Brown recluse spider bites in Pets

Brown recluse bites can cause slow-healing skin wounds and, rarely, blood and organ problems. Learn how the lesion develops over days, simple wound care and when to see a vet.

What It Is

Recluse spiders (Loxosceles) are brown, long-legged spiders, often with a violin-shaped mark on the back and six eyes arranged in pairs. Their venom contains sphingomyelinase D and other enzymes that destroy tissue around the bite and can, less often, damage red blood cells, clotting and organs.

Where Pets Come Across It

The brown recluse lives in the south-central and midwestern US, hiding in closets, attics, boxes, bedding and woodpiles. Related species occur in South America, the Mediterranean and Africa. Bites often happen when a pet lies on a spider.

Which Animals Are Affected

Dogs and cats. Pet Poison Helpline describes the spider as 8–13 mm long with legs of 20–30 mm.

Published Toxic Dose

No owner-usable dose exists; the venom injected is unknown and many suspected bites turn out to be other skin conditions. The Merck Veterinary Manual notes that diagnosis relies on geography, signs and ideally identification of the spider. So the calculator does not grade it.

Signs and How Soon They Appear

The bite may not hurt at first. Over hours to days, the area becomes red, itchy and painful, often forming a 'bull's-eye' with a pale or dark centre that can ulcerate and heal slowly. Less commonly there is fever, lethargy, vomiting, bruising, dark urine or organ damage.

What to Do Right Now

Clean the area gently with soap and water, prevent licking, and call your vet. Go sooner if the wound spreads quickly or your pet becomes lethargic, feverish or passes dark urine. Collect the spider in a jar if it is safe to do so.

Where recluse spiders live, and what else causes similar wounds

In the US the brown recluse is mainly found in a band of south-central and midwestern states, from Texas and Oklahoma to Missouri, Kentucky and Tennessee. Outside that range, confirmed bites are rare, and many 'spider bites' turn out to be bacterial skin infections, including MRSA in people, or other causes such as burns or insect stings. In homes where recluses live, they hide in cardboard boxes, wardrobes, behind furniture and in bedding, which is why pets lying in quiet corners can be bitten. Shake out pet bedding and blankets stored in garages, use sticky traps to monitor numbers, and reduce clutter. Whatever the cause, a skin wound that spreads, darkens or does not heal needs a vet's examination.

Frequently Asked Questions

Sources and References

• Merck Veterinary Manual: Spider and Scorpion Bites and Stings
• Pet Poison Helpline: Brown Recluse Spider

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