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Some of the most remarkable
beetles are the dung beetles, which spend almost their whole lives eating
and breeding in dung’.
More than 4,000 species of
these remarkable creatures have evolved and adapted to the world’s
different climates and the dung of its many animals. Australia’s native
dung beetles are scrub and woodland dwellers, specialising in coarse
marsupial droppings and avoiding the soft cattle dung in which bush flies
and buffalo flies breed.
In the early 1960s George
Bornemissza, then a scientist at the Australian Government’s premier
research organisation, the Commonwealth Scientific and Industrial Research
Organisation (CSIRO), suggested that dung beetles should be introduced to
Australia to control dung-breeding flies. Between 1968 and 1982, the CSIRO
imported insects from about 50 different species of dung beetle, from Asia,
Europe and Africa, aiming to match them to different climatic zones in
Australia. Of the 26 species that are known to have become successfully
integrated into the local environment, only one, an African species
released in northern Australia, has reached its natural boundary.
Introducing dung beetles into
a pasture is a simple process: approximately 1,500 beetles are released; a
handful at a time, into fresh cow pats 2 in the cow pasture. The beetles
immediately disappear beneath the pats digging and tunnelling and, if they
successfully adapt to their new environment, soon become a permanent,
self-sustaining part of the local ecology. In time they multiply and within
three or four years the benefits to the pasture are obvious.
Dung beetles work from the
inside of the pat so they are sheltered from predators such as birds and
foxes. Most species burrow into the soil and bury dung in tunnels directly
underneath the pats, which are hollowed out from within. Some large species
originating from France excavate tunnels to a depth of approximately 30 cm
below the dung pat. These beetles make sausage-shaped brood chambers along
the tunnels. The shallowest tunnels belong to a much smaller Spanish species
that buries dung in chambers that hang like fruit from the branches of a
pear tree. South African beetles dig narrow tunnels of approximately 20 cm
below the surface of the pat. Some surface-dwelling beetles, including a
South African species, cut perfectly-shaped balls from the pat, which are
rolled away and attached to the bases of plants.
For maximum dung burial in
spring, summer and autumn, farmers require a variety of species with
overlapping periods of activity. In the cooler environments of the state of
Victoria, the large French species (2.5 cms long) is matched with smaller
(half this size), temperate-climate Spanish species. The former are slow to
recover from the winter cold and produce only one or two generations of
offspring from late spring until autumn. The latter, which multiplies
rapidly in early spring, produce two to five generations annually. The
South African ball-rolling species, being a subtropical beetle, prefers the
climate of northern and coastal New South Wales where it commonly works
with the South African tunnelling species. In warmer climates, many species
are active for longer periods of the year.
Dung beetles were initially
introduced in the late 1960s with a view to controlling buffalo flies by
removing the dung within a day or two and so preventing flies from
breeding. However, other benefits have become evident. Once the beetle
larvae have finished pupation, the residue is a first-rate source of
fertiliser. The tunnels abandoned by the beetles provide excellent aeration
and water channels for root systems. In addition, when the new generation
of beetles has left the nest the abandoned burrows are an attractive
habitat for soil-enriching earthworms. The digested dung in these burrows
is an excellent food supply for the earthworms, which decompose it further
to provide essential soil nutrients. If it were not for the dung beetle,
chemical fertiliser and dung would be washed by rain into streams and
rivers before it could be absorbed into the hard earth, polluting water courses
and causing blooms of blue-green algae. Without the beetles to dispose of
the dung, cow pats would litter pastures making grass inedible to cattle
and depriving the soil of sunlight. Australia’s 30 million cattle each
produce 10-12 cow pats a day. This amounts to 1.7 billion tonnes a year,
enough to smother about 110,000 sq km of pasture, half the area of
Victoria.
Dung beetles have become an
integral part of the successful management of dairy farms in Australia over
the past few decades. A number of species are available from the CSIRO or
through a small number of private breeders, most of whom were entomologists
with the CSIRO’s dung beetle unit who have taken their specialised
knowledge of the insect and opened small businesses in direct competition with
their former employer.
Glossary
1.
dung:- the droppings or excreta of animals
2.
cow pats:- droppings of cows
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