What are dung beetles?

Introduction

Dung beetles are found on all the continents in the world except Antarctica and have evolved to feed and breed in dung. Scarabaeinae are often broadly classified into three broad functional groups based on dung nesting behaviour: dwellers (those that build nests in the dung and don’t burrow), tunnellers (species that burrow into the substrate beneath the dung to build nests) and rollers (dung beetles that relocate balls of dung carved from the dung heap to build nests). Tunnellers are by far the most diverse and abundant group, and are most often utilised for the rapid removal of fresh dung from pasture surfaces into the underlying soils.

Seasonal activity of dung beetles is variable between species with most being active in spring and summer. But there are species that also feed and breed in autumn and winter. Similarly, dung beetles can be categorised as either day active, night active, or active during dawn and dusk.

Virtually all dung beetles are very habitat specific. For example, those that occur only in forest habitats and those that have evolved in open grasslands often have little or no overlap. Many dung beetles specialise on particular types of dung. Beetles that are specific to both open grassland habitat and the dung of ungulate mammals (e.g. cows) are the ones targeted for dung beetle importation projects to bury livestock dung.

Life history

Dung beetles search out the faeces of animals which they use for food and reproduction. Most adult dung beetles make tunnels in the soil beneath the dung deposits to depths up to 90 cm depending on species, soil type and moisture content. Excavated soil is pushed to the surface forming soil casts underneath or at the edge of the dung pat. The beetles take the dung down into the tunnels to lay eggs in. Moderate to high densities of dung beetles can remove fresh dung from the pasture surface within 24-48 hours, leaving behind inedible sawdust-like dry material that is easily dispersed. As the eggs hatch the grubs feed on the dung until they are large enough to pupate. Any uneaten dung and the waste produced by the developing grubs is utilised by soil microbes and earthworms. Depending on the species and environmental conditions, a young adult beetle may emerge several weeks or months later. The entire life cycle may take as little as 6 weeks to complete or as long as a year, depending on the type of dung beetle and the climate it lives in.

A simplified lifecycle of a tunnelling dung beetle similar to those due for release in New Zealand. (Modified from Bornemissza 1976)

A simplified lifecycle of a tunnelling dung beetle similar to those due for release in New Zealand. (Modified from Bornemissza 1976)

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