More on dung beetles

Hello – Many thanks to Faye and Paula for your kind comments. This post is in response to the question about dung beetle’s and why they have such fantastic ornaments on their heads. Firstly, much of the head structure serves a very practical purpose – the toothed, curved edges serve as an effective shovel with which to push under, burrow through and even help loosen dung for scooping up with those remarkable front legs.

 

In some species, the males have some elaborate horns and other structures on the heads. These are used to impress would-be females, as well as to fend off the competition: i.e. other males intent on stealing a hard-won ball of dung after a hard day’s work of packing it together and rolling it along. The horns also help the male of species where he is made to stand guard by the female in the tunnel that leads to the chamber where they raise their offspring. What’s even more amazing is in some cases the male dung beetles have to make rather awkward trade-offs. Basically, the larger and more elaborate their horns, the smaller and more useless their eyes! Imagine having to ‘choose’ between being able to see or looking sexy for your mate!

 

To most people, the toiling dung beetle, diligently rolling its ball of dung across the path, struggling over rocks and through clumps of grass, represents a hard-working insect, to be admired for its ‘Protestant’ work ethic.

 

Human cultures through history have noticed the dung beetle. The most devoted of the dung beetles fans were without question the ancient Egyptians. The scarab (dung beetle), seen rolling its ball across the ground, burying it, and coming back to life, was interpreted as a symbolic of the ‘death’ and ‘resurrection’ of the sun each day. Therefore, just as the scarab returned each day with the ball of dung, the scarab-god Khepri, rolled the sun across the heavens during the day, buried it in the evening and dragged it out again at dawn the next day. Since the scarab and the sun both emerged from the ground after being buried, this belief is also thought to have influenced the construction of the pyramids, from whose entombing depths, the deceased could also resurrect. The dung beetle continues to be honoured today by the scarab epithet in that their beetle family is known as the Scarabaeidae and an entire genus bears the name Kheper.

 

The rolling of dung, however symbolic, is just the beginning of many a dung beetle’s labours. Dung beetles, converging on a fresh pat of dung, have different approaches and life-cycles. Dung rollers, those who actually make balls and roll them away, are one group. Others excavate tunnels beneath or next to the fresh dung and roll dung into them. Yet others, tiny and often overlooked, simply feed and breed in the pile of dung.

 

Within each group of dung beetles, the roller-aways, tunnel-beneaths or stay-putters, different and complex behaviours have evolved. Those species who tunnel under the dung often work in pairs. The males, armed with horns, as in the genus Copris, stand guard in the tunnel. They do this to block other males and potential dung-thieves from harassing the female who is busy beneath, preparing the dung for egg-laying. Species that simply breed in the dung are tiny, known as dung chafers, and develop rapidly. Some of them also use dung stashed by other beetles to breed in.

 

More honest and hardworking, are the rollers. The efforts devoted to roll the dung away from the source are primarily aimed at limiting competition. It is usually the males who converge and make the balls. Using their specially-adapted forelegs, armed with special ‘teeth’, they deftly and quickly sculpt the fresh dung into a sphere. Amazingly, the same fore-legs serve both as industrious spades and fine sculpting tools.

 

Access to fresh dung is crucial for dung rollers. And the competition can be stiff. Watching a group of dung beetles on fresh buffalo dung in Nairobi National Park, some time ago, I learnt just how determined dung beetles can be:

 

A herd of buffalo have just passed through. Marking their passage, in large, fresh steaming pats, are piles of dung. Within minutes, the dung beetles arrive. There are at least five different species, some tiny, commonly known as dung chafers, one small but bright green and typical blackish rollers – Scarabaeus.

 

The rollers settle down to work and soon there are several nice round balls ready. The males are the ones who sculpt the balls in this species- the first ball made is the nuptial ball. A female approaches him and he immediately tries to copulate. He is rejected at once and put to work. The male now grasps the ball with his elongate hindlegs, and head pointed down, begins to push. The female, perched on top of the ball, rides piggy-back. Struggling over exposed roots and around stones, the male furiously rolls the ball of dung away from the pile. It is essential to get away from the madding crowd, and would-be competitors, as quickly as possible.

 

Just as he gets the dung-ball and the female to the edge of a clump of grass, another male spots them. The interloper speeds towards the rolling pair. Her grabs the ball and tries to climb on. The first male, sensing the presence of a challenger, stops rolling and climbs on to the ball. The interloper grasps the ball hard and pushes himself under the ball’s creator. The fight begins. Using their hard, toothed heads, the two tussle and attempt to push each other off the ball. Meanwhile the female remains calmly seated on the side of the ball, she even takes a small nibble while the males tussle.

 

Back and forth the ball rocks as the two males ‘lock horns’. After half a minute of wrestling, the interloper has been forced onto the side of the ball. Distracted perhaps by the female, he raises his head slightly. The other male seizes the moment and thrusts his armoured head underneath his opponent. With a quick powerful flick, he tosses the interloper from the ball. The interloper lands on his back and waves his legs trying to right himself.

 

The victor gloats, standing atop his ball and surveying the area, as if to say “ would anyone else like to take me on!” The ball meanwhile, has been damaged in the tussle and the male quickly repairs it, gently combing the dung back into place. The female stays put through all of this. They resume their journey. He pushes and pushes, and finally the ball comes up against a twig (mischievously placed by yours truly) across their path. How will they overcome this obstacle, the dung beetle equivalent of a fallen tree blocking a road, I wonder?

 

The edge of the ball comes to rest against the twig. The male, unaware of the obstacle, continues pushing. He tries for a couple of minutes then realising that they are going nowhere pauses. He shuffles sideways and tries again, he manages to move the ball about an inch, but then it wedges fast. I watch with some guilt, as he pushes again, from another angle, to no avail.

 

Just as I reach down to move the twig, the female dismounts. She positions herself next to the male and with an antennal twitch to egg him on, begins pushing. Their combined efforts easily roll the ball over the twig. They pause, the male takes a moment to scan the area. The female climbs back on and they carry on with their journey. A snort in the near-distance reminds me that I should not become too absorbed in the dung beetles. I look up. It’s just a warthog. Phew! I look back down, the beetles and their dung ball have rolled off into the grass.

 

The dung beetles will take their ball into a specially excavated burrow. Here the business of egg-laying and brood rearing will take place. Depending on the species, the male is expelled, made to stand guard in the tunnel, or allowed to watch- sometimes he helps. The female meanwhile prepares the balls. This involves coating the balls with so
il and layers of semi-liquid faeces. This is essential to keep the fermentation in the dung going.

 

After a number of days, when the dung is well-ripened, she breaks off pieces and sculpts ‘brood balls’ from these. Within each an egg is laid and then covered up. For the next weeks or even months, she remains on her brood balls. Endlessly licking and cleaning them, removing larval wastes. Without this attention the larvae would soon succumb to attack by mould and bacteria. In some species the eggs and larvae are left to their own devices, but in this case they are carefully tended and have high survival rate. They are also fewer in number- 1-2 or 2-4, given the greater investment in survival. Species who don’t tend their young lay many more eggs to increase their chances of survival.

 

The actions of dung beetles burying dung do more than just provide food and secure new generations of dung beetles. In habitats typified by large herbivores, were the dung not removed from the surface, it would accumulate to unhealthy levels. Dung that is buried breaks down faster than that on the surface, as any composting gardener can tell you.

 

An example of the subtle ways that dung beetles shaped habitats comes from western Uganda’s Bwindi Impenetrable forest. Forest-dwelling primates, including chimps, are primarily fruit-eaters (frugivores). Their dung, correspondingly, is often laden with the seeds of fruiting trees. As they travel through the forest, they disperse the seeds far and wide. However, most seeds land on the forest floor and are soon gobbled up by rodents.

 

This is where the dung beetle comes in. Certain dung beetles in Bwindi, and throughout tropical African forests, specialise in frugivore dung. They quickly locate and bury fresh, seed-filled dung. As a result, the primate-dispersed and softened seeds are safely planted, away from scrounging rodents, at just the right depth. For some large-seeded tree species, including Monodora myristica, the survival/germination rate is many-fold higher when buried by dung beetles. Monodora, a member of the Annonaceae, is pollinated by beetles. Therefore, this tree relies on beetles for both producing and planting it fruit!

 

Dung beetles, like so many other insects, play an essential and integral role in the continued health of ecosytems, as well as human ranching and pastoralism, across the world. They provide an efficient (and free!) waste-disposal service. The species that engage in elaborate brooding behaviour and care for their young represent a highly evolved system. They help keep habitats healthy and indirectly, us too! Think of the many roles filled by their singular task when you next spot one rolling its ball down the road!

Below are a couple of sketches showing the life-cycle of a typical dung beetle in East Africa. And a chimp feasting on a juicy fig – little does he know that his meal is thanks in part to the humble dung beetle!