What Lies Beneath: Rough-scaled Sand Boa

It’s a late summer morning in a mango orchard on the outskirts of Mysore. A warm, dusty breeze carries the wonderful scent of ripening mangoes. A host of birds feed on insects and forage at every level of the orchard. On the dry, leaf-clad floor, a group of babblers hops around looking for scraps. Suddenly, a tuft of dust and gravel shoots up from below one of the birds. The dust clears to reveal a struggling bird in the firm coils of a mottled snake.

The snake tightens its grip with each of its quarry’s frenzied breaths until it is completely still. Then, once it senses no heartbeat, no breath, and no life in its prey, this brown, rough-skinned snake relaxes its grip, sniffs around for the bird’s beak and starts swallowing its meal headfirst in the now silent orchard.

The rough-scaled sand boa (Eryx conicus), also known as the common sand boa in India, is very common in arid and semi-arid regions across the lowlands of South Asia. It is regularly encountered in towns and cities with large open or garden spaces. In rural agricultural landscapes, it is frequently seen at the edge of fields, in holes, on embankments, and amid piles of rubble, vegetation, and compost. During the rainy season, it is often spotted inside homes, crossing roads at night, and even taking refuge in tree hollows when the ground is particularly waterlogged.

Around my home, near Nagarahole Tiger Reserve, close to Mysore, I regularly find these snakes under the granite stone slabs that form the pathways around the farm. One individual stayed under the front step of our home for almost four months and became very accustomed to us walking over it. One day, it was gone, probably to find another spot where it could wait in ambush for prey or possibly find a mate.

In October 2022, we found four sand boas in one hole in an embankment in our neighbour’s field. He’d called us, saying there was a Russell’s viper in his field, which he wanted us to move. When we got there, we saw one sand boa outside the burrow and another coiled inside. There were four snakes altogether, one female and three males. It was the beginning of the breeding season. The snakes were left together to continue with their business. The breeding season in our region goes on till late December. After this, the males head off, and the female needs to feed well to produce viable eggs that she will carry inside her till they are ready to “hatch”. 

These fossorial (burrowing) snakes are well-built for life underground. Their “rough” scales are intensely keeled. A keel on a reptile’s scales is a ridge that runs down the middle of each scale, and under close inspection, looks like an inverted keel of a boat. Rough-scaled sand boas possess keels that are so intense that their skin helps hold soil granules and leaf litter on them. This provides added cover when the snake is waiting just beneath the surface of the soil for an unsuspecting bird or rodent to get close enough for the snake to grab in its jaws and coil around it.

This effective hunting strategy is something that works very well on rodents and birds that forage on the ground. However, they are too large for a newborn or juvenile sand boa. Babies take small skinks, frogs, and young garden lizards. One would wonder how this slow-moving snake is able to ambush enough prey to feed itself. The answer comes from a single report from 2011 of a juvenile rough-scaled sand boa in captivity in the United States that responded to a fuzzy mouse hopping on it by raising its tail and “caudal luring”. 

Caudal luring refers to the snake slowly wriggling its tail like a worm to attract insect-eaters like frogs and lizards closer until they’re within striking range. It’s not entirely surprising that this snake would do this. When it’s a baby, its tail is much lighter in colour than the rest of the body. Good musculature in the tail enables it to wriggle it and ambush prey. Many snakes that ambush their prey have ways of attracting the prey closer. This behaviour has not been previously recorded in India. It’s one of many examples showing us we have to spend time observing animals and reminds us how little we know about snake behaviour and ecology.

In South India, sand boas give birth between April and June, and we start finding these pencil-thin babies in our compost piles and vegetable patches. They’re in time for the pre-monsoon showers that generally trigger a lot of life, from insect emergences to the prolific breeding of frogs in ephemeral pools and the hatching of numerous species of lizards (including skinks and garden lizards). These creatures are likely to be lured into coming closer to check out a wriggly worm and meet their fate!

Still, this is an assumption until we dedicate the time and resources to better understanding snakes considered “less sensational”. The sand boa is a non-venomous, harmless snake that doesn’t fit the stereotypes of brilliantly coloured, dangerous, huge, or feisty. But, these boxes that we tend to put snakes into are more indicative of our lack of insight into their biology and behaviour than their lack of evolutionary brilliance. It is time to look deeper into these wonders of the “underworld”!