Clinical Management

With spider bites, identification of the culprit is particularly difficult.

If the spider is not brought in for identification, then identification on the basis of the patient's description is highly questionable. If the spider is available for identification, it is possible in most cases to achieve a conclusive result if identification is performed by an expert.

Clinical data from the literature cannot be related to a conclusively identified species in many cases. The clinical information available comes from bites caused by various spider species, and it may be that the individual specimens were reliably identified, identified according to unclear criteria or not identified at all. Indirect criteria, such as a course of envenoming considered typical for a particular species of spider, and geographical criteria are often used to aid in identification.

The range of differential diagnoses is wide:

• Primary bacterial, fungal and parasitic cutaneous infections
• Vascular occlusive or venous disease
• Pyoderma gangrenosum
• Necrotizing fasciitis
• Neoplastic ulcers
• and many others

Isbister et al (2005a) addressed the problem of “skin ulcers of uncertain aetiology presenting as suspected spider bites” which is the majority of patients clinicians must deal with. 

“Approach to the investigation and diagnosis of necrotic skin ulcers of uncertain etiology presenting as suspected spider bites*

* Modified from Isbister and Whyte (2004).

A Establish whether or not there is a history of spider bite 

• Clear history of spider bite (better if spider is caught)
• Refer to information on definite spider bites
• No history of spider bite
• Investigation should focus on the clinical findings: ulcer or skin lesion
• Provisional diagnosis of a suspected spider bite is not helpful

B Clinical history and examination

• Important considerations
• Features suggestive of infection, malignant processes, or vasculitis
• Underlying disease processes: diabetes, vascular disease
• Environmental exposure: soil, chemical, infective
• Prescription medications
• History of minor trauma
• Specific historical information about the ulcer can assist in differentiating some conditions
• Painful or painless
• Duration and time of progression
• Preceding lesion

C Investigations

• Skin biopsy
• Microbiology: contact microbiology laboratory prior tocollecting specimens so that appropriate material and transport conditions are used for fungi,
• Histopathology
• Laboratory Investigations: may be important for underlying conditions (autoimmune conditions, vasculitis), including, but not be limited to
  • Biochemistry (including liver and renal function tests
  • Complete blood count and coagulation studies
  • Autoimmune screening tests, cryoglobulins
• Imaging
  • Chest radiograph
  • Colonoscopy
  • Vascular function studies of lower limbs

D Treatment

• Local wound management
• Treatment based on definite diagnosis or established pathology
• Investigation and treatment of underlying conditions may be important, (e.g., pyoderma gangrenosum or diabetes mellitus)

E Follow-up and monitoring

• The diagnosis may take weeks or months to be established so patients must have ongoing follow-up.
• Continuing management: coordinated with multiple specialties involved as necessary."

NEUROTOXIC ARANEISM 

Neurological effects (autonomic and somatic nervous systems) with cardiovascular and pulmonary effects secondary to autonomic nervous system effects.

Experimental and clinical observations suggest that the major systemic effects of envenoming are caused by endogenous catecholamines and acetylcholine, which are released in response to certain spider venoms. As these are transmitters in the sympathetic, parasympathetic and somatic nervous systems, the resulting clinical symptoms of envenoming are dealt with under neurological (neurotoxic) venom effects.

NECROTIC LOXOSCELISM

subdivided into

• Cutaneous loxoscelism
• Cutaneous-haemolytic loxoscelism

Consult

• Emergency flowchart: Spiders 
• Clinical flowchart: Spiders
• Biological features
• Clinical entries: Spiders

Early removal of compression bandage results in rapid clinical deterioration (Miller et al 2000).
It is imperative to apply pressure-immobilization as early as possible, ideally within 10 minutes after the bite. The bandage must remain in place until the envenomation syndrome has completely resolved. The first aid knowledge of the population is dangerously deficient (Miller et al 2000).

For spider bites the same applies as for e.g. snake bites.

If a pressure bandage / pad but, also, tight (arterial) tourniquets (see comment above) on the affected extremity has been applied, 

• they sould not be removed until systemic envenoming has been excluded: absence of non-specific systemic symptoms and normal results of laboratory investigations (Ireland et al. 2010, Isbister and Berling 2025)
  or
• after completion of antivenom administration (if available an indicated) in patients with systemic envenoming (Isbister etal. 2025).

• adverse outcomes have been observed in patients with tight pressure bandages left in place for many hours (Little 2023).
• all patients must be observed after removal of the bandage.

Inquire

• time of the bite,
• nausea, vomiting, abdominal pain.
• Bite
  • Local pain,
  • local redness, 
  • local swelling
  • necrotic soft issue

• Urticating hairs
  • Skin
    • irritation and rashes; itching of the skin that can persist for several months 
  • Eyes
    • irritation and redness.

Assess

• state of consciousness.

Measure

• blood pressure/pulse,
• breathing (respiratory rate),
• oxygen saturation (pulse oximeter).

Observe/investigate

• Bite
  • Local pain,
  • local redness, 
  • local swelling
  • necrotic soft issue
• Urticating hairs
  • Skin
    • urticaria, papular dermatitis; itching of the skin can persist for several months 
  • Eyes
    • Keratitis, conjunctivitis, iritis, chorioretinal scar
• Cholinergic effects
  • Vomiting; sweating; hypersalivation and hyperlacrimation.
  • Bradycardia, arterial hypotension, shock. 
  • Priapism.
• Adrenergic effects 
  • Tachycardia, arterial hypertension, myocardial failure, pulmonary oedema (cardiogenic + ?non-cardiogenic component), cardiac ischaemia, shock, arrhythmias.
• Neuromuscular dysfunction
  • Muscle fasciculations and spasms, local and generalised

• Record and measure
  
  • ECG,
  • Blood sugar,
  • Clotting / bleeding
  • Symptoms and signs of haemolysis

Cardiovacsulas effects

• Blood pressure, pulse
• ECG
• Chest X-ray
• Blood gas analysis
• Forced expiration test (peak expiratory flow)

Haematological effects (rarely in Loxosceles sp. envenoming: see 'Clinical entries: Spiders'

• Hb, Hct
• Clotting time
• PT/aPTT
• TT
• Fibrinogen
• FSP
• D-dimers
• Platelets

• blood film (schistocytes > 1% is diagnostic of microangiopathic haemolytic anaemia) (early and late haemolysis obeserved!)
• Free haemoglobin in the plasma and urine
• Haptoglobin

• Blood group/blood sample for cross-matching

Loxosceles sp.
Severe envenoming with necrosis (very rare) and time course of the development of the lesion
"The bite may be painless initially, but there is progressive local discomfort over the next 2-24 hours. Stinging or burning pain develops with local erythema, itching and indurated swelling. Between 12-72 hours post-bite, a painful, tender ischaemic lesion appears, the ‘red-white-and-blue’ sign, its outer ring coloured red (vasodilatation), white (vasoconstriction) and central blue (pre-necrotic cyanosis) with serous or haemorrhagic vesicles, or blisters. It may spread gravitationally. Over the next 3-7 days, a black necrotic eschar develops in 60% of cases, which sloughs in a few weeks, sometimes leaving a deep necrotic ulcer.” (Warrell 2023; see also Sams et al 2001a; Table IV Typical evolution of Loxosceles lesion)).

Cutaneous-haemolytic loxoscelism (rare)
Haemolysis appears to occur rapidly or with a long delay after the bite (24–72 h to 2–3 days) (de Souza et al 2008; DiPaola et al 2022; Futrell 1992; Laxton et al 2024; Lucas 1988; Wasserman and Anderson 1983–84; Rosen et al 2012). Acute renal failure (AKI) is less frequent and is associated with poor outcomes (Isbister and Fan 2011). AKI is infrequent and only occurred in cases manifesting massive haemolysis (de Souza et al 2008; Malaque et al 2011).

Symptomatic emergency medical treatment and antivenom treatment are complementary strategies.

Antivenom in those spider bites in which antivenom is avaibale, of proven value and indicated, it must be secured as early as possible while emergency medical treatment is running.

The aim of symptomatic emergency medical treatment is the rapid correction of critical parameters (fluid balance, blood pressure, oxygenation etc.) and the maintenance of vital functions (respiratory, cardiovascular).

Symptomatic measures help bridge the gap until specific treatment (antivenom) can be administered and starts being effective. If no antivenom is available or if the required effect is not achieved with antivenom, the goal is to employ symptomatic measures until such time as the venom naturally starts losing its activity.

The aim of antivenom treatment is neutralisation of the venom. The success of antivenom treatment depends on the quality of the antivenom, the specific properties of those venom components relevant to envenoming and the time point at which antivenom is administered (neurotoxic envenoming).

Indications see 'Clinical mangement', 'Antivenom' in 'Clinical entries: Spiders'

See also
Emergency flow chart: Spiders

Clinical Flowchart: Spiders

If the selected antivenom is not effective, 3 possible causes need to be considered

1. correct identification of the cause, but insufficient dose administered;
2. correct identification of the cause, but inadequate efficacy of the antivenom;
3. incorrect identification of the cause → revision of identification.

Assessment of the value of antivenom in the treatment of Atrax sp. and Hadronyche sp. envenoming

• Antivenom has decidedly transformed the treatment of Atrax sp. and Hadronyche sp. envenoming. According to the available study and case reports, antivenom dramatically reduces case fatality and mortality. The rate of adverse reactions appears to be very low.
• see also (Isbister et al. 2003a, Isbister and Fan 2011, Ryan et al. 2017). 

Assessment of the value of antivenom in the treatment of Latrodectus sp. envenoming

• The currently available results on the effectiveness of Latrodectus antivenoms provide contradictory results. (Isbister et al. 2003a, Isbister and Fan 2011, Ryan et al. 2017).

• New develoments need to be followed-up.

Assessment of the value of antivenom in the treatment of Loxosceles sp. envenoming

• Antivenom treatment has little significance due to the purely practical reason that most patients do not consult a doctor until >24 hours after the bite. According to experimental investigations, antivenom no longer has an effect on the necrotising process at this point in time (Futrell 1992, Lucas 1988).
• “Of all the evaluated interventions, antivenom showed the greatest therapeutic potential, but there are no adequately performed clinical experiments that may assure the efficacy of the different treatments in loxoscelic bites or lead to a greater consensus of which would be the ideal therapy for the treatment of loxoscelism.” (Pauli et al 2006).
• see also (Isbister et al. 2003a, Isbister and Fan 2011, Ryan et al. 2017).
• New develoments need to be followed-up. 

See 

• Antivenom treatment.

• Manufacturer instructions of antivenom applied.
• 'Clinical mangement', 'Antivenom' in 'Clinical entries: Spiders'  

Comprehensive ABCDE approach
ICRC Basic Emergency Care: approach to the acutely ill and injured (SAMPLE and ABCDE approach: first module)