If you have turned on the porch light on a warm summer evening and found a long, slender snake with oversized eyes peering down from the rafters or sliding along a fence line, you have almost certainly met a brown tree snake. It's one of the most distinctive snakes in the Sydney region, and the one most likely to turn up inside a home, shed or roof space rather than out in the open.
At Sydney Snake Catcher we get regular calls about brown tree snakes through the warmer months, especially after rain. They're excellent climbers, fearless around urban structures, and one of the few local species that will genuinely come into a house through a gap that most other snakes would walk straight past. The first thing every homeowner should know is that while this species is technically venomous, it is not considered dangerous to humans.
The brown tree snake, Boiga irregularis, is a rear fanged colubrid native to northern and eastern Australia, and also found in parts of Indonesia, Papua New Guinea and the Solomon Islands. It's infamous internationally as the species that devastated Guam's native bird population after being accidentally introduced there in the 1940s, but within its native Australian range it's simply one part of a functioning ecosystem.
Venom rating: mildly venomous, not considered dangerous to humans Total length: around 1.2 metres average, up to 2 metres Conservation status: IUCN least concern Urban adaptation: very high Activity: strictly nocturnal, most active in the warmer months
Brown tree snakes have a very distinctive look once you know what to search for:
Slender bodied with a notably long, thin profile Head clearly distinct from the neck Very large eyes with vertical pupils, an adaptation for hunting at night Body colour ranging from reddish brown through tan to pale brown Irregular darker crossbands or saddle markings along the back Cream to yellow underbelly Long, prehensile tail used for climbing Smooth scales with a slight gloss
The slender body, oversized eyes with vertical pupils, and clearly defined head are unmistakable together. No other Sydney snake has eyes that large relative to its head, and it's the single most reliable feature to check.
Eastern brown snake: round pupils, a much shorter tail relative to body length, faster ground movement, different head shape. Eastern browns are active by day and rarely climb. Diamond python: heavier built, distinctive diamond pattern with cream centres, round pupils, a much larger jaw structure. Green tree snake: round pupils, generally green or olive colouring, active during the day rather than at night.
The vertical pupils and oversized eyes are the giveaway. A slender snake climbing a fence at night with eyes that look almost too big for its head is almost certainly a brown tree snake.
Brown tree snakes are highly adaptable and occupy a wide range of habitats. In the Sydney region they do particularly well anywhere vegetation meets built structure.
Natural habitats include open woodland and dry sclerophyll forest, rainforest margins, coastal scrub, sandstone country, and riparian vegetation along creeks and rivers.
In urban settings they turn up in roof spaces and ceiling cavities, garden sheds and garages, aviaries and chicken coops, pergolas, verandahs and external rafters, mature gardens with trees and shrubs, brick walls with deep mortar gaps, stone retaining walls, and stacked timber.
The combination of strong climbing ability and nocturnal habits means this species reaches urban structures that ground dwelling snakes never do. A brown tree snake can scale a brick wall, slip through a gap under a roof tile, and spend the day curled up in a ceiling cavity without the homeowner ever knowing it's there.
The brown tree snake is one of the most accomplished climbers in the Australian snake fauna. The prehensile tail works almost like a fifth limb, gripping branches, beams and structural edges while the body reaches forward. They can climb almost any vertical surface that offers grip, brick, bark, mesh, rough timber, and even some painted surfaces.
Their hunting style suits this lifestyle. They're ambush predators that move through vegetation at night, investigating roosting birds, sleeping lizards and the entrances to tree hollows. The large eyes give excellent low light vision, letting them hunt in conditions where most other snakes are effectively blind.
When threatened, typical behaviour includes flattening the body to look larger, raising the head and forebody, striking repeatedly with the mouth open, hissing, and coiling defensively into a tight S shape. The display is impressive and can be alarming to watch, but the bites themselves are rarely a real threat to a person.
This is where brown tree snakes generate the most calls. They're notorious nest raiders, and a backyard aviary or chicken coop full of birds is essentially an open invitation. We regularly remove them from aviaries housing finches, budgies and other small birds, chicken coops where they take eggs and chicks, roof cavities directly above bedrooms, garages and sheds with mouse populations, pergola rafters above outdoor dining areas, and external lights where geckos and moths gather.
If you find one in an enclosed space, particularly an aviary or a roof cavity, call a licensed reptile catcher. They aren't dangerous, but they aren't easy to remove either. They climb, they hide, they squeeze into tight gaps, and a homeowner attempting it themselves often ends up losing track of the snake inside the structure.
Brown tree snakes are mildly venomous. They have small fangs set toward the back of the upper jaw and produce a mild venom used to subdue prey. A bite to a person typically causes localised swelling around the site, mild pain, occasional itching or a rash, and no systemic effects in a healthy adult.
They are not considered dangerous to humans. The combination of small rear fangs, mild venom, and the difficulty this species has actually delivering venom into a human bite means confirmed bites usually produce little more than a bee sting equivalent.
Bites should still be treated properly. Wash the site with soap and water, apply a cold compress if there's swelling, and monitor for any unusual symptoms. Seek medical attention if swelling is significant or there's any sign of an allergic reaction, and children, elderly people or anyone with compromised immunity should see a doctor regardless.
There are no recorded human deaths from brown tree snake bites in Australia.
The risk to pets is more variable. Small birds in aviaries face real risk from both constriction and envenomation. Cats and dogs generally aren't at serious risk from a bite, though a smaller pet should still be monitored if bitten.
Brown tree snakes are opportunistic nocturnal predators. Diet includes birds, particularly roosting and nestling birds, bird eggs, lizards, especially geckos, frogs, small mammals such as mice, rats and small possums, and occasionally other snakes.
The willingness to raid nests is part of what makes this species so successful in suburbia. Wherever suburbs offer nesting sites, gardens, aviaries, eaves, palm trees, brown tree snakes have plenty to eat.
Mating occurs in spring and summer, with eggs laid across the same period. Clutches run from 3 to 12 soft shelled, leathery eggs, laid in moist, protected sites such as roof cavities, tree hollows, deep rock crevices and ceiling spaces. Hatchlings are fully independent from the moment they emerge.
The preference for warm, dry, protected nest sites is exactly why this species ends up in roof cavities so often. A female that finds a good one will keep using it.
The right response depends on where it is.
If it's outside, in the garden or on a fence, leave it alone. It's hunting and will move on by morning. Keep pets away and don't approach or try to capture it.
If it's inside, in a roof cavity or an enclosed structure, call a licensed reptile catcher. Sydney Snake Catcher handles this kind of removal routinely. Don't try to remove it yourself, since they climb and hide well enough that you'll likely lose track of it. Close the door to that room or space if you can, and keep children, pets and family clear of the area.
If it's in an aviary or chicken coop, remove birds and eggs from the immediate area if it's safe to do so, then call a licensed catcher. Once the snake is out, identify and seal the entry point, since brown tree snakes will return to a reliable food source.
Do not kill it. It's protected native wildlife. Do not corner it, since a cornered snake will defend itself, and while the bite isn't dangerous, it's still a bite. Do not write it off as just a tree snake and ignore it either, since a wrong identification can be an expensive mistake if it's actually inside an aviary.
Seal gaps in eaves, fascia boards and around roof tiles. Fit snake proof mesh to aviary doors and ventilation gaps, and use snake proof chicken coop mesh with an aperture under 12 millimetres. Clear dense vegetation from immediately around buildings and trim branches that overhang the roofline. Cut down food sources such as spilled bird seed, unsecured bins and exposed pet food, and deal with rodent problems, since mice and rats are a direct draw.
Are brown tree snakes dangerous to humans? No. They're mildly venomous but not considered dangerous. A bite typically causes localised swelling and mild pain, similar to a bee sting, with no recorded human deaths in Australia.
Why do brown tree snakes keep getting into my roof? They're strong climbers that hunt at night and look for warm, dry, protected spaces to shelter and breed. A roof cavity with an accessible gap is close to ideal.
Are brown tree snakes a risk to chickens or aviary birds? Yes. They're persistent nest raiders and will take eggs, chicks and small birds given the chance. This is the most common reason we're called about this species.
What should I do if I find one inside my house or shed? Close off the room if you can, keep children and pets away, and call a licensed catcher. Don't try to remove it yourself, since they climb and hide in ways that make DIY removal difficult.
The brown tree snake is one of Sydney's most distinctive species, a slender, nocturnal climber with oversized eyes that thrives in suburbia as readily as in the bush. It's mildly venomous but not dangerous to humans, with bites producing little more than localised swelling and discomfort. It is, however, a determined raider of aviaries, chicken coops and roof spaces, and removal from any enclosed structure should be handled by a licensed catcher. A brown tree snake in the garden is generally a sign the local ecosystem is intact enough to support a healthy population of birds, lizards and small mammals.
Found a brown tree snake or another reptile at your home? Sydney Snake Catcher operates 24/7 across the Greater Sydney region. We are fully licensed and insured, and we identify and safely manage any reptile you encounter. Call 1300 599 938.
The Brown Tree Snake (Boiga irregularis) is a nocturnal, rear-fanged snake found along Australia’s northern and eastern coasts. Growing to approximately 1.5 metres, it inhabits forests, grasslands, rocky outcrops and suburban areas, where it hunts birds, bats, lizards, rats and other small mammals.
Sydney Snake Catcher provides professional Brown Tree Snake removal and licensed reptile relocation across Sydney. Brown Tree Snakes are nocturnal and mildly venomous, and they should not be handled by untrained people. If a Brown Tree Snake is found inside a building or another unsuitable location, keep your distance, watch where it goes and call 1300 599 938 for assistance.
Brown Tree Snakes lay eggs in protected sites such as hollow logs and rock crevices. Although venomous, their rear-positioned fangs and relatively mild venom mean they are not generally considered dangerous to adults; however, every suspected snakebite should receive medical assessment.
