Brown tree snake (Boiga irregularis)

19 Surprising Facts About Brown Tree Snakes

Spread the love

The brown tree snake is an infamous invasive species known for causing ecological damage and widespread power outages across Guam. However, there are many surprising facts about these reptiles that many people don’t know.


The brown tree snake (Boiga irregularis) is a rear-fanged colubrid that is native to northern and eastern coastal Australia, Papua New Guinea, and many islands in northwestern Melanesian1. They were likely introduced to Guam shortly after World War II from cargo ships.

Since then, brown tree snakes have become extremely problematic invasive species in Guam. They have caused the extirpation of 9 out of 11 native forest birds in Guam and thousands of power outages. Their impacts have been ecologically and economically disastrous.

However, there are some little-known and unexpected facts about these snakes. Here are 19 of the most surprising facts about brown tree snakes:

19 Surprising Brown Tree Snake Facts

  1. Brown tree snakes are mildly venomous. They have small, grooved fangs at the rear of their mouth through which they deliver a mild neurotoxic and myotoxic venom. Their venom is not dangerous to humans but helps them secure prey.
  2. They have heat-sensing pits. Brown tree snakes have infrared heat-sensing pits between their eyes and nostrils that help them locate endothermic prey such as birds and small mammals in the dark.
  3. Their scales are keeled. Unlike most colubrid snakes, brown tree snakes have keeled scales. These are scales that have a raised ridge down the center. This aids them in climbing trees and rough surfaces.
  4. They are incredible climbers. Brown tree snakes have a prehensile tail that grips branches combined with their keeled scales allows them to excel at climbing and life in the trees. They are even comfortable bridging substantial gaps between trees and structures.
  5. They can reach over 3 meters long. The average length is only 1-2 meters. However, they are capable of exceptional growth with some individuals recorded at over 3 meters long, making them the second longest venomous snake species behind king cobras.
  6. Their teeth point backward. Like many rear-fanged venomous colubrids, their teeth point backward to grip and hold prey rather than sinking into flesh like viper fangs. They are not easily visible unless the mouth is wide open.
  7. They are nocturnal hunters. Brown tree snakes are primarily nocturnal and use their heat-sensing pits to locate prey in the dark. However, they may become more diurnal in areas with low predation pressure.
  8. They can survive without food for months. Brown tree snakes are remarkably resilient. They have slow metabolic rates and digestive systems that allow them to survive long periods without food. There are records of brown tree snakes living over 12 months without eating in captivity.
  9. Females can reproduce through parthenogenesis. Parthenogenesis is a form of asexual reproduction where females produce offspring without mating. Brown tree snake females kept in isolation have been documented to produce viable offspring through this process indicating an evolutionary adaptation to colonize new areas rapidly.
  10. They are responsible for thousands of power outages. On Guam, brown tree snakes frequently climb onto electrical wires and infrastructure causing short circuits and widespread power outages that affect hospitals, businesses, and public services. The costs of these outages are enormous.
  11. Their skin secretions can cause allergic reactions. The skin secretions of brown tree snakes contain several allergens that can cause severe irritation, blistering rashes, and anaphylaxis in sensitive individuals. This makes handling them dangerous for some people.
  12. They can detect prey through smell. Brown tree snakes have an acute sense of smell using their forked tongue and vomeronasal organ to detect prey pheromones and odor trails from over 30 meters away. This allows them to hunt prey efficiently even in total darkness.
  13. They have few natural predators. In their native range brown tree snakes co-evolved with predators and competitors that keep their populations in check naturally. However, on Guam, they lack these natural population controls causing their numbers to skyrocket unhindered.
  14. Invasive populations have far higher densities. Brown tree snakes normally occur at densities below 100 per square kilometer in their native range. In contrast, they can reach densities over 3,000 per square kilometer on Guam – a 30-fold increase!
  15. They can cause cascading ecosystem effects. By preying on birds, lizards, and small mammals brown tree snakes have directly and indirectly caused the decline and extinction of numerous species on Guam. This has changed entire ecosystem dynamics.
  16. Their eradication is challenging. Several techniques have attempted to control brown tree snake spread and reduce populations including traps, toxicants, and biological control but eradication has remained elusive due to their cryptic nature, resilience, and high reproduction rate.
  17. They can deter colonially nesting birds. Brown tree snakes have caused a 90% decline in the Mariana crow population. Their predation on eggs and chicks makes it challenging for this and other colonially nesting species to successfully breed and recover their former numbers.
  18. Small snakes can take down large prey. Despite their slender build, even juvenile brown tree snakes are capable hunters taking down relatively giant prey like adult Micronesian starlings and Guam rails that outweighed them more than 50 times over.
  19. They can sense thermal radiation. Laboratory experiments have shown brown tree snakes can visually detect thermal radiation in patterns that mimic endothermic prey. This allows them to not just sense but also see heat coming from warm-blooded animals.


What are some surprising facts about brown tree snakes?

Brown tree snakes have heat-sensing pits between their eyes to locate prey, keeled scales to help them climb, a prehensile tail, and mild rear-fang venom. They can also reproduce through parthenogenesis and some individuals can reach over 3 meters long.

How did brown tree snakes get to Guam?

Brown tree snakes likely arrived in Guam shortly after WWII from cargo ships carrying military equipment. They were accidentally transported from their native range in Papua New Guinea and Northern Australia.

What kind of damage have brown tree snakes caused on Guam?

On Guam, brown tree snakes have caused the extinction of 9 out of 11 native forest birds. They climb on electrical wires and infrastructure, causing thousands of power outages that affect hospitals, businesses, and public services costing millions annually.

Why has brown tree snake eradication been so difficult?

Factors like their secretive nature, resilience to starvation, rapid reproduction through parthenogenesis, and lack of predators have made brown tree snake eradication extremely challenging. Techniques like traps, barriers, and toxicants have had limited success.

How do brown tree snakes locate prey and threats?

Brown tree snakes have extremely sensitive smell and vision. They use their forked tongue to detect prey odor trails and have heat-sensing pits to locate warm-blooded prey. Their eyes can detect faint thermal radiation patterns emitted by endotherms.


The brown tree snake has surprised scientists with their climbing agility, hardiness, flexible reproduction, ability to cause cascading ecosystem changes, and the challenges involved in controlling their spread. They continue to threaten native wildlife across the Pacific islands and cause millions in economic damages annually. Understanding more about these snakes can help manage invasive populations while conserving delicate island ecosystems.

The brown tree snake remains one of the most damaging and fascinating invasive species today. Their surprising traits and abilities never cease to amaze researchers and wildlife managers working to mitigate their impacts. With more research, hopefully solutions will be found to control brown tree snake populations while protecting native island biodiversity.

  1. []

Spread the love

Similar Posts