Species

Little File Snake: The Silent Predator

Harmless to humans but often mistaken for a venomous sea snake, the file snake lives mostly in brackish mangrove swamps

Text by: Gerry Martin

The tide is high amongst the dense and knotted network of mangrove roots in Bhitarkanika National Park. The teeming fish feed on the nutrient-rich waters coming in from the sea as it mixes with mud, the mangroves and the life it holds. If you’re a fish-eater, this is the place for you; little file snakes (Achrochordus granulatus) seem to know that. They’ve chosen a habitat that would deter most other species and have truly made it their home.

A male little file snake picks up the pheromones a female is releasing upstream with the flowing current. Because his tongue is forked more than most other snakes, it allows him to pick up scents from a wider area and helps him triangulate and figure out where the scent is coming from. These snakes can pick up and identify all kinds of smells with their tongues and Jacobson’s organs, even pure water. Smell is the most useful sense to this species considering the low visibility in mangrove swamp waters, especially at night when file snakes are active. The male snake reaches the female only to find that he needs to compete with three or four other males to mate. Being much smaller than the females, they wrap themselves around her and, without actively fighting each other, just keep trying to mate until one of them succeeds. Once the female stops producing the pheromones, the males will disperse again and continue with their lives foraging in crevices, along mangrove beds, and even travel out to sea for fish, snails, and crustaceans. This behaviour of actively searching for prey also differentiates males from females. Females are almost exclusively ambush predators, partially wrapped around some support like a mangrove root, waiting to pounce on an unwitting fish swimming nearby.

The little file snake is a denizen of brackish mangrove swamps and is even seen out in the open sea. Photo: Rahulratan Chauhan  Cover Photo: One aspect of the physiology of the little file snake, the absence of a small bony canal connecting the inner ear to the brain case, makes it different from all other known species of snakes. Cover Photo: Gaurav Patil The little file snake is a denizen of brackish mangrove swamps and is even seen out in the open sea. Photo: Rahulratan Chauhan  Cover Photo: One aspect of the physiology of the little file snake, the absence of a small bony canal connecting the inner ear to the brain case, makes it different from all other known species of snakes. Cover Photo: Gaurav Patil

The little file snake is a denizen of brackish mangrove swamps and is even seen out in the open sea. Photo: Rahulratan Chauhan
Cover Photo: One aspect of the physiology of the little file snake, the absence of a small bony canal connecting the inner ear to the brain case, makes it different from all other known species of snakes. Cover Photo: Gaurav Patil

Both males and females have very rough scales that help them grab and hold on to their slippery quarry. These rough scales give them their name. Additionally, they have tubercles on both the dorsal and ventral sides of their bodies, with which they can grab quickly onto roots, rocks, and prey. These tubercles give them their other name — the elephant trunk snake.

With triangular bodies and loose skin, the little file snake looks like a highly venomous sea snake while swimming. The laterally compressed (flattened from the sides) and slightly paddle-shaped tail (a characteristic that all sea snakes possess) not only help in swimming but in this mimicry as well. Scientists believe that this helps them stay safe from certain predators.

To stay hidden, file snakes have their nostrils high up on their heads, allowing them to breathe while still staying secure and relatively unnoticed beneath the water’s surface. Unlike other snakes, file snakes have lungs that extend the entire length of the body, enabling them to stay submerged for over an hour at a time without having to come up for air! Their low metabolism furthers this cause and ensures they do not have to come up to breathe too often.

The little file snake’s tongue (left) enables it to smell underwater, and its rough scales (right) give it support and allow it to get a good grip on prey in the ever-flowing tidal mangrove creeks. Photos: Gaurav Patil (left), Rahulratan Chauhan (right)

The little file snake’s tongue (left) enables it to smell underwater, and its rough scales (right) give it support and allow it to get a good grip on prey in the ever-flowing tidal mangrove creeks. Photos: Gaurav Patil (left), Rahulratan Chauhan (right)

For most of their lives, file snakes are reported to stay relatively sluggish, remaining in mostly estuarine and open sea salt waters that are between 25 and 30 degrees Celsius. Higher temperatures would cause them to overheat fatally, and lower temperatures would make it impossible for them to function. Like most other vertebrates that live in ecosystems with saline water, the other major challenge that file snakes face is the lack of fresh drinking water. Like sea snakes, the little file snake has salt glands that let them filter out salt from its body. In fact, file snakes have been known to dispense a lot more salt than sea snakes. Another adaptation that is more behavioural than physiological is how sea snakes and file snakes drink water. Since fresh water is lighter than saltwater, rainwater tends to sit as a small layer on top of saltwater, and snakes access and drink this layer after rain showers.

Females reproduce only every alternate year. After mating, the female will carry the young in eggs inside her for between five and seven months. The species is ovoviviparous, meaning the young are born when they have completely developed in eggs inside the mother. We do not know much about the lives of young file snakes or their lifespan. In captivity, they live for up to five or six years. But with males only reaching maturity at four years, this captive lifespan is probably affected by the snakes not getting all they need to reach adulthood. When I’ve spoken with leading herpetoculturists (who breed reptiles and amphibians in captivity), they have almost invariably pointed out that this species needs a lot of care, specific water quality parameters, and their enclosures need a lot of care to ensure natural behaviour. Most believe that the snake does not do well in captivity and requires a lot more research.

This harmless snake is often mistaken for venomous sea snakes and killed. However, the biggest threat comes from habitat loss and unsustainable fishing practices. Photos: Rahulratan Chauhan

This harmless snake is often mistaken for venomous sea snakes and killed. However, the biggest threat comes from habitat loss and unsustainable fishing practices. Photos: Rahulratan Chauhan

File snakes are a unique group of snakes, believed to be only distantly related to all other snakes. One of the primary anatomical differences is the absence of a small bony canal called the metotic fissure, which enables the transfer of sound stimuli to the brain cavity; it’s a characteristic present in all other snakes. This fundamental difference leads scientists to believe that the file snakes evolved parallelly to other present-day snakes. They are not just a variation or adaptation.

Much remains unknown about this species and the group that it belongs to. Despite its uniqueness, the file snake has not been studied much. What we do know is that the habitat type that it has mastered living in is in grave danger, and the rate at which we are losing mangroves might spell doom for this enigmatic species. Neither the little file snake nor its habitat is “sensational”, but both are invaluable parts of a fragile yet indispensable ecosystem. Mangroves are ecologically, economically, and environmentally imperative for our survival and the little file snake, mysterious as it is, is an intrinsic part of our coastal habitat.

Gerry Martin
Gerry Martin

is the founder director of The Gerry Martin Project, and has been involved with herpetological research and conservation, documentary filmmaking, education and eco-tourism over the past decade.


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