Like many other islands, Guam’s natural history traces two routes: 1) that of the flora and fauna that made their way to the island on their own and 2) that of those that were brought to the island by humans—either deliberately or accidentally. These two threads have intertwined during the ~4,000 years of human history on the island. Today, you can see the results in Guam’s ecosystem. 

Below, we’ll introduce you to 12 fascinating animals you might meet on Guam. Some are native to the island. Others are endemic, meaning you won’t find them anywhere else. And still others are invasive—introduced by human arrivals throughout the years. Even though these animals don’t “belong” on Guam, their impact was significant enough to include them on this list. We’ll also include a few animals from other islands in the Mariana Island chain, including Rota. 

First, let’s start with the most notorious animal on Guam: the brown tree snake. 

The Brown Tree Snake

Boiga irregularis

Sometime after World War II, the brown tree snake made its way to Guam, likely by hitching a ride on a boat. Because the snakes have no natural predators on Guam, they multiplied quickly. Brown tree snakes soon devastated the island, decimating its bird population and creating today’s “silent forests” on Guam. The snakes also climbed power lines and damaged electrical boxes, triggering numerous power outages.  

Efforts are underway to control the population, including massive drops of mice laced with Tylenol, which is toxic to the snakes. 

Fast Fact: Scientists recently discovered exactly why the brown tree snake has been so deadly for Guam’s forest bird population. The snake has a unique method for climbing trees and poles, called “lasso locomotion.” Check it out in the video below: 

Mariana Fruit Bat 

Pteropus mariannus 

Also known as the Mariana flying fox, fanihi in Chamorro, or “a delicacy” in many parts of Guam, the Mariana fruit bat feeds on the fruits and flowers around the island. As you can see from the picture above, they tend to roost in groups. Typhoons and predators have winnowed down the population, and Mariana fruit bats are considered “threatened” by the U.S. Fish and Wildlife Service.  

Archaeologists have unearthed evidence that the Chamorro people have been eating fruit bats for more than 1,000 years. In recent years, a scientific study linked eating fruit bats to a neurodegenerative disease, resulting from the buildup of a particular neurotoxin within the bats’ systems. Hunting these bats has been illegal since 1973 to protect the future bat population. 


Coconut Crab  

Birgus latro 

Like the Mariana fruit bat, ayuyu, or coconut crabs, are considered a delicacy. These crabs get their name from their favorite meal—coconuts. Believe it or not, their front claws are powerful enough to open a coconut shell, granting them access to the sweet meat inside. To protect the dwindling ayuyu population on Guam, coconut crabs must have a carapace of at least three inches wide to be eaten and at least four inches wide to be legally sold.  

Fast Fact: Coconut crabs are also known as “robber crabs.” They have been known to steal things from houses, and they got a reputation during World War II for grabbing items from soldiers. Coconut crabs can reach a leg span of three feet and a weight of more than nine pounds, so they’re capable of stealing more than you’d think!  

Mariana Monitor Lizard 

Varanus tsukamotoi 

Researchers originally believed that the hilitai was introduced to the Mariana Islands through human intervention. However, further study revealed that the ancestors of this large lizard made its way to the Mariana Islands during the late Pleistocene era—at least 11,700 years ago. (That’s more than 7,000 years before the documented arrivals of humans!) Although hilitai can grow as long as three to four feet, they generally don’t bother humans unless threatened.  

Fast Fact: The Mariana monitor lizard generally sticks to its jungle home. However, you might see them crossing the road or wandering around residential neighborhoods. 

Cane Toad 

Rhinella marina 


You’ll find cane toads in a number of warm places: Florida, Hawaii, Puerto Rico, Guam and the Northern Marianas. However, this amphibian is originally native to South and Central America. Cane toads have been deliberately released in many parts of the world with the intention of using them to control pests. Due to their ability to reproduce easily, their population can quickly get out of control. Additionally, their willingness to eat almost anything has caused significant damage to fragile ecosystems.  

Fast Fact: Cane toads also secrete a venom that’s poisonous to dogs, so keep an eye out if you’ve got a dog or another pet that spends time outdoors. It’s also believed that cane toads have contributed to the decline in population of the Mariana monitor lizard 

Mariana Eight-Spot Butterfly 

Hypolimnas octocula marianensis 

Believe it or not, this ababang, also known as the Mariana eight-spot butterfly, was the recent subject of a lawsuit against the U.S. Fish and Wildlife Service, filed by the Center for Biological Diversity and Blue Ocean Law. The Mariana eight-spot butterfly, along with 22 other species, were deemed threatened or endangered by the agency. However, the Fish and Wildlife Service failed to set aside a critical habitat to protect them, as required by the Endangered Species Act. According to the Center, the Mariana eight-spot butterfly is under threat from invasive species, development, military training, urbanization, typhoons, and climate change. The butterfly feeds only on two native plants. Thanks to the lawsuit, a habitat will be secured for them going forward so they can thrive. 

Carabao: Water Buffalo 

Bubalus bubalis 

Many consider the carabao/karabao the unofficial animal of Guam. In fact, the carabao is such an important symbol on Guam that they were the subject of the recent “Carabaos on Vacation” campaign, introduced by the Guam Chamber of Commerce Tourism Committee. Businesses and organizations all over Guam bought fiberglass carabao statues and painted them, placing them around the island. 

Carabaos were brought to Guam from the Philippines to assist with farming during the Spanish occupation. They quickly became the quintessential animal of that era. Carabaos pulled carts and plowed fields. Today, many associate carabaos with the quieter days of Guam, when agriculture dominated the island. 

Fast Fact: Much like deer, wild pigs, and feral pigs, Guam residents are allowed to domesticate carabaos and raise them as livestock. However, it’s illegal to hunt or kill feral carabaos. 

Guam Tree Snail 

Partula radiolata 

The Guam tree snail and its intricately detailed shell are endemic to Guam’s forests. Like the fat Guam partula (Partula gibba), the Guam tree snail prefers the shady forest. However, recently, this tree snail was responsible for the delay of the construction of Simon Sanchez High School, when a colony of snails were discovered at the build site. Whether they will modify their design to accommodate the snails or relocate the population is yet to be determined. Either way, these endangered beauties are worth protecting, wouldn’t you agree? 

Feral Chickens 

You’ll find feral chickens all over Guam. By some reports, the population is only growing. While some look at the island’s feral chicken population and see a nuisance, others see the potential for food, both in terms of meat and eggs.  

Currently, it’s illegal to take wild chickens since Guam law protects all wild birds and their eggs—with the exception of black drongos, domestic pigeons, the black-headed manikin, and the European tree sparrow. Changing the law would offer recourse for those who see feral chickens as a nuisance in their neighborhoods. It also could offer a novel food source on Guam, while giving new meaning to the term “free-range chicken.” 


Three Birds Endemic to Guam and the Marianas 

It only felt fitting to follow the write-up of the brown tree snake with a few notes on the bird populations it’s impacted. Specifically, we’ll highlight three endemic birds. These three have only ever been found on Guam—or within the Mariana Island chain. 

Rota White-Eye

Zosterops rotensis 

These colorful forest birds, called nosa Luta in Chamorro, are endemic to the island of Rota. Their name comes from the white ring of feathers you’ll see around their eyes, creating a stark contrast with their greenish body and yellow belly feathers.  

Curious what the Rota white-eye looks like? You can see an illustration of the Rota white-eye in this poster from the Guam Division of Aquatic and Wildlife Resources and the Division of Fish and Wildlife of the Commonwealth of the Northern Mariana islands. 

Fast Fact: These birds prefer higher elevations—above 400 feet. 

The Guam Rail

Hypotaenidia owstoni 

This flightless bird is a rare success story. Thanks in large to the brown tree snake, Guam rails went extinct in the wild—a tragedy for the official territorial bird of Guam, which is known as the ko’ko’ in Chamorro. After capturing 21 birds, scientists were able to breed them in captivity, then release them on Cocos Island and Rota. They’ve been successfully breeding in the wild, making the Guam rail only the second bird in history to go from extinct in the wild to critically endangered. (The California condor is the other.) 

Guam Kingfisher

Todiramphus cinnamominus 

Like the Guam rail, the Guam kingfisher faced extinction and is currently only found in captivity. Scientists are currently working on reintroducing the sihek to the wild. Because the brown tree snake population is still not under control on Guam, biologists are currently considering Palmyra Atoll for the birds’ release.  

Fast Fact: The Guam kingfisher is very territorial. In captivity, they must be kept in separate enclosures—or even separate buildings—unless they’re breeding.  

Want to know more about the native birds of Guam? Check out this series of illustrations by artist H. Douglas Pratt, commissioned by the Guam Division of Aquatic and Wildlife Resources: 

Exploring All That Guam Has to Offer 

One of Guam’s most compelling features is its natural beauty—its beaches, its forests, its mountains, its rivers—and all the creatures that live in these diverse ecosystems. This list offers just a taste of the interesting animals you’ll find on Guam. Have fun exploring!

Considering a move to Guam? Our Tamuning-based team would be happy to help you make a safe, easy, and affordable move so you can explore all that Guam has to offer. Just reach out for a free quote to get started 

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