'Home is where the dung is'

Published in Welsh Country Magazine, January 2010

How much dung would you expect one average-sized cow to produce in a year? Not sure? Well, one cow will produce at least 9 tonnes of dung per year. With over 10 million cattle in the UK, that's over 90 million tonnes of dung produced yearly...and it's not only cattle that produce dung! It has been calculated that one dung pat will cover 0.8m², so add all this dung together and cow dung would cover an area of 292,000 hectares. We can put this into perspective when we realise that London covers only 159,000 hectares. So where is it all? Why are we not neck deep in the stuff?

It is because there is a whole hoard of organisms that call a dung pat home. Many people are under the impression that dung beetles are only found in Africa. However, we have over 100 different species of beetle that inhabit British dung. Of these, around 50 species are classed as ‘dung beetles' as they actually feed on the dung itself. The majority of British dung beetles are in the genus Aphodius. These brown, black, red, yellow and russet beetles are between 0.3mm-20mm long, and live and feed within the dung pat, laying their eggs either within or under the pat. Their larvae develop in the dung using the nutrient-rich food source to grow. They will then pupate and most emerge as adults the following year.

Other larger dung beetles, notably Onthophagus spp., the Dor beetles and Minotaur beetles bury dung under or next to the dung pat. After burying the dung, these beetles lay their eggs in it, providing hatching larvae with a warm, moist nutrient-rich environment in which to begin their life. The other 50 or so beetle species that you are likely to find in dung include rove beetles, water beetles and hister beetles. Rove beetles (otherwise known as Staphylinidae or Devil's coach horse beetles) are long narrow beetles with short wing-cases with the body segments clearly visible. These beetles, along with the black, shiny hister beetles (Histeridae) are important, voracious predators feeding on pest-fly larvae and other undesirable dung parasites. Water beetles (Hydrophilidae) evolved to live in water, but have now modified their legs to allow them to literally swim through dung.

The Ancient Egyptians were so bemused by dung beetles hatching ‘spontaneously' from what they thought was an innate ball of dung, that they worshiped the dung beetle (otherwise known as the Sacred Scarab Beetle) as a symbol of spontaneous creation and rebirth. Kheperi, the dung beetle god was believed to push the setting sun along the sky in the same way that a dung beetle rolls a ball of dung along the ground. Each day the sun would disappear and be ‘re-born' the following day.

Dung beetles play a key role in the process of decomposition. Not only do dung beetles bury the dung themselves, but by moving through the dung, they aerate it, allowing earthworms to enter and begin breaking it down further. Without dung beetles to do this, earthworms would not be able to enter dung and break it down. Dung beetles also carry with them fungi and bacteria from pat to pat, which again speed up the decomposition process.

In agricultural systems, the cycling of organic matter through herbivore dung into the soil plays an important role in helping to maintain pasture fertility and productivity. The healthier the dung decomposer community, the higher the rate at which dung is broken down and removed from pastures. When a healthy dung beetle community is not present, dung forms a hard crust and remains on the surface. It then acts as a breeding ground for pest flies and worm parasites, causing pasture fouling and an increase in pasture worm burden. It has been shown that without dung beetles to break dung down, the un-degraded dung from 10 cows will remove 1 acre from production per year! Dung beetles are also an important food source for declining farmland birds and bats: dung beetles constitute a large percentage of the diet of both the chough and greater horseshoe bat. The feeding activity of birds in dung also helps to further break up the pat.

By burying the dung, dung beetles are actively putting nitrogen back into the soil. If we can encourage our dung beetles to do their job efficiently, we may even be able to save on nitrogen fertiliser application and make better use of manure and slurry. We are then also reducing carbon footprints and chemical inputs.

It has been estimated that dung beetle activity saves the loss of $380 million to the US cattle industry per year. The importance of an appropriate dung-decomposer insect community was perhaps most clearly demonstrated in Australia where the native dung beetles, which feed preferentially on dry marsupial dung, were unable to feed on the wetter dung of introduced large herbivores such as cattle and horses. The result of this was extensive pasture pollution and increased pest fly populations, necessitating a major programme to introduce exotic dung-burying beetles.

How can we help our dung beetles?

British dung beetles are in trouble. With many species already extinct and other well on the way, we need to look closely at what we may be doing to cause these declines. As many species of dung beetle are active during the winter, the removal of livestock from grassland during the winter months effectively removes the dung beetles' food source i.e. the dung. The reduction in the number of out-wintered cattle in the UK has lead to serious declines of our dung beetles.

Dung beetles are also adversely affected by chemical livestock wormers (anthelmintics): over 95% of the initial dose ends up in the dung and continues its insecticidal effect, killing our dung beetles. It is important to always have some dung available for the dung beetles from animals that have not been recently treated with chemical wormers, and to reduce the frequency of chemical worming as much as is possible whilst still taking account of animal welfare. The wormer Cydectin has been marketed as ‘dung beetle friendly' and does appear to have less of a detrimental effect on dung beetles than many other wormers. There are also alternative supplements on the market which claim to reduce parasite burdens in livestock, such as diatomaceous earth (DE), homeopathic products and the herbal-based Verm-X. However, the impact of these as well as other veterinary medicines and supplements on dung beetles is as yet unknown.

So next time you walk past a cow pat, give it a poke with a stick and you may be lucky enough to see one of our great decomposers in action.