Onthophagus taurus (Schreber, 1759)
Bull Dung Beetle
This very widespread native Palaearctic species is generally common and often abundant throughout much of its range; extending from Portugal east to China (Xinjiang province) and including much of north Africa and the Middle East; Iran, Iraq, Egypt, Israel, Morocco, Tunisia, Algeria and Libya etc. and the Mediterranean islands. To the north it extends into Scandinavia but there are only historical records from the U.K.; a female was found in Brockenhurst (South Hants.) in October 1824, a pair was recorded from Oxford pre-1841 and there is a pre-1867 record from Exmouth. A much more recent record from the New Forest in 1967 is thought to be unreliable. Whether these records are from accidental introductions, immigrants or the remnants of native populations can only be speculated upon. The species is also known from the U.K. fossil record; there are several Holocene specimens in the Hope collections in Oxford although one of these has been re-identified as the closely similar O. illyricus (Scopoli, 1763), another widespread but more northerly European species. Beyond its natural range it has been introduced into Australia, Canada and New Zealand for use in the burial of dung and the control of dung-breeding pests on pastures, and following its discovery in 1971, it is now widespread in the U.S.A.; it is adventive in much of Florida, Texas, New Hampshire and Minnesota, and has been intentionally introduced to California.
The adults are active from early spring to late autumn with peaks of activity in April, June/July and September; they pair up in the spring and, after mating, excavate a branched nesting gallery below a suitable dung sample; fresh and firm to liquid cattle dung is preferred but they will also choose fresh sheep dung, and they seem to have no preference regarding soil type. Galleries begin at about 10 cm below the surface and as each is excavated it is provisioned with a ‘brood sausage’ of dung into which a single egg is laid, sometimes the beetles are present in large numbers and so competition for dung is intense, and under these conditions each chamber will be tightly packed with dung samples. Pupation occurs in the chamber and fresh adults
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ascend the burrow to disperse, development is rapid and under optimum conditions of nutrition and temperature the cycle from egg to adult takes eight to ten weeks, there are often two generations each year and in warmer climates this is the norm. Well fed and later instar larvae will overwinter in the brood chamber, continuing to feed in mild spells and producing very early spring adults. Those that eclose and emerge in the autumn will return to the burrow to overwinter, occasionally surfacing in mild spells to feed, in milder climates therefore the adults may be found year-round.
Relatively large; 8-10mm and uniformly black to dark reddish-brown but for the tarsi and the antennal funiculus which vary from dark to pale brown. The species exhibits extreme sexual dimorphism; in males the anterior transverse ridge on the vertex of the head is produced laterally into long curved horns which are used in sexual competitions, in the female this ridge is not produced. Larger males have larger horns whereas small males do not possess horns and remain non-aggressive; instead the genitalia tend to be better developed. Eyes large in dorsal aspect, clypeus produced; rounded in females, more angled anteriorly in males. Entire surface of the head and pronotum finely and diffusely punctured, the head a little more densely so. Pronotum rounded, without hind angles; anterior angles produced and the margin posterior to this straight, not sinuate. Scutellum hidden beneath the pronotal hind margin. Elytra with weakly impressed but distinct punctured striae, the interstices are variously convex, often only weakly so. Epipleura wide and strongly bordered to the outer apical angle. Legs very robust, especially the femora; pro-tibiae with large lateral teeth which are broader in the female but soon become worn, meso- and meta-tibiae narrower and with finer lateral teeth and transverse ridges. All tibiae with a well-developed spur on the inner apical angle. The pro-tibiae are fossorial, the meso- and meta-tibiae evolved to push the beetle forward while digging. Tarsal formula 5-5-5; all tarsi long and slender, the pro-tarsi much smaller.