Earless Monitor Lizard

The endangered earless monitor lizard, found only on the island of Borneo, is now threatened by illegal pet trading. Few animals are as elusive as the endangered earless monitor lizard, native only to the northwestern coastal region of the island of Borneo.

This small and unique lizard was first described in 1878 by Franz Steindachner. The bumpy little reptile with a long tail and no external signs of ear parts was named Lanthanotus borneensis, an apt descriptor that roughly translates to “hidden ear from Borneo.”

More than 20 years passed before another specimen was presented in Europe. The new specimen was presented by George A. Boulenger at the 1899 meeting of the Zoological Society of London. Over the next several decades, scientists searched for live Lanthanotus borneensis specimens. They found fewer than a dozen individual specimens in nearly 100 years.

With each new discovery, they continued to debate this unique lizard’s taxonomy, comparing it with other known reptiles. They assigned it first to one family and then another before finally agreeing to leave it in a family of its own.

In recent years, despite being protected within the borders of the countries it calls home, the earless monitor has become a victim of illegal trade. More specimens have been harvested by illegal traders in just the last two decades than were found in the first 130 years since the lizard was discovered.

The International Union for Conservation of Nature (IUCN) listed the earless monitor lizard as endangered in 2019. The exact size and range of the native population are unknown. However, illegal poaching and habitat loss will almost surely have a detrimental effect on the future of this vulnerable species.    

Incredible Earless Monitor Lizard Facts

• The earless monitor lizard can remain motionless without the need for food or water for a very long time.
• The bumpy scales on an earless monitor cling to mud and help the lizard camouflage itself.
• In the first nearly 100 years after Lanthanotus borneensis was discovered, only about a dozen specimens were found.
• Earless monitor lizards do not have any external ear parts, but they can hear.
• The earless monitor is considered endangered, and its biggest threats are illegal trade and habitat loss.

Where to Find

Earless monitor lizards are native to only one place on the planet: the equatorial island of Borneo in the southwestern Pacific Ocean. Borneo, the third largest island in the world, is jointly claimed by three nations. Indonesia makes up the south while Malaysia holds the north and northwest.

The tiny nation of Brunei, which is surrounded by the Malaysian state of Sarawak, claimed independence in 1984. The lizard is a protected species in all three nations.

Borneo is covered in a rich and thriving rainforest, featuring rivers and mountains. The island is home to many unique species of plants and animals, including the Malayan tiger, orangutans, king cobras, and the clouded leopard.

The range of the earless monitor lizard has been limited to northwestern Borneo. Now, because of deforestation and habitat loss, the species is thought to be found only around the Niah National Park.  

Evolution and Origins

The earless monitor lizard is native to the island of Borneo in Southeast Asia and is specifically found in Sarawak, East Malaysia, as well as West and North Kalimantan, Indonesia, making it an endemic species to the region.

The earless monitor (L. borneensis), an uncommon and lesser-known lizard species originating from Borneo, stands as the sole member of the subfamily Lanthanotinae. Possessing an elongated body and a relatively long neck, this species exhibits small limbs and reaches a maximum length of 40 cm (16 inches).

Having originated over 90 million years ago in northern Asia, monitor lizards (Varanidae) underwent expansion during the Miocene era, spreading across Europe, Africa, and Australia.

This diverse group comprises 46 species and encompasses the largest lizards found in Africa, Asia, and Australia, while remaining absent from the Neotropical regions.

Scientific Name

The earless monitor lizard’s scientific name is Lanthanotus borneensis or sometimes noted as Lanthanotus borneensis Steindachner, 1878. Early texts also use the spelling Lanthonotus borneensis.

“Lanthanotus” means hidden ear, while “borneensis” refers to Borneo, the island where the lizard is found.

Scientists have long debated the taxonomy of the earless monitor lizard. Because its features were so unique, Steindachner in 1878 listed the earless monitor lizard in its own family, Lanthanotidae.

In 1899, when the second specimen was introduced to the Zoological Society of London, Boulenger argued against that designation. He claimed that the earless monitor lizard shared enough similarities that it should be included in the family Helodermatidae.

That family includes beaded lizards and the Gila monster, which is native to Mexico and the southwestern United States. Scientists at the time carefully studied the specimen and, comparing its anatomy to other known species, did agree with Boulenger’s conclusion.

By the 1960s, a few more specimens had been found and studied. Although the similarities to the members of the Helodermatidae family were clear, and it was apparent that the lizards shared a common but distant ancestry, there were also differences significant enough to place the earless monitor lizard back in a family of its own. Today, it remains the single species in the family Lanthanotidae.

Different Types

• Savannah monitor
• Varanus timorensis
• Dumeril’s monitor
• Short-tailed pygmy monitor
• Pygmy Mulga Monitor
• Mertens’ water monitor
• Blue Spotted Tree Monitor
• Pilbara rock monitor
• Dampier Peninsula monitor
• Stripe-tailed goanna

Appearance

When you think of monitor lizards, you probably think of big, hulking giants like the Komodo dragon, which can easily grow to more than 8 feet in length and weigh between 200 and 300 pounds. Monitor lizards can vary greatly in size, though, and the earless monitor lizard is quite small. It averages only about 16 inches in total length and reaches a weight of approximately 2 to 4 ounces.

These lizards are dark, solid orange-brown in color, with a lighter underside. The lizards do exhibit signs of sexual dimorphism, with males noticeably larger around the base of the tail and having wider heads. Males are also a bit larger than females on average.

As the name suggests, the earless monitor lizard has no visible external ear parts. It can, however, still hear.

Similarity to Beaded Lizards

The bumpy, nodular appearance of the earless monitor lizard is the result of heavily keeled scales. These scales create a surface that holds well to mud, allowing the lizard to camouflage itself easily.

With its bumpy appearance, the earless monitor is so similar in appearance to the more familiar beaded lizards and the Gila monster that it was placed in the same family for a while, but further research indicated that although they shared a distant ancestor, they were different enough to be in families of their own.

Other Physical Characteristics

The earless monitor lizard has tiny legs, and the front legs especially are hardly substantial enough to support its stout neck and head. It has a long tail perfect for swimming and a snout made for digging in the soil. Its movements on land have been observed to be similar to that of a snake, while in the water it is a fast and adept predator.  

Notable differences in the teeth and jaws of the earless monitor differentiate it from other monitor lizards of the Varanidae family. Also, the earless monitor has recently been found to have venom, the protein-cleaving kallikrein enzyme, in its mandibular glands.

Behavior

In nearly a century, from the time the earless monitor lizard was first documented in 1877 and officially described in 1878, only a handful of specimens were collected from the wild. By the beginning of 1961, only 10 live specimens had been caught and studied. None of those had been found in recent years, despite concentrated efforts.

For many years scientists had been looking for the elusive earless monitor lizard all across the western section of the island of Borneo. Unfortunately, they had consistently come up empty-handed. When a new individual was found at a research center near the Great Caves of Niah, scientists were understandably excited.

At last, researchers were able to study and record the behaviors of a live specimen. For three months they kept watch over the lizard day and night, making notes and even filming its behaviors until the creature died. The team, led by Tom Harrisson and N.S. Haile published their report in the Journal of the Ohio Herpetological Society.

Hide and Seek

One of the reasons the earless monitor lizard has been so successful in evading detection is that it is nocturnal. The live specimen that Harrisson and Haile studied only came out at night, and only for a short time. In the wild, these lizards have been noted to emerge in the late evening to hunt, often catching prey in shallow streams or in the soil.  

When not searching for food, this extremely stealthy lizard lies practically motionless. It buries itself in the soil with its bumpy scales holding a layer of dirt to camouflage its body.

The lizard is able to shut down its metabolism to such an extent that it appears comatose or nearly dead. It can go for long periods without food or water and with little need even for fresh air. Lethargic would be an apt term to describe the lifestyle of the earless monitor when it is not on the hunt.

Diet

Data on the diet of earless monitor lizards in the wild is limited. Much of what is known is based on evidence of their stomach contents, either from regurgitation or from examination of deceased specimens. A favorite food of this predatory lizard appears to be crustaceans, which they catch in the lowland streams within their habitat. They are adept swimmers and are able to catch crustaceans, small fish, and frogs in the water.

In captivity, the earless monitor has been noted to eat eggs, frog meat, crustaceans, and other bits of meat. Feeding behavior in captivity has been observed, with individuals feeding on small frogs both on the surface of muddy soil and underwater.  

Reproduction

Little is known about the reproductive habits of earless monitor lizards in the wild because they are so difficult to find and observe. However, these lizards have been studied in captivity in recent years. Successful breeding has taken place and details have been recorded.

We now know that it takes more than six months from the time of fertilization for earless monitor lizards to hatch. This length of time includes a gestation period of approximately 130 days, as observed by German naturalist and reptile expert, Manfred Reisinger in 2015. Reisinger documented the mating behavior of a captive pair of earless monitors. He noted that the female laid her eggs 131 days after the first recorded mating session.

Following gestation, females of the species will deposit a clutch of about 4 to 6 eggs. Incubation then takes between 70 to 80 days.

Captive breeding is occurring, but among collectors who may have obtained illegally caught specimens which were then trafficked around the world. Therefore, currently, little more is known or has been published regarding the development of juvenile earless monitor lizards. Very little is known about their age at maturity, or other details regarding their life cycle.

Threats to Survival

The earless monitor lizard has been listed as endangered since 2019, and it is protected within the nations that comprise its habitat in Borneo. However, native populations are still being negatively affected by illegal trade. Since 2012, live specimens have been traded at an increasing rate. Individual specimens are currently being sold around the world for up to several thousand dollars each.

Failure of the Convention on International Trade in Endangered Species to immediately add the earless monitor lizard to the CITES Appendix III, giving it interim protection from international trade while it was considered for permanent protection, was likely the reason for the skyrocketing trade of the species. Collectors rushed to get this “holy grail” of lizard species at whatever price before the window was closed on poaching.

Additional threats to the earless monitor lizard come from deforestation and habitat loss. As the available habitat shrinks, the known subpopulations have begun to disappear. Currently, most live specimens are found around the Niah National Park.

What is the Lifespan of the Earless Monitor Lizard?

Due to the elusive nature of the earless monitor, little is known about the average life span of the species in the wild.