Necrotic arachnidism?

aka Toxicology Conundrum 018

A 40 year-old man presents to the ‘fast-track’ area of your emergency department. He has a ulcerating sore on his right arm. He says its been getting worse over the past 2 weeks. He mentions there are quite few white-tailed spiders on his property and that he’s pretty sure he got bitten by one while he was gardening. He is otherwise well.


Q1. What are white-tailed spiders and where are they found?

Answer and interpretation

The name white-tailed spider refers to either of the Lampona species, L. cylindrata or L. murina.

Both are dark grey spiders that have a cylindrical body with fairly obscure lateral white patches on the abdomen, but with a definite white spot at its tip.

These species are found throughout Australia and New Zealand. Bites tend to occur in the warmer months, they nearly always occur indoors and usually occur in the evening or at night. The spider is usually encountered between layers of fabric (e.g. in bedclothes, between sheets, or in clothing).

Q2. How do white-tailed spider bites present?

Answer and interpretation

Not with ulcerating or necrotic skin lesions! This is a persistent and misleading myth.

Studies of the venom of Lampona species have failed to find any cytotoxic effects. In Isbister and Gray’s meticulous prospective study of 130 white-tailed spider bites (in each case the spider was caught and identified by an expert arachnologist) there were no ulcers, necrotic lesions or infections found.

The clinical manifestations of white-tailed spider bites include the following:

  • painful bite (all cases in the Isbister and Gray study), sometimes with a small puncture mark.
  • one of the following three types of local reactions may occur:
    • severe local pain lasting 2 hours or less (about 1 in 5 bites)
    • local pain and a red mark lasting less than 24 hours (about 1 in 3 bites)
    • a persistent and painful red lesion, which does not break down or ulcerate, and may last 5-12 days (about 2 out of 5 bites).
  • mild non-specific systemic features of envenoming:
    • nausea, vomiting, headache, malaise.
  • pruritis (itch) occurs in nearly half of cases.

Isbister GK, Gray MR. White-tail spider bite: a prospective study of 130 definite bites by Lampona species. Med J Aust. 2003 Aug 18;179(4):199-202. [PMID 12914510]

Q3. How is a white-tailed spider bite managed?

Answer and interpretation

A ‘true’ white-tailed spider bite can be managed by applying an ice pack and taking oral analgesia (e.g. paracetamol).

Assessment by a doctor is not necessary.

Q4. What is the differential diagnosis in this case?

Answer and interpretation

It is difficult to suggest an appropriate differential diagnosis without taking a complete history or examining the lesion (a common problem for the over-the-phone toxicologist!). In general, it is a terrible error to attribute a chronic ulcerative lesion to a spider bite because debilitating or potentially life-threatening conditions (that may be treatable) can be missed.

Worldwide, possible causes of lesions that may be attributed to spider bites include:

  • Infection
    • bacterial – e.g. staphylococal, streptococcal, gonococcal, syphilis, mycobacterial (e.g. M. ulcerans), Pseudomonas, Vibrio (e.g. wounds exposed to sea water), melioidosis, nocardia, anthrax, tularaemia, plague, Chromobacterium
    • fungal – e.g. Candida, sporotrichosis, Aspergillus
    • protozoal – e.g. leishmaniasis
    • ricketsial – eg. scrub typhus, Lyme disease
    • viral – e.g. herpes simplex, herpes zoster, orf
  • Neoplasia – e.g. squamous cell carcinoma, basal cell carcinoma, lymphoma
  • Trauma – e.g.accidental or factitious injury, chemical burns
  • Toxic epidermal necrolysis
  • Other:
    • Contact dermatitis
    • Diabetic ulcers
    • Eythema nodosum
    • Localised vasculitis
    • Lymphoid papillomatosis
    • Purpura fulminans
    • Pyoderma gangrenosum
    • Stevens–Johnson syndrome and erythema multiforme
    • Toxic epidermal necrolysis

Q5. Describe the appropriate investigation, management, and disposition of this patient.

Answer and interpretation

This man’s presentation is not consistent with a white-tail spider bite.

Further history and examination is essential to determine the diagnosis (consider the differentials in Q4) and appropriate management.

Investigations should be guided by the likely differential diagnoses. A skin biopsy (generally for skin lesions that have persisted for 3-4 weeks) and microbiological investigations (e.g. ulcer swabs) may be required.

Until a specific diagnosis is made, symptomatic treatment (e.g. oral analgesia) and routine wound care are appropriate management.

The patient’s disposition might include discharge to the care of his general practitioner for follow up, or referral to a dermatologist or other specialist (e.g. infectious diseases) as appropriate.

Q6. What spiders cause necrotic arachnidism?

Answer and interpretation

Necrotic arachnidism is the term used to describe the syndrome of necrotic cutaneous ulceration resulting from a spider bite.

The brown recluse, or fiddleback, spider (Loxosceles reclusa) is a known cause of necrotising arachnidism (in this case called ‘loxoscelism’). In southern Brazil, loxoscelism is considered a serious public health problem, with 3000 annual reports of loxosceles bites. However, loxoscelism is rare even where brown recluse spiders are an abundant native species and peoples’ homes support large populations of the spiders. Treatment options for loxoscelism are diverse and controversial. A conservative approach is often all that is required because the condition is often self-limiting.

Other spiders that have been reported to cause necrosis include:

  • hobo spiders (Tegenaria agrestis) – northwestern United States
  • yellow sac spiders (Cheiracanthium species) – worldwide
  • wolf spiders (Lycosidae family) – worldwide
  • crab spiders (Sicarius testaceus and S. albospinosus) – South Africa
  • black house spiders (Badumna species) – Australia

The jury is still out on the importance of many of these species in causing necrotic arachnidism. However, the bottom line is:

Attribution of spider bite as the cause of a necrotic or ulcerative skin lesion should be a diagnosis of last resort and must be supported by plausible findings on history, examination and investigation. Despite the prevailing worldwide mythology, necrotic arachnidism is a very rare condition.

  • Isbister GK, Gray MR. White-tail spider bite: a prospective study of 130 definite bites by Lampona species. Med J Aust. 2003 Aug 18;179(4):199-202. [PMID 12914510]
  • Hensley J. Brown recluse bites. EBM Gone Wild
  • Hensley J. Mediterranean recluse bite necroses cartilage. EBM Gone Wild
  • Bennett RG, Vetter RS. An approach to spider bites. Erroneous attribution of dermonecrotic lesions to brown recluse or hobo spider bites in Canada. Can Fam Physician. 2004 Aug;50:1098-101. PMID: 15455808
  • Swanson DL, Vetter RS. Bites of brown recluse spiders and suspected necrotic arachnidism. N Engl J Med. 2005 Feb 17;352(7):700-7. PMID: 15716564
  • White J. Debunking spider bite myths. Med J Aust. 2003; 179 (4): 180-181. PMID: 12914504

A balanced view on the White-tailed spider controversy from ABC’s Catalyst.


Toxicology Conundrum

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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