Dung beetles

ambika kamath | Updated on September 12, 2014

Sisyphean task? Dung beetles roll the ball using the sun for orientation   -  Divyaraj Shah

The scatological insects who know both the Milky Way and dino droppings intimately

Put away your cup of coffee or piece of toast for a minute, and let’s talk about dung beetles. Why dung beetles, you ask? Because no animal better exemplifies the notion that one creature’s waste is another’s entire existence. For a dung beetle, dung is more than just its roti aur makaan — battles are fought and hearts are won over a pile of dung.

Dung beetles come in several varieties, each with a different relationship to dung. The ‘tunnellers’ tunnel through dung to build nests in the ground below, carrying dung into these nests to both feed on and lay eggs in. The ‘dwellers’ set up shop right in the dung pile, expending no effort beyond that required to burrow just beneath the surface. But the first beetles to arrive on the scene following the production of a fresh pile of dung are the ‘rollers’. These beetles quickly roll a ball of dung away from the pile before burying it, attempting to minimise competition with both other rollers and the onslaught of tunnellers and dwellers who arrive soon after. But arriving first isn’t always enough to avoid competition — individual rollers who find themselves without a dung ball of their own will launch into vicious combat with rollers who are rushing away from the pile with their hard-won dung balls, trying to wrest control of the precious resource. For the early-arriving rollers, therefore, speed is of essence. But getting far away from the dung pat as fast as possible necessitates knowing exactly where one is going. To be able to move in a straight line directly away from the dung pile, some beetles have evolved to orient themselves based on the sun. But what about the species that are active at night? They use the light from the moon instead. But what do they do on nights when the moon isn’t visible? It turns out, dung beetles can use starlight — the orientation of the Milky Way, in particular — to keep track of where they are going!

It isn’t just the rollers that have evolved impressive features in response to competition. Male tunnellers also battle fiercely with one another, defending access to females who will lay their eggs within the tunnel nests. Rival males fight over who gets to father those eggs — they lock horns with each other at tunnel entrances, and males with bigger horns prevail. Species of tunnelling dung beetles therefore possess a diverse array of impressive horns, including some species whose horns are outrageously large — they can weigh more than 15 per cent of the total mass of the beetle. Calculate how much 17 per cent of your body weight is, and then imagine hauling that weight around on your head, for the sake of dung.

One testament to the value of dung as a life-supporting resource is that dung beetles are found on almost every continent. But perhaps more compelling is the fact that these beetles have been going about their lives of rolling, burying and burrowing into dung for millions of years. There exist fossils of dinosaur droppings that bear distinct evidence of being used by tunnelling dung-eaters, most likely beetles.

Would you have imagined contemplating the dung beetle would launch you into the far reaches of space and time? I certainly didn’t.

Ambika Kamath studies organismic evolutionary biology at Harvard University

Published on May 16, 2014

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