Opportunistic Monitor Lizards in the City
When I first encountered a monitor lizard in Singapore, I’ll admit I was genuinely frightened. Over time, that initial fear turned into genuine fascination. Their gentle demeanor, impressive urban adaptation, and significance in the human-animal stories of Singapore won me over.
To be close to wild predators of this size makes one feel particularly privileged to visit a city like Singapore, where greening initiatives and public awareness allow humans and wildlife to coexist in close proximity. Singapore is home to three native species of monitor lizards: the common Asian Water Monitor (Varanus salvator), the Clouded Monitor (Varanus nebulosus), and the rarer Dumeril's Monitor (Varanus dumerilii). The focus of today’s episode and post is Asian Water Monitor, as it is the species one is most likely to encounter in the city.
Close Urban Encounters
I’ve had my fair share of close encounters with monitor lizards in Singapore. I remember strolling through the Singapore Botanic Garden, when I suddenly spotted what looked like a small dinosaur just a few meters off the path. I was close enough to see the yellow speckles along his scaly back and the leathery texture of his flicking tongue. This lizard felt enormous. They can grow up to three meters long, so it is no wonder that many mistake them for crocodiles.
Another time, I nearly stepped on one who I'd mistaken for a tree root until he suddenly bolted away. I’ll admit I jumped and screamed. In another instance, at the Sungei Buloh Wetland Reserve, I watched two monitor lizards locked in what looked like a long, tight hug. Nearby onlookers explained that the two males were actually fighting for dominance, attempting to flip the other over. The brawl ended with the “hug” breaking in dramatic thrashing and splashing in the water, again, just a few meters away from the elevated boardwalk where I stood.
In Singapore, you might spot a monitor lizard at a HDB housing block, in a drain, or even at a rail station. Local news stories occasionally highlight monitor lizards wandering onto balconies and into residential buildings, but fortunately, these moments are often used as opportunities for public education rather than eradication campaigns. One example is a news story Mr Kalai Vanan, saying:
“There are no reasons to be concerned. As we green our city more, such occurrences will be more frequent as wild animals can adapt and find food in HDB estates.” - Mr Kalai Vanan, Co-Chief Executive Officer, ACRES (Animal Concerns Research and Education Society)
That monitor lizards are now a familiar presence near waterways, and that most Singaporeans calmly coexist with them, is a testament to the city’s commitment to coexistence with its wild inhabitants. It is also an indicator that these animals are often never far from natural habitats, like the Bishan-Ang Mo Kio Park.
Bishan-Ang Mo Kio Park as a Refuge and Multispecies Commons
The Bishan-Ang Mo Kio Park was initiated in 2006 by Singapore’s National Parks Board, or NParks, and the national water agency, PUB, the project was part of a regional effort called ABC Waters, short for “Active, Beautiful, Clean Waters.” The goal was to transform Singapore’s water bodies beyond their basic functions of drainage and water supply. In the project, the Kallang River was converted from a concrete canal into a meandering, naturalized river. The project increased storm water capacity while creating valuable community space for the nearby residents. The re-naturalized river’s floodplain doubles as 62 hectares of public park space, offering trails, river crossings, playgrounds, and look-out spots with seating. Since the park’s completion, biodiversity has increased by 30%, without introducing a single new species.
The park offers pretty much everything a monitor lizard could ask for–a clean, flowing river for swimming and navigating, rotten logs for laying eggs, riverbanks for burrowing, and plenty of food animals who also thrive in this unique urban refuge. The park is a true multispecies commons in the heart of a dense urban residential neighborhood, where humans and wild animals shape the use and ecology of the park and its surroundings.
Masters of Global and Local Adaptation
The monitor lizard family is incredibly diverse, with species adapted to a wide range of habitats from aquatic to forest habitats. Members of the monitor lizard family are found in Africa, Asia, and Oceania, although nonnative monitor lizards now exist in the Americas, such as the Nile monitors in Florida. There are almost 50 total species of monitor lizards worldwide, with 27 of them living in Australia alone.
The Asian Water Monitor species is found across South and Southeast Asia, and they’ve made Singapore their own, using the city’s extensive network of canals and waterways to move, hunt, and navigate. They’re among the island’s largest terrestrial predators alongside pythons and wild boars, and they’re the second largest aquatic predator following the saltwater crocodile. These lizards will eat pretty much anything, feeding on insects, birds, crabs, snakes, fish, even juvenile crocodiles. Citizen-science observations in Singapore show that they hunt and scavenge in the morning and afternoon, spending the rest of the day basking and floating. When hunting in water, the Asian Water Monitor can remain submerged for up to 30 minutes. Asian Water Monitors are powerful swimmers, using their muscular tails to help propel while tucking their legs close to their bodies. They are such great swimmers that scientists believe they have made sea crossings. Following the catastrophic eruption at the Krakatoa islands of Indonesia in 1883, which wiped out all animal and plant life on the islands, monitor lizards were among the first animals to colonize the islands, by literally swimming there across the sea. In addition to being highly skilled swimmers, they are also architects.
Burrow Architects and Ecosystem Engineers
Asian Water Monitors excavate burrows for refuge from predators and nighttime shelter. These burrows can be found in a range of conditions: in river banks, on level ground, and in grassy slopes. A burrow can be surprisingly complex–up to 14 meters long, up to 2.4 meters deep, with multiple branches that lead into side chambers. Some are even large enough for a human to lie inside.
Reptiles rarely feature as ecosystem engineers, but monitor lizards certainly have something to prove. Their burrows are not just homes for monitor lizards, they’re gifts to the entire ecosystem: they aerate the soil, help circulate water, redistribute nutrients, and, once abandoned, provide critical shelter and breeding sites for other animals like frogs, snakes, and small mammals.
As scavengers, monitor lizards also play an important role in the ecosystem. Their strong stomach acid allows them to digest practically anything, including dead animals and human food waste. They contribute to nutrient cycling and biomass breakdown in forests, mangroves and urban spaces. In rare cases, Asian Water Monitors have taken their scavenging to the next level by digging up human corpses. This behavior was studied in Sri Lanka and also famously associated with Komodo dragons. As large predators and scavengers, Monitor Lizards may seem out of place in cities, but in Singapore, they are very much at home. In a nation of over six million people with limited land, Singapore has no room to draw clear boundaries between “urban” and “wild.”
Threats to Coexistence?
In Singapore, fortunately, it is illegal under the Wildlife Act to remove wild animals, including monitor lizards, from the wild. However, Asian Water Monitors face serious threats from the global reptile leather industry, traditional medicine markets, and habitat loss. The Asian Water Monitor is the most heavily traded lizard globally, and most of this skin harvesting occurs in Indonesia, which documents about 450,000 legally exported skins a year, but with illegal wildlife trafficking, the actual number of skins may be exponentially more. Singapore is a major importer of reptile skins and is a major trade hub for South Asia, so despite the country’s Wildlife Act, illegal trafficking may still occur under authorities’ notice. NParks takes illegal wildlife trafficking seriously, conducting raids, seizing illegal products, and monitoring online trade facilitated through social media platforms like Telegram.
Despite their ecological importance, monitor lizards across the world face growing threats, from habitat loss to industries that commodify their bodies. Monitor lizards are often overlooked, despite their large size and numbers, as they lack the cultural charisma we tend to reserve for more celebrated or charismatic wildlife of tropical Singapore. Yet their story tells us so much about urban coexistence, particularly with wild predators. How animals adapt and shape cities, how cities are pertinent for ecological thriving, and how policy influences who gets to survive. By paying attention to the Asian Water Monitor, we’re paying attention to how Singapore chooses to live with wildlife.
Of interest:
Rebecca Shen a landscape designer, artist, and animal activist. She is inspired by design to advance interspecies justice and imagine more anti-speciesist spaces. Rebecca graduated with a Master in Landscape Architecture at Harvard Graduate School of Design in 2023. There, she completed her design thesis, Sanctuary State: California’s Cowscape in Transition, which envisions the transformation of an 800-acre industrial cattle feedlot into a cow sanctuary in the San Joaquin Valley. Rebecca contributes as an assistant content creator for the show.
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