First aid for all spider envenomation (other than funnelweb or mouse spider) is washing the site and analgesia.

Necrotising arachnidism is a condition of persistent and refractory ulceration subsequent to a spider bite, although aetiology is often unclear. The species responsible is also often subject to some doubt. Species which more commonly bite humans are the white-tailed spider, the black house spider, huntsmen, wolf spiders and orb-weaving spiders.

Signs and Symptoms Blistering around the bite site Ulceration Necrosis Treatment There remains no definitive treatment for necrotising arachnidism. It is best to view the treatment of such lesions as one would for any ulcer requiring local wound care.

Specific treatment should be inaccordance with the pathology of the ulcer. Photographs may be helpful in tracking its progress. Ulcer pathogenesis may take time to identify and it is best not to diagnose necrotising arachnidism without thoroughly considering differential diagnosis.

Differential Diagnoses

• Vascular ulcers: arterial or venous insufficiency
• Diabetic ulcer
• Neuropathic ulcer
• Microbial infection
• Foreign body
• Focal and general vasculitis
• Injection of toxin (accidental or deliberate)
• Drug reaction
• Physical/mechanical trauma (may be deliberate)
• Bed sores
• Burns (especially chemical burns)
• Contact dermatitis
• Pyoderma gangrenosum
• Neoplasm
• Connective tissue diseases
• q₁-antitrypsin deficiency
• Other arthropod bites or stings