I love all living beings — the smaller the better. It is little creatures like bacteria, termites, ants, millipedes, earthworms, snails, rodents, frogs, fungi, lichens, herbs, and shrubs that keep our terrestrial ecosystem running. The general public may prefer larger, more glamorous animals, but once we begin to appreciate or understand how habitats function, all creatures become equally interesting. Here, I am going to talk about a group of insects known as “dung beetles”, found everywhere except for the polar regions. There are over 30,000 species of dung beetles, and this diversity itself proves that these creatures are required in every terrestrial ecosystem.
Taxonomically, dung beetles belong to a superfamily of beetles called Scarabaeoidea. Based on their lifestyle, they are further divided into two families: Geotrupidae (the earth-boring dung beetle) and Scarabaeinae or true dung beetles, as most members feed on dung.
Functionally, dung beetles are divided into three broad categories: rollers that make a ball of dung and roll it away to bury elsewhere; tunnellers that bury the dung wherever they find it; and dwellers that neither roll nor burrow, but simply live in dung.
Out of the 30,000-odd species of scarabs in the world, nearly 10 per cent or 3,000 species are found in India. Although they are found all over India in various forms, they are best seen in dry and semi-dry habitats. (Forest dung beetles are difficult to find although there are more species.) Large, black dung beetles are a staple scene in wildlife documentaries, often filmed rolling a large dung ball with energetic dexterity despite obstructions. The determination to take its ball away from its rivals must be seen to be believed.
Dung beetles have a heightened sense of smell, and they are attracted to the “aroma” from half a kilometre away. Photo: Dhritiman Mukherjee Beetles are the largest group in the animal kingdom, distinguished from other winged insects by their hard, outer wings. There are over 3,50,000 species of beetles on Earth, of which dung beetles are one category. Cover Photo: Dhritiman Mukherjee
But, why do they make a ball of a dung? For two simple reasons: to eat and to propagate. Some species make a ball and bury it for later consumption, while many species bury the ball for the female to lay an egg in it later. When the larvae hatches, it eats from inside, pupates, and emerges as an adult to continue its life cycle.
Why dung, and not other food? Because most dung is nutrient rich, particularly of large ungulates that defecate partially digested faeces or dung, Some species simply ride on their dung-supplier and drop down when fresh dung falls, to devour it or roll it away. A wonderful example of how nature does not allow any waste. Many dung beetles also feed on fungi, rotting leaves, and bark, so dung is not the only food of every species of this taxon. Some have become predators, preferring live food (millipedes) to rotten carcases or dung.
The Desert National Park, near Jaisalmer in Rajasthan, is a good place to sight dung beetles in action. Photo: Dhritiman Mukherjee
The power of a large dung beetle is described in folklore and fables all over the world, dating back to ancient Egyptian times. Let us make a modern-day comparison, by measuring it against the World Wrestling Entertainment (WWE), that is famous — some say notorious — for large-bodied contestants, trying to beat equally powerful rivals. Milligram for milligram, these muscle-rippling wrestlers are no match to a dung beetle called Onthophagus taurus. This 5.5–11 millimetre, oval-shaped beetle has achieved the distinction of being the strongest insect in the world.
In a paper published in the Proceedings of the Royal Society B (2010), Dr Rob Knell from Queen Mary University of London, and Professor Leigh Simmons from the University of Western Australia, found this strong beetle could pull 1,141 times its own body weight — the equivalent of a 70-kg person lifting 80 tonnes (roughly the same as six, double-decker buses full of people). Like our bodybuilders, scientists found that beetles follow a special diet to gain strength, but when deprived of proper nutrition, they become weak and reluctant to fight.
But why so much pain to build their body? Sex is the answer. Female dung beetles are very choosy, selecting the most powerful mate for sex. When she is ready, the female waits in her hole, allowing her strong pheromones to waft out and attract contending males. The suitors that arrive must then fight, until there is only one male left in the narrow passage. All others are kicked out.
Many species of birds, including the great grey shrike, eat dung beetles, as they are a plentiful source of nutrition. Photo: Dhritiman Mukherjee
There is a huge body of literature on the dung beetles, describing their important role in the functioning of the ecosystems, and how they are ecosystem engineers in many cases. With the distribution of dung in the form of balls, dung holes, and tunnels, they keep our farmland fertile. Many dung beetles control insect pests, and recent studies prove that their tunnels may even help in reducing greenhouse gas emissions. As the famous biologist and writer Prof EO Wilson said, beetles “are the little things that run the world”.
Dung beetles are a food source for the critically endangered great Indian bustard, and the large birds love eating them. When I was conducting studies of the bustard, I found them searching for beetles, and also spotted the undigested, hard wing covers (elytra) of the beetles in their faeces. Some locals told me that they do not eat bustard as it feeds on beetles, scorpions, and snakes. Whenever forest officers and misguided activists say that grazing should be stopped in the bustard closures (core area) of the Desert National Park in Rajasthan, to help the bustard survive, villagers give the example of bustard “following” grazing livestock herds to eat the dung beetles that appear as soon as fresh dung falls on the ground.
The villagers may not be entirely correct but they are not wrong either, as cattle dung attracts lots of dung beetles. Incidentally, livestock grazing is not a problem for the bustard or any other grassland species as grass and grazers have co-evolved — it is severe overgrazing that is the problem. Controlling overgrazing (by limiting cattle numbers in core areas) is the administrative step we need, and where managers of most protected areas fail. So, the best step is to ban all livestock grazing with ecological consequences that most people cannot comprehend.
I could locate many research papers on the taxonomy or checklists of dung beetles, but good papers on the ecological role of dung beetles are lacking in India. I think these fascinating little creatures need more attention from conservationists, ecologists, and entomologists. Once we start studying them, I am sure we will find that their muscle power and fights are more enthralling than the dudes that we see on WWE.
