CONDITION
Adder Bites
An adder bite occurs when a dog or cat is bitten by Britain's only venomous snake, the European adder (*Vipera berus*). The venom can cause local tissue damage and, in some cases, effects throughout the body. Adders are generally shy and bites tend to happen during warmer months when both snakes and pets are active outdoors, often in heathland, moorland, or woodland. Owners may notice sudden pain or distress, swelling that develops around the bite site—most commonly on the face, neck, or limbs—and sometimes puncture marks. Signs can range from mild local swelling to more widespread effects such as vomiting, lethargy, or pale gums, depending on factors like the amount of venom injected and the size of the animal. Cats are bitten less frequently than dogs, but may show similar patterns. This page explores what an adder bite may look like when it occurs, what happens in the body after envenomation, how the condition is investigated, and the approaches used to support affected animals during recovery.
Why this matters now
Adder bites typically occur during the warmer months, from late February through October, when adders have emerged from hibernation and both snakes and pets are active outdoors. The peak period often coincides with spring and summer walks in habitats where adders bask and hunt—heathland, moorland, woodland edges, rough grassland, and coastal dunes. Dogs of any age or breed can be bitten, though curious or energetic individuals may encounter adders more frequently. Cats are bitten less often, likely because they tend to avoid open basking areas and may be more cautious around unfamiliar movement.
Signs usually begin within two hours of the bite, though in some cases swelling may start within minutes. The initial local reaction—pain, distress, and swelling at the bite site—can progress over the following hours, and in some animals systemic effects such as lethargy, vomiting, or changes in heart rhythm may develop within the first twelve hours. The course varies considerably between individuals, influenced by factors such as the amount of venom injected, the location of the bite, and the size of the animal. Many animals show gradual improvement over several days, though swelling and discomfort may persist for longer.
Signals & patterns
Early signals
Sudden distress or yelping
An owner may notice their dog or cat react sharply to something underfoot or in the grass, often with a sudden cry or jump. This immediate pain response can occur even before any visible swelling appears, and the animal may lick, paw at, or favour the affected area.
Localised swelling
Swelling tends to develop around the bite site, most commonly on the face, muzzle, neck, or limbs. The area may feel warm and firm to the touch, and in some cases two small puncture marks can be seen at the centre, though these are not always visible.
Increased drooling or licking
Animals bitten on the face or mouth may drool more than usual, and those bitten elsewhere may repeatedly lick the affected area. This behaviour often reflects discomfort or the sensation of swelling and heat in the tissues.
Restlessness or altered behaviour
Some animals become restless, pacing or unable to settle, while others may seem quieter than usual or reluctant to move. These changes in demeanour can reflect pain, nausea, or the early effects of venom on the body.
Later signals
Lethargy and weakness
As hours pass, many animals become noticeably more tired or unsteady, sometimes struggling to stand or walk normally. This can reflect the systemic effects of venom on circulation and the body's effort to respond to inflammation and fluid shifts.
Vomiting or pale gums
Some animals develop vomiting, and the gums may appear paler than usual or take longer to return to their normal colour after gentle pressure. These signs can indicate that the venom is affecting blood vessels and circulation more widely.
Increased heart or breathing rate
An owner may notice faster breathing or a more rapid heartbeat, and in some cases irregular heart rhythms or heart murmurs can develop. These changes reflect the body's response to pain, inflammation, and shifts in fluid balance.
Click to read about the biological mechanisms
How this is usually investigated
The diagnosis of an adder bite typically begins with the history—the timing, location, and any witnessed interaction with a snake—and observation of the developing signs. Physical examination focuses on identifying puncture wounds, documenting the extent and progression of swelling, and assessing the animal's overall cardiovascular and neurological state. Laboratory tests may be used to evaluate the severity of systemic effects and to guide supportive care, though there is no specific test that confirms envenomation.
Physical examination
Complete blood count
Chemistry panel
Blood pressure measurement
Electrocardiography
Options & trade-offs
Management of adder bites is largely supportive, aiming to maintain cardiovascular stability, control pain and inflammation, and allow the body to clear venom and repair tissue. The combination of approaches used depends on the severity of signs, the rate of progression, and the individual animal's response. Some animals recover with minimal intervention, while others require more intensive monitoring and support over several days.
Intravenous fluid therapy
Fluids are given through a vein to support blood pressure, maintain kidney perfusion, and replace volume lost into swollen tissues. The rate and duration are adjusted according to the animal's cardiovascular status and laboratory findings. Fluid therapy is often continued until swelling begins to resolve and the animal is drinking and eating reliably.
Trade-offs: Intravenous access requires placement of a catheter and monitoring to avoid over- or under-hydration, which can complicate recovery in animals with significant fluid shifts. Prolonged fluid therapy may require hospital admission, and some animals develop phlebitis or catheter-site complications.
Analgesia and anti-inflammatory medication
Pain relief is provided using opioid analgesics, sometimes in combination with non-steroidal anti-inflammatory drugs once the animal is stable and well-hydrated. These medications reduce discomfort and may help limit the inflammatory response to venom. The choice and dose are tailored to the individual, and adjustments are made as signs evolve.
Trade-offs: Non-steroidal anti-inflammatory drugs carry a risk of kidney or gastrointestinal side effects, particularly in animals with borderline renal function or dehydration, so their use may be delayed or avoided in more severe cases. Opioids can cause sedation or nausea in some individuals.
Antivenom (European viper antivenom)
Antivenom is a preparation of antibodies that bind and neutralise adder venom components. It is given intravenously, typically within the first hours after the bite, and may reduce the severity and duration of systemic signs in moderately to severely affected animals. Use has declined in recent years due to limited availability and questions about cost-effectiveness in all cases.
Trade-offs: Antivenom can cause allergic or anaphylactic reactions, and animals receiving it require close monitoring during and after administration. Its benefit appears greatest when given early and in animals with more severe signs, but many animals recover fully without it, and access can be limited.
Wound care and monitoring
The bite site is kept clean and assessed regularly for signs of infection or tissue necrosis. In most cases, swelling resolves gradually without the need for surgical intervention. Cold compresses are sometimes used in the first hours to provide comfort, though their effect on venom spread is uncertain.
Trade-offs: Extensive swelling can make wound assessment difficult, and in rare cases severe tissue damage may lead to skin sloughing or abscess formation that requires debridement. Overly aggressive local treatment, such as incision or suction, is not helpful and may worsen tissue injury.
Hospitalisation and supportive care
Animals with moderate to severe signs are often admitted for observation, allowing serial assessments of cardiovascular and neurological status, adjustment of fluid rates, and early detection of complications such as arrhythmias or worsening kidney function. The duration of admission varies from one to several days, depending on the trajectory of recovery.
Trade-offs: Hospital care provides close monitoring and rapid access to interventions, but it involves separation from the home environment and can be stressful for some animals. Costs accumulate with longer stays, and not all animals require intensive monitoring to recover.
Common misconceptions
"All adder bites are life-threatening and require antivenom to survive."
The severity of adder bites varies widely, and many animals develop only local swelling and discomfort that resolves with supportive care alone. Antivenom is considered in more severe cases, but it is not universally required and many dogs and cats recover fully without it. The decision to use antivenom depends on the individual animal's signs and the progression of effects.
"Applying a tourniquet or cutting the wound will stop the venom from spreading."
Tourniquets can restrict blood flow and worsen tissue damage, and cutting or suctioning the bite site does not remove venom and may introduce infection or cause further injury. Adder venom spreads through the tissues and lymphatics within minutes, and the priority is to keep the animal calm and seek veterinary assessment rather than attempt local intervention.
"Cats are immune to adder venom or do not get bitten."
Cats can be bitten by adders and can develop similar local and systemic signs to dogs, though bites in cats appear to be less common, possibly due to behavioural differences. There is no evidence that cats are immune to the venom, and affected cats may require the same supportive care as dogs.
Related conditions
Anticoagulant Rodenticide Toxicity
Anticoagulant rodenticide toxicity can produce bleeding and clotting problems that may resemble some of the systemic effects seen after significant adder envenomation, though the underlying mechanisms differ—one involves blocked vitamin K recycling, the other direct venom effects on blood vessels and cells.
Acute Kidney Injury
Acute kidney injury can develop in some cases following adder envenomation, particularly when venom causes widespread breakdown of red blood cells or low blood pressure affects kidney perfusion. Monitoring kidney function is part of assessing the extent of systemic involvement after a bite.
Acute Moist Dermatitis (Hot Spots)
Acute moist dermatitis may occasionally be confused with the localised swelling and skin damage at an adder bite site, particularly if the puncture marks are not visible and the tissue becomes moist or inflamed quickly. The distribution, history, and progression tend to distinguish the two.
Babesiosis
Babesiosis can cause breakdown of red blood cells and systemic signs such as lethargy, pale gums, and sometimes collapse, a pattern that overlaps with some presentations of adder bite. Both conditions may warrant blood work to assess red cell counts and evidence of haemolysis.
Once the acute phase has passed, attention often shifts to the resolution of swelling, return to normal activity, and any lingering effects such as skin sloughing or secondary infection at the bite site. Some animals take several weeks to recover fully, and the experience may inform decisions about walking routes or supervision during peak adder season. Understanding the range of outcomes and the factors that influence recovery can be a useful part of the conversation during follow-up.
Last reviewed: 12 September 2026 · Dr Alastair Greenway MRCVS