Dangerous Insects for Pets in the UK
The UK is home to a range of insects and invertebrates that can injure, irritate, or poison pets. While serious envenomation is less common in Britain than in some other countries, several insects cause injuries that require veterinary attention — and some can trigger life-threatening anaphylactic reactions in sensitive animals. Climate change has also introduced new invasive species to parts of the UK and Europe that pose additional risks.
Wasp and Bee Stings
Dogs and cats — especially curious, playful animals — frequently get stung by wasps and bees when investigating flowers, overripe fruit on the ground, or outdoor feeding areas. A single sting typically causes localised swelling, pain, and redness. Dogs most commonly get stung on the face, mouth, or paws.
Multiple stings or a sting inside the mouth or throat are more serious. Airway swelling can cause breathing difficulties and is a veterinary emergency. Some animals are allergic to insect stings and can develop anaphylaxis — a rapid, severe whole-body allergic reaction that causes collapse, pale gums, vomiting, and difficulty breathing. This can be fatal within minutes without treatment.
If you notice facial swelling, hives, difficulty breathing, or collapse after a suspected sting, go to an emergency vet immediately. A single sting on the paw or body with mild swelling can usually be managed at home by removing the stinger (if visible), applying a cold compress, and monitoring.
Ticks
Ticks are small arachnids (closely related to spiders) that attach to the skin to feed on blood. They are common in long grass, woodland edges, moorland, and deer habitats across the UK, and are most active between spring and autumn. Dogs are most commonly affected, but cats that roam outdoors are also at risk.
The primary concern with ticks is not the bite itself but the diseases they can transmit. Lyme disease (caused by Borrelia burgdorferi bacteria) is the most significant tick-transmitted disease in UK pets and humans. Symptoms in dogs include lameness, joint swelling, fever, and lethargy appearing weeks after the bite.
Always check your pet thoroughly after walks in tick habitats. Remove attached ticks promptly using a tick removal hook (never with tweezers or by burning) by rotating the hook anticlockwise without squeezing the body. Consult your vet about appropriate tick prevention products.
Horse Flies
Horse flies (Tabanus species) are large, powerful biting flies that cut through skin rather than piercing it, making their bites extremely painful. Unlike mosquitoes or midges, horse flies can bite through thin fur. Bites cause immediate sharp pain, followed by swelling, localised heat, and irritation. Horses and dogs are most frequently affected.
Serious complications are uncommon but include severe local reactions, secondary infection from excessive scratching or licking, and in very rare cases, an allergic response. Topical wound care is usually sufficient for uncomplicated bites. If swelling is significant or the bite becomes infected (increasing redness, discharge, warmth), contact your vet.
Oak Processionary Moth Caterpillars
Oak processionary moth (Thaumetopoea processionea) caterpillars carry fine, barbed hairs containing a protein called thaumetopoein that causes significant irritation on contact with skin, eyes, and mucous membranes. They are most active from April to July and are found primarily in oak trees across London and the South East of England, though their range is expanding.
Contact causes intense itching and rash on the skin, redness and discharge from the eyes, and — if the hairs are inhaled or ingested — severe inflammation of the throat and airways. Dogs that sniff or lick caterpillar nests on the ground or on trees can be badly affected. If your dog shows signs of drooling, swollen tongue, difficulty breathing, or severe itching after contact with caterpillars, seek urgent veterinary care.
False Widow Spiders
False widow spiders (Steatoda species), particularly Steatoda nobilis, have become increasingly common in the UK, especially in the south. They can bite if handled or disturbed. While their venom is less potent than that of true black widow spiders, a bite can cause localised pain, swelling, redness, and in some cases systemic symptoms including nausea and muscle cramps.
If your pet is bitten by a spider and shows significant swelling, appears unwell, or is in pain, contact your vet. Take a photograph of the spider if possible to aid identification.