Valle de Puértolas - Puyarruego
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Dung beetles

People come to the region to visit the Ordesa National Park, to climb the Monte Perdido, to do some canyoning or bird watching (see our bird list), to hunt for plants and butterflies; in other words they come to enjoy a stay in a habitat they consider natural. An important part of the mountain landscape however would perish without the intervention of humans and their cattle.

The mountain pastures can only survive thanks to the many sheep and cows grazing the alps during the summer months. But dung beetles are at least of equal importance in maintaining the pasture ecosystem. Research has shown that cows don't graze closely to their own manure pats (even though the grass isn't contaminated). Without beetles the dung of cows or the sheep's droppings would stay at the surface for months making a considerable surface of grass unpalpable for the grazers.

Let's try to forget about the somewhat disgusting food preferences of dung beetles and focus on their good work. Dung beetles are drawn to manure by odour. They can detect a fresh dropping from a large distance and sometimes (particularly on hot days) attack a new patch seconds after it hits the ground. Many are good flyers and you can often find them during the night circling the street lights.


In the present context three types of behaviour are important.

  • Rollers are probably best known. Dung beetles in laymen's books are always busy rolling a pill of dung. The pill is then burried in a deep cavity and seeded with an egg. Sisyphus species are rollers.
  • Tunnelbuilders do build nests below the patch. The nest is a sometimes complex system of galeries ending in chambers with one egg each. Onthophagus and Caccobius species are tunnelers.
  • Dwellers don't engage in deep digging. They just wander around in the abundance. The larvae live within the dung pile. Aphodius species are dwellers.

Dung beetles, while procreating, are working plenty of good things for the ecosystem. Their tunneling brings organic matter from the dung pat down into the soil where it becomes available for bacteria, fungi and earth-worms energetically brewing humus. The digging improves the airiness and increases the water holding capacity of the soil. As dung beetles feed and crawl they compete with maggots and make the environment unfavourable for the further development of flies. Research has shown that parasites of cattle are having difficulties completing their lifecycle. The circle gets broken together with the dung pile.

The beetles we're talking about until now are dung beetles s.s. Manure is their food and their home. But many other species belonging to other families are also regular visitors of manure. In fact should we pick a sheep dropping or a cow pat and follow it in time we would witness a rapid succession of several kinds of interesting critters. Most don't feed directly on manure but on the produce of this small ecosystem in rapid evolution. Some feed on bacteria or fungi. Other species are carnivorous and attack the eggs or young maggots of flies and larvae of other beetles.

The first arrivals, often within seconds, are beetles who like to swim in the fresh and juicy manure. They range from 1 to 5 mm and belong to the genera Cercyon and Sphaeridium of the family Hydrophiliidae, a family with many other species found in water. Their presence (at least of the bigger species) can easily be diagnosed. The patch features several holes measuring about half a centimeter diameter. Don't come too close and don't make fast movements because the beetles are very shy. Stay quiet, make sure that your shadow is not on the object of your study and wait. After a while you will see beetles emerge from the holes and before you know you will witness a dense and rapid traffic between the holes.
Most beetles of this group wont stay long before moving on.

Side step

Butterflies are also regular visitors of a nice dropping. Like the adult dung beetles they are after the liquid contents of the excrement. Our pictures show butterflies belonging to five families while they take a mineral boost.

But let's go back to our main thread.
The next visitors are the real dung beetles like Onthophagus and Aphodius of the families Scarabaeidae and Aphodiidae.

Many of the other species drop in after a solid crust covers the manure. They belong to the families Staphylinidae (although some species - e.g. Oxytelus - arrive quite early) and Histeridae. The adults and larvae feed on the rich animal communities which have had time to develop during the previous days. Sometimes even Carabid beetles come by to have lunch.

Which species of the named families are present depends on several conditions :

  • The kind of manure (many beetles have their favoured manure: sheep, cow, horse, dog, etc.)
  • The altitude above sea level
  • The season of the year
  • The local climate
Changes in cattle breeding can cause a decline in species richness. In earlier times, during summer the herds were grazing on the mountain pastures. Autumn came and shepherds brought the ruminants down to the winter grazing land, often quite far away to the south. During this so-called transhumancia the herd followed dedicated roads (cabañera). The beetle larvae then waited undisturbed in the soil of the cabañera until the next passage.

Nowadays, during winter, now that transhumancia is discontinued, the herds are grazing on the fields surrounding the villages. The beetles, it's in their genes, start building breeding chambers, stock them with dung and add eggs. Problem with this age-old scenario is that it's adapted to pastures. It's disastrous in fields. Fields need to be plowed and many brood balls, the protected environment of the larva, are damaged causing death of the young as a consequence. This could have an adverse effect on some populations.

The villages in the valley of Puértolas are mainly rural communities where it's easy to find sufficient amounts of manure. Samples were taken where the suppliers were, at lower altitudes during winter and higher up during the warmer months. It is possible to take a dropping and extract everything using a flotation method, but I choose to take a dropping, break it apart and grab the beetles with a pair of tweezers. That's certainly not good enough for a quantitative study, but it gives a good idea of the species composition (although very small and dark beetles could escape detection).

 Read our report