Spider Bites

Updated (2026-07-23) against the current NSW Health Snake and Spider Bites Clinical Management guideline (GL2024_007, June 2024).

Spider bites fall into 3 groups:

• Big black spiders (including funnel-web) — manage as a potential medical emergency
• Redback spider — painful but not life-threatening
• All other Australian spiders — minor effects only, no specific treatment

Australian spider bites are very unlikely to cause necrotic skin lesions — a necrotic lesion should be actively investigated for another cause (e.g. infection), not attributed to a spider bite by default.

Big black spider bites (including funnel-web)

All bites by big black spiders (funnel-web, trapdoor, mouse spiders, and other large primitive mygalomorphs) in eastern Australia should be managed as suspected funnel-web spider bites for the first four hours. Funnel-web envenomation is rare (fewer than 15% of bites cause significant envenomation) but potentially rapidly lethal — treat as an acute medical emergency. Reported mainly in the Sydney/Central Coast/Newcastle region, but cases as far as Wauchope in northern NSW.

Clinical features of severe envenomation

• Autonomic excitation — diaphoresis, piloerection, hypersalivation, lacrimation, hypertension/bradycardia or tachycardia, miosis or mydriasis
• Neuromuscular/sensory excitation — fasciculations (classically tongue fasciculation), paraesthesia, muscle spasms
• Other severe effects — decreased GCS, pulmonary oedema, multiorgan failure, hypotension (a later sign)
• Non-specific — agitation, abdominal pain, nausea/vomiting, headache

Management

First aid — same as snake bite: pressure bandage with immobilisation (PBI), limb splinting, complete patient immobilisation. Apply a new PBI over an inadequate one already in place rather than removing it.

In hospital — observe for at least 4 hours after the bite and 2 hours after PBI removal. Keep the bandage in place until the patient is assessed in hospital; only remove it in a critical care area (medical officer/nurse practitioner) once antivenom is available and there’s no clinical evidence of envenomation, or after antivenom has been given.

Investigations — none are routinely needed to diagnose envenomation. If catecholamine-induced cardiomyopathy is suspected (extreme hypertension progressing to hypotension/tachycardia), get troponin, ECG, and echo if hypotensive.

Antivenom — the priority treatment, indicated only for signs of severe envenomation (unlikely beyond 2 hours post-bite). Adverse reactions are rare. Dose: 2 vials, the same for adults and children — reconstitute, dilute, and infuse slowly, watching for erythema/urticaria/hypotension/bronchospasm; if none, increase to a 20-minute infusion. Further doses aren’t usually needed — if there’s no response, seek toxicologist advice. Contact a clinical toxicologist or the Poisons Information Centre (13 11 26) early whenever funnel-web envenomation is possible.

Supportive care — respiratory failure (usually pulmonary-oedema-driven) may need ventilatory support; atropine can help marked cholinergic features if antivenom isn’t immediately available; sedation is first-line for severe hypertension (won’t worsen other poisoning features); atropine/benzodiazepines can manage persistent cholinergic/catecholaminergic symptoms after antivenom.

Disposition — patients given antivenom are admitted and monitored 12–24 hours until envenomation symptoms resolve. Patients without severe signs/symptoms can be discharged once 4 hours have passed since the bite and at least 2 hours since PBI removal.

Redback spider bite

Found in temperate regions across Australia (rare in the far north and Tasmania); prefers dark, dry spots like shoes, helmets and outdoor equipment. The most common significant envenomation in Australia — and not fatal (no deaths reported since the mid-1950s).

Clinical features

• Bite often not felt initially; local pain increases over 1–2 hours, lasting up to 5 days; may radiate via draining lymph nodes to abdomen, chest, back
• Localised diaphoresis is the pathognomonic finding (may also be regional — e.g. bilateral below the knee)
• Nausea, vomiting, headache, malaise, lethargy
• Less common: piloerection, local erythema, fang marks (~5%), hypertension, irritability/agitation, fever, paraesthesia, patchy paralysis, muscle spasms, priapism

Management

First aid — clean the bite site with antiseptic, cover with a light dressing; ice or heat pack for symptom relief (either is reasonable — use whichever is available/preferred). Do not apply a pressure bandage — it worsens the pain.

Analgesia is the mainstay of treatment. Multimodal analgesia may be needed: paracetamol, ibuprofen, opioids, clonidine, patient-controlled analgesia. Topical local anaesthetic can be trialled (minimal evidence, low risk). For troublesome diaphoresis, changing clothing/bedding for comfort.

Antivenom is no longer recommended as initial treatment (RAVE-II RCT found no clinically meaningful benefit over placebo) and is not on the NSW Medicines Formulary — it may only be considered at a senior clinician’s discretion (ideally with toxicologist input) if analgesia fails after 1–2 hours.

Disposition — discharge once pain is adequately managed and the patient is asymptomatic; provide analgesia to take home for up to 5 days.