• Venomous spiders are found in many countries including the USA and Australia.
• Spider bites are considered rare but may be fatal, especially if multiple.

Presenting signs

• Envenomation by spiders of the genusLatrodectus, including the Black Widow in North America, the Red Back in Australia and the Katipo in New Zealand, is associated with excitability, spasms and rigidity of muscles, ascending motor paralysis, and hypersalivation.

• Envenomation by Brown Recluse spiders (Loxosceles reclusa) in North America causes a necrotic arachnidism. The site of the bite is likely to ulcerate and take a long time to heal.
• Necrotic arachnidism has been suspected in Australia and attributed to bites by the Fiddleback spider (Loxosceles rufescens) or the White Tailed spider.

• Rarely, Loxosceles envenomation may result in fever, nausea, seizures Seizures , or hemolysis with hemoglobinuria Hemoglobinuria.

Acute presentation

• Latrodectism: excitability, hyperesthesia, muscle rigidity, may be convulsions or paralysis.
• Necrotic arachnidism: ulcerated wound, refractory to healing.

Geographic incidence

• North America:Latrodectus mactans(Black Widow),Latrodectus hesperus,Loxosceles reclusa(Brown recluse), otherLoxoscelesspecies.Latrodectusspecies are most common in the Southwest and are most prolific in warm climates with mild winters.Loxoscelesspecies are found throughout the United States.

• Australia:Latrodectus mactans hasselti(Red Back) are found in all states of Australia. White Tailed spiders(Lamplonaspecies) are common in houses throughout Australia.
• Other spiders in Australia known to inflict painful, but not otherwise hazardous bites are the Black House Spider (Badumna insignis), Huntsman spiders (various species), Wolf spiders (various species) Orb Weaving spiders (various species) and Trapdoor spiders (various species).
• The Funnel Web Spider found in the area of Sydney, Australia, is highly dangerous to humans and other primates, but there have been no reports of fatal Funnel Web spider bites in domestic animals. Experimentally, dogs have tolerated very large doses of Funnel Web venom with no clinical signs, or with transient tachycardia and hypertension.

• New Zealand:Latrodectus mactans hasselti(Katipo) is generally associated with coastal areas. White Tailed spiders have been accidentally introduced from Australia in the last decade with a corresponding rise in cases of suspected necrotic arachnidism in people. Black House spiders have also been accidentally introduced from Australia.

• Latrodectusspecies are also found in the Mediterranean area and in Africa, Asia, India and South America. The karakurt isLatrodectus tredecimguttatus.

Age predisposition

• No age, gender or breed predisposition reported.
• Loxoscelesspiders tend to roam at night and would be most likely to bite dogs sleeping on the floor of a house.

Public health considerations

• LatrodectusandLoxoscelesspiders are also a risk to human beings.Latrodectusbites cause significant morbidity in human beings.
• MultipleLoxoscelesbites can be fatal particularly to children.

Cost considerations

• Treatment costs are moderate to expensive.
• Loxoscelesbites may require prolonged treatment.