either way, prompt removal significantly lowers the risk of transmission, and sooner is better.
Tick-borne diseases
| Disease | Tick Vector | Key Clinical Features |
|---|---|---|
| Lyme Disease | Deer tick (Ixodes) | Bull's-eye rash (erythema migrans), flu-like symptoms, arthritis; can involve the central nervous system (CNS) |
| Rocky Mountain Spotted Fever | Dog tick, wood tick | Rash that starts at the wrists and ankles and spreads toward the trunk, fever, headache; can be fatal if untreated |
| Ehrlichiosis | Lone Star tick | Fever, headache, muscle aches (myalgia), sometimes a rash, low platelets (thrombocytopenia) |
| Anaplasmosis | Black-legged (deer) tick | Similar to ehrlichiosis: fever, headache, muscle aches, abnormal lab results |
Marine Envenomation
Jellyfish stings
Jellyfish tentacles carry stinging cells (nematocysts) that fire venom into the skin when something sets them off. Treat a sting this way.
- Rinse with salt water, not fresh water. Fresh water can make the nematocysts fire.
- Don't use urine. It doesn't help, and it can make more nematocysts fire.
- Pull off visible tentacles with tweezers, not bare hands.
- Vinegar helps deactivate box jellyfish stings, but it can make some other species' stings worse. Use it only when you know a box jellyfish did it.
- If you don't know the species, rinse with seawater, remove the tentacles with tweezers, then soak it in hot water (45°C / 113°F) for 20-45 minutes for the pain.
Stingray injury
A stingray spine makes a puncture wound and injects venom, usually into the foot or ankle. The pain is severe.
- Soak the limb in hot water (45°C / 113°F) for 30-90 minutes. Test it on your own skin first so you don't scald them. Do this before you worry about getting the spine out.
- Irrigate the wound.
- Remove the barb if you can reach it without causing more injury.
- Evacuate for wound care and a check for deeper injury.
Sea urchin spines
Sea urchin spines lodge in the skin and can break off. They can be toxic and irritating.
- Pull out the spines you can reach with tweezers.
- Soak it in hot water (45°C / 113°F).
- Evacuate if several spines are embedded or there's a risk of infection.
Scenario-Based Learning
Setting: A hiker 5 miles from the trailhead says a snake bit them on the ankle. They think it was a rattlesnake. You get there 10 minutes after the bite. The ankle is swollen and bruised, with two fang marks, and the patient is anxious and nauseated.
Think it through:
- What are your first assessment priorities?
- What will you do for them in the field?
- What are you not going to do?
- What's your evacuation plan?
- Primary assessment: Make sure the snake isn't still around (scene safety). Run XABCDE. Is their circulation unstable? Are they in respiratory distress? Any signs of systemic envenomation, such as nausea, vomiting, or low blood pressure?
- Secondary assessment: Note the time of the bite. Look at the site. Two fang marks suggest a pit viper. It could be a dry bite, but assume it isn't. Mark the starting edge of the swelling with a pen and write down the time.
- Field care: Get the boot and sock off carefully before the ankle swells into them. Take off any jewelry, rings included. Immobilize the limb with the ankle at about heart level, not elevated. No food. Small sips of water are fine while they're alert, since the wait could be hours.
- What not to do: No cutting and sucking. No tourniquet or constriction band. No ice. Don't try to kill or capture the snake.
- Evacuation: 5 miles from the trailhead at 30 minutes a mile is about 2.5 hours, and every step the patient walks is exertion you're trying to avoid. Carry them if you have the people. A slow walk-out is the last resort. Evacuate now. It's urgent at minimum, and emergent the moment systemic signs show up. If you have a satellite communicator, use it now to call for rescue, and ask for a helicopter if one's available and the weather allows.
- Monitoring: Check vitals every 5 minutes while symptoms are changing, every 15 if they're stable. Re-mark the swelling every 15 minutes. Watch for signs of systemic envenomation. Keep the patient at rest and keep reassuring them. Anxiety revs up the body's stress response, and that can make symptoms worse.
- At the hospital: Every pit viper bite needs a hospital evaluation for possible antivenom, whatever the symptoms. Even a dry bite needs a period of observation.
Setting: You're on camp staff. In the morning, a cabin of 8 campers (ages 12-15) tells you a bat was in the cabin with them overnight. Nobody reports a bite, but several of them slept soundly through the night. The bat has flown off.
Think it through:
- Is this a rabies exposure?
- What do you need to do?
- Yes, this is a rabies exposure. Bats have tiny teeth and can bite a sleeping person without anyone noticing. Standard public health guidance says that if a bat is found in a room with a sleeping person and direct contact can't be ruled out, you assume a possible exposure.
- Don't dismiss it. No visible bite does not mean no exposure.
- Right now: Call the local health department and the camp's medical director. All 8 campers need evaluation for post-exposure prophylaxis (PEP).
- Families: Call every camper's parents or guardians right away. Write down when the bat was found, which campers were in the cabin, and any symptoms.
- The bat: Don't try to catch or kill it. That's one more chance for someone to get bitten. If it's already contained, call public health for safe handling and possible testing.
- Next steps: End the trip and get every camper to medical care. PEP has to start as soon as possible after exposure. Today's vaccines are much safer than the old ones.
Knowledge Check
10 questions. Pick an answer to get immediate feedback. Answer order is shuffled each attempt, and your best score is saved on this device.
Lesson Summary
Key takeaways
- Irrigate every animal bite aggressively and leave it open to drain. Don't close it in the wilderness.
- A bat in the room with a sleeping person means you assume exposure, and that needs a PEP evaluation even with no visible bite.
- For a pit viper bite, get jewelry off, immobilize, mark the swelling edge with the time, and evacuate now for antivenom. No cutting, sucking, tourniquet, ice, or constriction, and don't chase the snake.
- Coral snake bites are neurotoxic. They may show few local signs and still cause respiratory failure. Manage them like any snakebite: immobilize at heart level, no bands or wraps, evacuate now.
- Get bee stingers out fast. Speed matters more than method.
- Black widow venom causes muscle cramps and systemic symptoms. Brown recluse venom causes local tissue necrosis.
- Pull ticks out promptly with fine tweezers and a steady upward pull. Lyme usually needs 36+ hours of attachment, but some diseases transmit faster. The sooner it's out, the lower the risk.
- At the coast, rinse jellyfish stings with salt water and soak stingray and sea urchin wounds in hot water.
Glossary of terms
- Envenomation
- An animal (snake, spider, insect) injecting venom into tissue.
- Hemotoxin
- Venom that acts on the blood and circulatory system. It destroys tissue around the bite and disrupts clotting. Typical of pit vipers.
- Neurotoxin
- Venom that acts on the nervous system and can cause paralysis. Typical of coral snakes and some spiders.
- Antivenom
- Antibodies against a specific venom, given by IV in a hospital to counteract envenomation. Used for pit vipers, black widows, and other serious bites.
- Rabies
- A viral infection spread through saliva. Nearly always fatal once symptoms appear, and preventable with post-exposure prophylaxis.
- Post-Exposure Prophylaxis (PEP)
- A series of vaccines, plus immunoglobulin for people never vaccinated against rabies, given after a possible exposure to prevent infection.
- Dry Bite
- A venomous snakebite that injects little or no venom. It happens in about 20% of pit viper bites and is diagnosed in hindsight, after 8–12 hours of observation at medical care.
- Black Widow Spider
- A venomous spider with a distinctive red hourglass marking. Its venom is neurotoxic and causes muscle cramps and systemic symptoms.
- Brown Recluse Spider
- A venomous spider with a violin-shaped marking. Its venom is cytotoxic and causes local tissue necrosis in a "sinking lesion" pattern.
- Tick-Borne Illness
- Infections that ticks pass on when they bite, including Lyme disease, Rocky Mountain spotted fever, ehrlichiosis, and anaplasmosis.
- Necrotizing
- Causing tissue death. Characteristic of brown recluse venom.
- Pressure Immobilization
- A specialized elastic-bandage technique that trained providers use for some elapid snakebites to slow the spread of venom through the lymphatics. It's controversial, with limited evidence for North American coral snakes. It's listed here so you recognize the term. This course doesn't teach it.
Wilderness Medicine: Beyond First Aid (7th ed.) - William Forgey
CDC Rabies Information: cdc.gov/rabies
UpToDate: Snakebite, Tick Removal, Marine Envenomation