SANDGROPERS
Adult sandgroper, Cylindraustralia kochii.
The term 'sandgropers' has a long history as a colloquial name for people born and raised in Western Australia. Less well known is its application to a group of unusual insects found in this state but not restricted to it. Because the insectan sandgropers spend virtually their whole lives underground, they have been difficult subjects for study and little was known about their biology until recently. They are familiar to farmers in the northern wheatbelt of Western Australia who have attributed severe crop and pasture losses to them (Richards 1980). In 2002, Terry Houston set out to try to learn at least the basic details of sandgroper biology and achieved considerable success. Pending publication of his results, only some general details are given here.
Sandgropers are moderately large insects, adults attaining lengths of 35-88 mm, depending on species. Their bodies are highly modified for burrowing, being very elongated and cylindrical with reduced appendages. Wings are entirely absent and the ‘compound’ eyes are reduced to simple eyes. The fore legs are highly modified for burrowing and no longer look like legs, being very short, strongly flattened and situated either side of the head. The mid and hind legs, situated nearer the middle of the body, are also comparatively small and recess into the sides of the body.
True to their name, sandgropers prefer sandy soils through which they can burrow easily. Some also inhabit sandy loams which can become hard when dry. The insects burrow by parting the soil ahead of them with breast-stroke-like motions of their very powerful fore legs, compressing the soil and creating an open gallery as they progress. They are able to run backwards or forward within these galleries on their mid and hind legs. Following rain, the insects commonly burrow long distances just beneath the surface of the ground, creating tell-tale raised ‘trails’.
Trails of sandgropers (across middle ground).
While sandgropers were once regarded as degenerate mole crickets, they have been shown to be more closely related to grasshoppers and locusts and are now classified within their own family, Cylindrachetidae, in the order Orthoptera (grasshoppers and crickets). Like their grasshopper relatives, sandgropers develop gradually from egg to adult (that is, juveniles resemble adults except for their smaller size).
Sixteen species classified into three genera were recognized in the most recent taxonomic study of the family (Gunther 1992): the genus Cylindraustralia was established for 13 Australian and one New Guinea species (all earlier placed in Cylindracheta), Cylindracheta is now restricted to one species from the ‘Top End’ of the Northern Territory, and Cylindrodes contains one Argentinean species. The genus Cylindraustralia is represented widely across the Australian continent from the west coast through the arid interior to western New South Wales and north-eastern Queensland. However, none occur in south-eastern Australia (including Tasmania). Six species are recorded from Western Australian and two of them, C. kochii and C. tindalei, inhabit the Perth region.
Rentz (1996) has provided the most recent popular account of the insects.
References:
Gunther, K.K. (1992). Revision der Familie Cylindrachetidae Giglio-Tos, 1914 (Orthoptera, Tridactyloidea). Deutsche entomologische Zeitschrift, N.F. 39(4-5): 233-291.
Rentz, D.C.F. (1996). Grasshopper Country -The abundant orthopteroid insects of Australia (University of New South Wales Press: Sydney).
Richards, K.T. (1980). The sandgroper - a sometimes not so friendly Western Australian. Journal of Agriculture Western Australia 21(2): 52-53.