Cow pats

The World of the Rannoch Cow Pat — A Hidden Kingdom

What appears to be nothing more than a casual deposit on the grass is, in truth, one of the most dynamic, vital, and rapidly changing ecosystems in the Rannoch landscape — a rich, temporary island of fertility that connects the grazing herds to the soil, the plants, and the wider food web. Each fresh pat begins as a moist, fibrous mass, warm from the animal, and within minutes of being dropped it is already under colonisation — a pulse of life that unfolds in days rather than years, and one that quietly drives the health of the whole glen.

The Dung Beetles — The Architects & Recyclers

These are the most visible and influential inhabitants, arriving almost before the cow has walked away. In the Rannoch area, several species are reliably found, each with its own lifestyle and role:

• Aphodius dung beetles — the most numerous and diverse group. Aphodius fossor, large, glossy black and abundant across the Highlands, digs vertical tunnels directly beneath the pat, dragging dung down to lay its eggs in safety. Aphodius rufipes, dark with reddish wing‑cases, is common on the moors and active late into autumn, while Aphodius ater, smaller and jet‑black, appears in spring and early summer. All are "dwellers" — their larvae grow up within the dung itself, feeding and breaking it down from within.

• Geotrupes stercorarius — the Common Dor Beetle, a large, deep bronze‑black beetle that buzzes loudly in flight and digs deep vertical shafts beneath the pat, burying great lumps of dung to feed its young many centimetres below the surface. In doing so, it aerates the soil, cycles nutrients deep into the earth, and creates ready‑made burrows used by other creatures. Its relative Geotrupes spiniger, slightly smaller and greener, is also found on the richer pastures around the loch.

• Onthophagus joannae — a tiny, compact black beetle, a "roller" that fashions small balls of dung and rolls them away to bury nearby, common on the drier, grassier slopes.

• Anoplotrupes stercorosus — the Woodland Dor Beetle, found where cattle graze near birch and pine, particularly around the Black Wood of Rannoch.

Together they are not just cleaning up — they are mining nutrients from the grass and returning them to the soil, making them immediately available to new growth. A single pat can be completely dispersed and buried by beetles in as little as two to four weeks in warm weather.

The Flies — The Rapid Generations

Scatological flies are the fast‑breeding pioneers, turning dung into new life with astonishing speed:

• Scathophaga stercoraria — the Yellow Dung Fly, the most familiar and iconic of all. The males are brilliant golden‑yellow and furry, hovering over the pat in sunshine; the females are duller and darker. They arrive within minutes, lay their eggs in the freshest dung, and their yellow, worm‑like maggots consume it rapidly before pupating in the soil. They are also formidable predators — the adults hunt smaller insects on the dung surface, making them both decomposers and hunters.

• Sepsis species — the "small dung flies", slender, black, and delicate with a distinctive rapid, jerky walk across the dung surface. Sepsis cynipsea and Sepsis violacea are common throughout the Highlands. They are tiny but incredibly numerous, and their larvae help break down the finer, moister fractions of the dung.

• Musca autumnalis — the Face Fly, similar to the common house fly but associated almost entirely with cattle dung; its larvae develop rapidly in fresh pats.

• Haematobia irritans — the Horn Fly, smaller and blood‑sucking as an adult, but its larvae live and develop within the dung — a reminder that the pat is both nursery and home.

Parasites — The Hidden Web

The cow pat is also the stage for a complex and largely invisible relationship between host, parasite, and insect — one that has existed for millennia:

• Nematode worms — the gastrointestinal roundworms such as Ostertagia ostertagi, Cooperia, and Nematodirus — shed their eggs in the dung, where the larvae hatch, develop, and migrate out onto the surrounding grass to be eaten again by grazing animals. This is the natural cycle, kept in balance by immunity and low stocking densities.

• Dung beetles and flies — far from being victims, they often help control parasites: beetles burying dung bury many larvae too; fly maggots physically disturb and consume some nematode eggs; and the drying and fragmentation of the pat speeds up the death of vulnerable parasite larvae.

• Bot flies — Hypoderma species, whose larvae pass through the dung before pupating in the soil — increasingly rare but still occasionally seen in the glen.

In a healthy, unpoisoned system, the insects and the parasites are in constant competition — the beetles and flies breaking up the dung and disrupting the parasite life cycle.

The Threat — Veterinary Pesticides & Endectocides

This entire, intricate world is extraordinarily vulnerable — and the greatest threat comes not from development or drainage, but from within the herd itself. Modern veterinary medicines, particularly the widely used ivermectin and related compounds (doramectin, moxidectin), are powerful insecticides that pass largely unchanged through the animal’s gut and are excreted in the dung. They are highly effective against internal parasites, but they remain active in the pat for up to several weeks — and they are lethal to the very creatures that break the dung down.

• Dung beetles arriving at a pat from a recently treated animal will die or fail to reproduce. Even sub‑lethal doses stop them feeding, tunnelling, or laying eggs.

• Fly maggots — especially the yellow dung fly — are extremely sensitive; even low concentrations prevent development entirely.

• The result — the pat remains intact and undecomposed for months rather than weeks, standing like a hard, dry mound that releases no nutrients back to the soil. It becomes a "dead island" — rich in energy but locked away, and the pasture around it dies back because the grass will not grow up through the hard, unbroken surface.

• Worse still — with no beetles or flies to disturb them, parasite survival actually increases, because their dung‑dwelling competitors and predators are gone. The very medicine intended to help the animal can, over time, make the pasture more infective.

Other compounds — synthetic pyrethroids used in pour‑ons, and some anthelmintics — have similar though generally milder effects. The scale of the loss is hard to see, because it happens one pat at a time — but across a moor, across a glen, it amounts to the silent collapse of the dung‑decomposer food web.

The Wider Community — What Else Lives There?

Beyond beetles and flies, the cow pat feeds and supports a surprising cast of characters:

• Rove beetles — fierce, elongated predators that run across the dung surface hunting fly eggs and small larvae; Philonthus and Staphylinus species are common.

• Ladybirds, spiders, and ants — come to feed on the abundant small insects that gather there.

• Gulls, crows, and starlings — peck apart the dung to reach the beetle grubs and larvae; in winter, the thrushes and fieldfares do the same.

• Mites — microscopic travellers that cling to dung beetles and flies, hitching a ride to fresh pats and eating fungal spores and nematode eggs.

• Fungi — the "cap mushrooms" that appear around old pats, such as the Panaeolus and Coprinus species, break down the remaining fibres and return the last nutrients to the soil.

Summary — A Cycle of Renewal

Each cow pat dropped in Rannoch is — colonised within hours, transformed within weeks, and gone within a month, its energy passed through beetles, flies, mites, fungi, and birds back into the grass and soil. It is one of the fastest, most efficient nutrient cycles in the whole landscape — and it is entirely dependent on the beetles and flies to work. Where veterinary medicines are used thoughtfully, the balance holds; where they are over‑used, the pat becomes a silent, dead monument — and the whole web frays. To look closely at a cow pat in Rannoch is to see the whole ecosystem in miniature: the grazing animal, the soil, the insects, the birds, and the plants — all connected by a cycle that is vital.