The unexpected little underdogs of the big bad desert

Deserts are harsh ecosystems defined by high daytime temperatures that can dehydrate bodies quickly and low night temperatures that demand warm shelters. Despite the extremes, deserts are sanctuaries to a diversity of life forms. Animals living in these habitats have adopted mechanisms to cope with the fluctuating temperature, low water availability and, at times, scant food sources.

The adaptability of mammals, such as camels, foxes and gazelles, reptiles and even birds in deserts are well-documented. However, there are other creatures that are vital for these ecosystems but are little known or rarely discussed – insects, for instance. Insects have an important role in all ecosystems and deserts are no different. In fact, a biodiversity count of desert species would probably show insects topping the list. With climate change forecasting a warmer earth and desertification now a reality, it would be worthwhile to learn how these creatures survive in unforgiving habitats.

Eighty-five percent of the Thar desert (roughly 170,000 square kilometres) is in Rajasthan, India. Several parts of it are protected as sanctuaries or national parks, the largest ecosystem being the 3,162 square kilometre-stretch in Jaisalmer – the Desert National Park. The eastern part of the desert receives more rain and is, therefore, more humid than the north and north-western parts that are quite arid. These conditions – temperatures, atmospheric precipitation and relative humidity – determine the nature of living organisms found here. The Park is most famous for the Great Indian Bustard, but cohabiting with the bustards, vultures, gazelles, reptiles and humans are diverse insect species – beetles, bugs, butterflies, crickets, grasshoppers, moths, and mantids, among several others. Some of these, varied in diversity and adaptations, are unique to this region.

The little-known dune cricket

One such unique inhabitant of the Thar desert is a cricket species hardly known outside entomology circles. There is only limited knowledge of the ethology and biology of these difficult-to-study nocturnal insects that still have entomologists groping in the dark.

The dune cricket belongs to the family Schizodactylidae. Entomologists who first came across this insect in the early 19^th century categorised it as just another species of the cricket family.  It was years later that detailed studies were undertaken that established that although it belonged to the order Orthoptera (which includes the grasshoppers and crickets), it was not of the ‘true’ cricket family, as thought earlier.

The world over there are only two genera of this insect – the winged Schizodactylus from Eurasia and the wingless Comicus from Africa. Schizodactylus is represented by six species, all found in northeast India. They are a delicacy for the Gola tribes of Arunachal Pradesh. Only two of the six species, namely Schizodactylus monstrosus and Schizodactylus minor, inhabit the deserts of Rajasthan. Villagers of Jogar in Jaipur, where these insects are a common sight in farms, call them Moochhar, meaning ‘one with a moustache’, a reference to the antennae of this insect that measure nearly six centimetres or more. Recently, a seventh specie, Schizodactylus salweenensis, was discovered in Thailand.

Schizodactylus monstrosus, although known to very few, is among the most common in India. When noticed, the most frequent reaction the insect invites on itself is a stomp of the shoe. Not unlikely because manhandled, it bites ferociously. And it looks the part.

Compared to a ‘true’ cricket, which usually ranges from 10-25 or 30 mm, a dune cricket is quite large in size, always larger than 30 mm. The big mandibles and long, robust legs with expanded tarsi (feet) give it a somewhat menacing appearance. The posterior end of the wings is spirally coiled, limiting its ability to fly. So, the dune cricket runs.  The paddle-like projections of the tarsi, that explains the moniker ‘splay-footed cricket’, is not only an adaption to aid its burrowing nature but also serves to support its large body as it hunts for prey in the sand.

These insects have an important role in the desert ecosystems. The adults as well as the nymphs are exclusively carnivorous, preying on beetles, grasshoppers, and other small insects for food. Survival of the fittest is the operant principle in the life of these ferociously cannibalistic creatures, which are even seen to pounce on each other when they come out of their burrows in search of food. In the desert food chain, these crickets are fodder for reptiles like snakes and lizards and birds such as partridges (chukar), falcons and whistling ducks.

First discovered in the sand beds of Damodar river that flows through West Bengal, the Schizodactylus monstrosus was initially nicknamed ‘cricket of Bengal’. Subsequently, it came to be called the maize cricket, splay-footed cricket and also earned the sobriquet ‘Bherwa of Bihar’, each name indicative of their behaviour, morphology and/or ecology. Bherwa is the local name for a type of date palm, which, like this cricket, needs sandy soil to survive.

The question of water

Dune crickets, as the name suggests, prefer sand dunes to live in and, because they cannot survive dehydration, they prefer dunes close to water sources. In fact, tunnels they build in the dunes have been observed to be wet inside. So, they can actually be indicators of the presence of water in otherwise arid regions.

In the Thar, these crickets mostly inhabit the Sam dunes, the vast stretch of shifting sand dunes near Jaisalmer. Some believe that the construction of the Indira Gandhi Canal, which starts from the Harike Barrage near the confluence of the Sutlej and Beas rivers in Punjab and brings water to the Thar, may have encouraged the species to migrate here – a suggestion contested by many.

But why choose a punishing desert for home?  No one knows yet. How do these crickets survive the harsh desert conditions? Insects usually have certain evolutionary advantages to survive dry and hot climates. Their exoskeleton, made of a hard shell-like substance called chitin, helps to avoid loss of water from the body to a certain extent. However, the large soft body of the dune cricket is not sufficiently chitinous to prevent dehydration. There has to be another way by which the dune cricket protects itself in the extreme Thar climate.

Nocturnal and fossorial

The answer probably lies in the habitat and lifestyle of dune crickets.

Stay safe underground till the sun goes down is a mantra for most desert dwellers, especially small creatures like dune crickets. Propagators of a nocturnal and fossorial (or burrowing) lifestyle, dune crickets dig isolated tunnels – each one for itself – in the sand, where they stay all day. This does more than just offering protection. Studies have shown that in deserts, water supply from fog and dew is comparable to, or can even exceed, the amount of water from rainfall in the area. Tunnels made by dune crickets are designed to let water droplets flow inside.

Not just adults, even nymphs (young insects) make isolated tunnels in the sand, with very few opting to dig near embankments if they are near a water source. Different tunnels for different purposes – to live, to mate or to lay eggs. The design and structure of the tunnels ensure that they last. They are long, slanting and could be about 100 centimetres deep sometimes. The length of the tunnel, on an average, is between 40 to 60 centimetres, with a diameter of 5 to 5.5 centimetres. The depth could range from 20 to 60 centimetres, with a few going down even up to 100 cm. The depth is determined by the water table and digging stops when presence of water is noticed. The riverine species of dune crickets build their tunnels at least a metre away from the water source. In deserts, researchers found that the depth at which the S. monstrosus were found varied in the months of summer and winter and was determined largely by temperature and relative humidity of the sand.

Digging a 100cm-deep tunnel in shifting sand is strenuous work. For long it was thought that the ‘splayed feet’ were tools for dune crickets to burrow. It was entomologist F. Carpentier in 1953 and later Narain Khattar in 1972 who confirmed that digging in the sand was done using the large mandibles. While the strong and hardy mandibles dig swiftly, the excavated sand is quickly pushed out with the hind feet. The expansions on the hind tibiae block the sand from falling back into the tunnel. The excavated sand accumulates into a little mound that is used to create a plug to close the mouth of the tunnel. Tunnels are closed after the insect goes in, and there it stays. Once out, it never goes back in. A fresh tunnel is built all over again. The nature of the sand plug thus is the clue to detect the presence of the insect. A fresh sand plug indicates that the cricket is inside. The height of the sand plug and the diameter of the tunnel indicate whether the insect is an adult or nymph. The bottom of the tunnel is generally wider and the insects reside facing the opening of the tunnel. While young adult crickets go deep in search of water and build closed tunnels that are quite deep, open burrows are generally built on river embankments and occupied by aging and less active crickets for whom they serve as traps to capture prey.

Apart from functioning as digging tools, the distinctly large mandibles of these crickets also serve to keep them safe. Entomologists Prathapan Divakaran who teaches at Kerala Agricultural University in Thiruvananthapuram and H.M. Yeshwanth from Gandhi Krishi Vignan Kendra, Bengaluru, who went looking for them in Rajasthan, found proof the hard way. Only after several painful bites did they manage to capture two adult crickets for their study, the entomologists told the writer.

The incident is a testimony to the fact that the diminutive-looking dune crickets are a force to reckon with in the desert ecosystem – armed to protect and sustain themselves in climes even humans struggle to survive.

CITATION:

Hazra, A. K., & Tandon, S. K. (1991). ECOLOGY AND BEHAVIOUR OF A SAND BURROWINGINSECT, Schizodactylusmonstrosus (Orthoptera: Schizodactylidae). Advances in Management and Conservation of Soil Fauna, 805-809.

Hazra, A. K., Barman, R. S., Mondal, S. K., & Choudhuri, D. K. (1983). Population ecology of Schizodactylusmonstrosus (Drury) [Orthoptera] along the sand bed of Damodar river, West Bengal, India. Proc. Indian Acad. Sci. (Anim. ScL), Vol. 92. Number 6, 453-466.

Prakash, I. (2001). Nature Watch – Biological Invasion and Loss of Endemic Biodiversity in the Thar Desert. Resonance, 76-85.