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Boiga irregularis
General Details, Taxonomy and Biology, Venom, Clinical Effects, Treatment, First Aid , Antivenoms
Boiga irregularis  ( Brown Cat Snake )  [ Original photo copyright © Dr Julian White ]
Family: Colubridae
Subfamily: Colubrinae
Genus: Boiga
Species: irregularis
Common Names
Brown Cat Snake , Eastern Brown Tree Snake , Brown Tree Snake
Australia + New Guinea + Indonesia
Australia, Indonesia, Papua New Guinea, Solomon Islands, Guam
Taxonomy and Biology
Adult Length: 1.40 m
General Shape
Large in length, slender ( except the very large almost python like physique of Guam specimens ), laterally compressed body with elongate tail. Can grow to a maximum of about 2.0 metres in Australia, 2.3 metres in New Guinea and over 3.0 metres in Guam. Head is subovate, broad and very distinct from neck. Eyes are very large in size and prominent with vertical elliptical pupils. Dorsal scales are smooth. Vertebral scale row is enlarged. Ventral scales have a sharp ridge either side resulting in an arch-like cross-section which enhances its climbing ability.
Found in a wide range of habitats varying from rainforest and mangroves to both wet and dry sclerophyll forests and coastal heaths in both Australia and New Guinea, found also in montane forest ( up to about 1400 meters ) and cultivated gardens and near human village settlements in New Guinea. It has thrived on the small island habitat of Guam.
Nocturnal ( or crepuscular ) and arboreal, but frequently forages for food on the ground. Tends to take shelter in tree hollows or fallen logs, caves or crevices and very occasionally under stones. A very aggressive snake if disturbed or provoked. It throws its forebody into a series of S-shaped loops and strikes swiftly, accurately and savagely often with the mouth agape.
Feeds mainly on small mammals, birds, their chicks and eggs, small lizards ( and their eggs ) and occasionally small snakes. On Guam, this species has had a devastating effect on the native ground nesting and flightless bird populations.
Species Map
Small (Approx 20k) version
Average Venom Qty
6.7 mg ( n= 19, dry weight ), Weinstein et al (1991) ( Ref : R000660 ).

2.3 to 10.8 mg ( dry weight ), Chiszar et al (1992) ( Ref : R000661 ).

Guam :
Specimens 1 metre : 0.642 ± 0.593 mg ( dry weight ), Vest et al (1991 ) ( Ref : R000663 ).

Specimens > 1 metre : 6.888 ± 4.929 mg ( dry weight ), Vest et al (1991 ) ( Ref : R000663 ).
General: Venom Neurotoxins
Possibly present
General: Venom Myotoxins
Not present
General: Venom Procoagulants
Not present
General: Venom Anticoagulants
Not present
General: Venom Haemorrhagins
Not present
General: Venom Nephrotoxins
Not present
General: Venom Cardiotoxins
Not present
General: Venom Necrotoxins
Not present
General: Venom Other
Not present
Clinical Effects
General: Dangerousness
Moderate envenoming possible but unlikely to prove lethal
General: Rate of Envenoming: Unknown but likely to be moderate
General: Untreated Lethality Rate: Unlikely to prove lethal
General: Local Effects
Mild to moderate local effects possible
General: Local Necrosis
Not likely to occur
General: General Systemic Effects
Variable non-specific effects which may include headache, nausea, vomiting, abdominal pain, diarrhoea, dizziness, collapse or convulsions
General: Neurotoxic Paralysis
Unlikely to occur
General: Myotoxicity
Does not occur, based on current clinical evidence
General: Coagulopathy & Haemorrhages
Does not occur, based on current clinical evidence
General: Renal Damage
Does not occur, based on current clinical evidence
General: Cardiotoxicity
Does not occur, based on current clinical evidence
General: Other
Not likely to occur
First Aid
Description: First aid for bites by non-front-fanged colubroid snakes likely to cause either no effects or only mild local effects.
1. After ensuring the patient and onlookers have moved out of range of further strikes by the snake, the bitten person should be reassured and persuaded to lie down and remain still. Many will be terrified, fearing sudden death and, in this mood, they may behave irrationally or even hysterically. The basis for reassurance is the fact that many venomous bites do not result in envenoming, the relatively slow progression to severe envenoming (hours following elapid bites, days following viper bites) and the effectiveness of modern medical treatment.
2. The bite wound should not be tampered with in any way. Wiping it once with a damp cloth to remove surface venom is unlikely to do much harm (or good) but the wound must not be massaged.
3. All rings or other jewellery on the bitten limb, especially on fingers, should be removed, as they may act as tourniquets if oedema develops.
4. The bitten limb should be immobilised as effectively as possible using an extemporised splint or sling.
5. If there is any impairment of vital functions, such as problems with respiration, airway, circulation, heart function, these must be supported as a priority. In particular, for bites causing flaccid paralysis, including respiratory paralysis, both airway and respiration may be impaired, requiring urgent and prolonged treatment, which may include the mouth to mask (mouth to mouth) technique of expired air transfer. Seek urgent medical attention.
6. Do not use Tourniquets, cut, suck or scarify the wound or apply chemicals or electric shock.
7. Avoid peroral intake, absolutely no alcohol. No sedatives outside hospital. If there will be considerable delay before reaching medical aid, measured in several hours to days, then give clear fluids by mouth to prevent dehydration.
8. If the offending snake has been killed it should be brought with the patient for identification (only relevant in areas where there are more than one naturally occurring venomous snake species), but be careful to avoid touching the head, as even a dead snake can envenom. No attempt should be made to pursue the snake into the undergrowth as this will risk further bites.
9. The snakebite victim should be transported as quickly and as passively as possible to the nearest place where they can be seen by a medically-trained person (health station, dispensary, clinic or hospital). The bitten limb must not be exercised as muscular contraction will promote systemic absorption of venom. If no motor vehicle or boat is available, the patient can be carried on a stretcher or hurdle, on the pillion or crossbar of a bicycle or on someone's back.
10. Most traditional, and many of the more recently fashionable, first aid measures are useless and potentially dangerous. These include local cauterization, incision, excision, amputation, suction by mouth, vacuum pump or syringe, combined incision and suction ("venom-ex" apparatus), injection or instillation of compounds such as potassium permanganate, phenol (carbolic soap) and trypsin, application of electric shocks or ice (cryotherapy), use of traditional herbal, folk and other remedies including the ingestion of emetic plant products and parts of the snake, multiple incisions, tattooing and so on.
Treatment Summary
Bites by this species are not expected to cause medically significant effects and the only risk, probably small, is local secondary infection. Patients presenting with bites by these snakes do not require medical attention, other than to check for infection and ensure tetanus immune status. Patients should be advised to return if local symptoms develop, suggesting secondary infection.
Key Diagnostic Features
Bites unlikely to cause more than mild to moderate local swelling & pain, occasionally local bruising, paresthesia/numbness, erythema or bleeding, but no necrosis and no systemic effects.
General Approach to Management
While most cases will be minor, not requiring admission, some cases will be more severe, requiring admission and treatment, so assess carefully before early discharge.
Antivenom Therapy
No antivenom available
No Antivenoms
Boiga irregularis ( Brown Cat Snake ) [ Original photo copyright © Dr Julian White ]
Larger version
Boiga irregularis ( Brown Cat Snake ) [ Original photo copyright © Dr Julian White ]
Larger version
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