The Striped Legless
Lizard
Delma impar
Photo: Bob Beukers
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Summary
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Taxonomy
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Description
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Distribution
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Population Status
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Habitat and Ecology
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Threats to Survival
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Conservation Measures Taken
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Conservation Measures Proposed
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Current Research
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Literature Cited
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Source
The Family Pygopodidae is endemic to Australia and New Guinea with closest affinities to the gecko lizards. They are snake-like in appearance, differing in gross external morphology from the snakes by the usual presence of an ear opening, a fleshy tongue, and a tail that is as long or longer than the body itself.
The Striped Legless Lizard, Delma impar, was first described in 1882 from a specimen collected in Victoria, but unfortunately this specimen no longer exists. Its current range includes the basalt plains to the west of Melbourne, a number of areas within the Australian Capital Territory (ACT), as well as areas around Ballart and Bendigo.
D. impar typically has a base colour of pale grey-brown with, as the common name suggests, a number of dark brown or blackish dorso-lateral and lateral longitidinal stripes which start from the neck and cover the length of the body and tail. These stripes often have a white edging. The dorsal surface of the head may be slightly darker than that of the body, whereas the ventrum is typically white, cream or pink.
Delma impar inhabitats lowland native grasslands, typically dominated by native tussock forming grass species. Such species include kangaroo grass (Themeda triandra) as well as spear grass (Stipa bigeniculata). The species was once relatively widespread in the native grasslands of south-eastern Australia but has suffered a substantial contraction in geographic range and abundance over the past 100 years . With the continued fragmentation and modification of lowland native grasslands inhabited by D. impar, the threatened status of this species is formally recognized in a number of forums.
Delma impar feeds only on invertebrate prey and may be considered as a selective arthropod feeder. While the predominant prey types of the species in Victoria were found to be crickets and noctuid moth larvae, spiders were found to be the predominant prey type within the ACT. Wolf spiders (Lycosidae) are the most common spider family consumed while jumping spiders (Salticidae) also occurr. Other main prey types of the species include cockroaches and grasshoppers, with the occassional occurrence of beetles, flies and ants within the diet .
Little is known of the reproduction of D. impar. It is likely that the species ovulates during spring and ealy summer, followed by egglaying in mid summer. The eggs are characteristically elongate in shape. Each clutch contains two eggs, as with the geckoes, and takes five to eight weeks to hatch. The eggs are soft shelled and approximately 2 cm in length, swelling to approximately 3 cm in length while incubating.
In 1988, concern for the status of D. impar became more focussed in Victoria with the formulation of the Striped Legless Lizard Working Group by the Department of Conservation and Natural Resources. This group provides a point from which research and management can be co-ordinated.
The declaration on 8-Aug-89 of the Derrimut Grassland, 15 km to the west of Melbourne and is approximately 152 hectares in area , provides the only conservation reserve known to support a population of D. impar and is therefore central to the efforts which are being made to aid in the survival of this species.
Within the ACT extensive survey work has been carried out since 1989 and has isolated a number of areas which support populations of D. impar, though none yet reside in reserves.
Legless Lizards of the Family Pygopodidae are endemic to Australia and New Guinea. While serpentine in appearance, this lizard family is considered to be more closely related to geckoes than to any other saurian family (Kluge 1976). Currently 35 species of pygopodidae are recognized and have been placed within eight genera.
Delma impar was originally described as Pseudodelma impar in 1882 by J.G. Fischer based on a holotype collected in 1881 in Melbourne, Victoria, by K. or G. Semper. It was probably lodged with the Staatliches Museum fürTierkunde in Dresden, and destroyed in the bombing of Dresden during World War II (Kluge 1974).
In 1905, Rosén claimed to have found a new species which was closely related to Pseudodelma impar and named it Delma lineata (Cogger et. al. 1983), however the characteristics of D. lineata described by Rosén were also frequently observed in P. impar and the two were synonymized by Kluge (1974) and subsequently included in the Delma genus as Delma impar.
Kluge (1974) listed a number of diagnostic characters which, in combination, distinguish D. impar from all other members of the genus. These include the fused state of nasal and supralabial scales to the nostril; the presence of five or six loreal scales; five anterior orbital scales; generally four frontal scales; the fourth supralabial below orbit; usually ten nuchal scales and twelve gular scales. Specimens examined by Coulson (1990) revealed that the main diagnostic feature of partly fused nasal and supralabial scales was not always present for all individuals.
D. impar has an elongate body form and an almost snake-like appearance, in common with other members of its Family. However, this physical similarity is less striking after a second glance, which reveals several characteristic legless lizard features. Delma impar has a fleshy tongue and an external ear opening, traits which are not shared by snakes. Furthermore, all legless lizards possess hind limbs, which are reduced to short, scaly flaps that lay neatly along the body at the base of the tail. It is unclear if if these flaps serve any real purpose, although it has been suggested that they may be utilised during courtship or mating (Greer 1989), while observations of captive D. impar have shown that flaps may be extended when the species is handled or agitated.
D. impar has a base colour of pale grey-brown with, as the common name suggests, a number of dark brown or blackish dorso-lateral and lateral longitidinal stripes which start from the neck and cover the length of the body and tail (Cogger 1992). These stripes often have a white edging. The dorsal surface of the head may be slightly darker than that of the body, whereas the ventrum is typically white (Coulson 1990), cream (Jenkins and Bartell 1980) or pink (Nunan, pers. obs.). In some individuals, the yellow of the infralabial and adjacent gular scales extends back to the tympanum. There is no evidence of rapid colour change in life (Coulson 1990). Although conspicuous stripes are considered as a distinguishing feature of the species (Kluge 1974), these stripes may be pale (Coulson 1990) or almost completely absent (Nunan, pers. obs.).
Unlike the adults, D. impar hatchlings lack any longtitudunial body stripes. However, they do have a characteristic dark brown or black head. It is possible that such markings are intended to mimic those of snakes, such as the juvenile eastern brown snake (Greer 1989). This dark colouration fades with age.
Species of the Delma genus are generally considered to be of average size by legless lizards standards. Delma impar may grow to approximately 30 cm in length, with an average adult body weight of 4.1 g (Coulson 1990). The tail is surprisingly long, and may contribute up to two thirds of the total body length. In common with their nearest living relatives, the geckoes, pygopodids have a voice box and may emit a high pitched squeak when handled or distressed. What function this voice serves in the wild is unknown, though it may be used to startle predators, or as a form of communication during mating, courtship and aggressive encounters.
Sexual dimorphism is shown in the number of ventral scales, with males possessing more scales on average than females (Kluge 1974, Coulson 1990). However, Handley (1994) found that females possessed more scales on average than males, and suggested that ventral scale counts may be of use only if all specimens are from the same region. The technique of radiography to test for the presence of post cloacal bones, which only males possess, has been found to be the most successful sex determination tool (Handley 1994).
Historically, the species have been recorded from around 250 sites, which cover an area from south eastern South Australia across to the western and central districts of Victoria and through New South Wales to the ACT (Hadden 1995). Numerous years of survey work have revealed that many of these sites are no longer considered to support populations of D. impar. In recent times, D. impar has only been recorded at 40 of these 250 sites (Hadden 1995). Currently occupied sites are centered around the basalt plains to the west of Melbourne, a number of areas within the ACT, as well as areas around Ballart and Bendigo.
D. impar has suffered a substantial contraction in geographic range and abundance over the past 100 years (Coulson 1990) and was once relatively widespread in the native grasslands of south-eastern Australia (Delma Working Group 1994). With the continued fragmentation and modification of lowland native grasslands inhabited by D. impar, the threatened status of this species is formally recognized in a number of forums.These include:
- Listed as a nationally vulnerable species by the Australian and New Zealand Environment Council,1991.
- Listed as a species endangered, vulnerable or threatened with extinction on Schedule 1 of the Endangered Species Protection Act 1992 (Commonwealth).
- Listed as a species vulnerable to or threatened with extinction with Special Protection Status on Schedule 6 of the Nature Conservation Act 1980 (ACT).
- Listed as threatened taxa on Schedule 2 of the Flora and Fauna Guarantee Act 1988 (Vic.)
- Listed under vulnerable and rare species on Schedule 12 of the National Parks and Wildlife Act 1974 (NSW).
- Listed as a vulnerable species by the IUCN-World Conservation Union: Red List of Threatened Animals, 1994.
Delma impar inhabitats lowland native grasslands, typically dominated by native tussock forming grass species (Delma Working Group 1994). Such species include kangaroo grass (Themeda triandra) as well as spear grass (Stipa bigeniculata). Grassland areas dominated by introduced species of tussock forming grasses have also been known to support numbers of D. impar (Kukolic et al. 1994), although it is unclear as to whether such areas provide the species with suitable long term habitat.
Within Victoria, the native grassland habitat of the species typically occurs on deep cracking clay soils with volcanic rocks scattered about the surface. Cracks in the soil may be extensive in these areas and are considered important in providing shelter from fire and predators, as well as a place to lay eggs (DCNR 1995). Rocks are also commonly used as refuge.
When comparing these Victorian attributes of D. impar habitat against those in the ACT, geographic variation is apparent. Grasslands in the ACT generally lack extensive cracks in the soil, with rocks, logs and any other surface debris generally uncommon. It is not known if any behavioural, physiological or ecological differences occur between the populations in these two areas as a result of these habitat differences. Very litle is actually known on how habitat is utilised by D. impar. It has been suggested that the lizards may over-winter at the base of grass tussocks, or possibly under the ground surface or thatch cover (Delma Working Group 1994). Within the ACT D. impar does utilise any cracks that are found in the soil, with eggs occasionally found down the side of pitfall traps which have been sunk into the ground (Nunan, pers. obs.). However, considering the lack of available shelter, it seems likely that within the ACT eggs are laid at the base of grass tussocks.
Little is known on the reproductive parameters of D. impar however it is considered probable that the species ovulates during spring and ealy summer, followed by egglaying in mid summer. The eggs are characteristically elongate in shape. Each clutch contains two eggs, as with the geckoes, and takes five to eight weeks to hatch (DCNR 1995). The eggs are soft shelled and approximately 2 cm in length, swelling to approximately 3 cm in length while incubating.
No research has been undertaken into the age at which sexual maturity is reached, nor the longevity or survivorship of individuals. Lizards held in captivity have provided some information, surviving up to four years and eight months (ACT Parks and Conservation, unpublished data) However it is difficult to ascertain whether captive survival is indicative of that in the wild.
Delma impar feeds only on invertebrate prey and may be considered as a selective arthropod feeder (Nunan 1995). While the predominant prey types of the species in Victoria were found to be crickets and noctuid moth larvae (Wainer 1992), spiders were found to be the predominant prey type within the ACT (Nunan 1995). Wolf spiders (Lycosidae) are the most common spider family consumed while jumping spiders (Salticidae) also occurr. Other main prey types of the species include cockroaches and grasshoppers, with the occassional occurrence of beetles, flies and ants within the diet (Nunan 1995).
Delma impar individuals have the ability to drop their tail. The proportion of the tail which a lizard drops may vary from just the tip, to the entire tail up to the vent. Considering that a majority of the total body length consists of tail, in cases where the entire tail was dropped, only a small portion of the original lizard would remain. This may be considered as a useful tool for avoiding predation. Individuals that have lost their tail are obvious, as body stripes are only uniform and continous along the length of the body for individuals with their original tail.
Native temperate grasslands are one of the most endangered ecosystems in Australia (McDougall and Kirkpatrick 1994) with lowland native grassland now only remaining as isolated remnants throughout the country (Sharp 1994). Preferred grassland habitat of D. impar is generally flat and relatively treeless, making such areas highly suitable for development and agriculture. Within the ACT, the plains which are now extensively occupied by the urban development of Canberra once supported treeless grasslands (Osborne et. al. 1994) which were most likely inhabited by D. impar. Such losses of suitable habitat remain the greatest threat to the survival of this species, resulting in local extinctions from historically occupied areas.
Further threats to the species are associated with the fragmetation of grassland areas and their modification. Contributing factors include ploughing, the application of fertiliser, pasture improvement, grazing, cropping and the invasion of exotic species (Delma Working Group 1994). Considering the susceptability of grassland to fire, when situated close to urban areas, and the small size and isolation of many grasslands supporting D. impar, fire also poses a serious threat to the species. It is thought that individuals may burrow into the soil, retreat into cracks, or shelter within tussocks or litter during fire. However this may only be possible if the fire is cool enough to leave some vegetation unburnt or that the soil conditions are dry enough to provide cracks.
Little is known on the extent and impacts of predation upon D. impar. However, the encroachment of urban development would most certainly place more predatory pressure on the species. Powerlines and poles may provide increased perching or surveillance opportunites for birds of prey while urban development would introduce more cats into the area (Delma Working Group 1994) which may also prey upon the species.
Within the ACT extensive survey work has been carried out since 1989 (Delma Woring Group 1994) and has isolated a number of areas which support populations of D. impar. Survey work in Victoria at a number of locations has also been undertaken, revealing remnant populations of the species (DCE 1992b).
In 1988, concern for the status of D. impar became more focussed in Victoria with the formulation of the Striped Legless Lizard Working Group by the Department of Conservation and Natural Resources. This group provides a point from which research and management can be co-ordinated.
The declaration of the Derrimut Grassland on the 8th August 1989 was a significant step in the direction of conservation for this species. This reserve is 15 km to the west of Melbourne and is approximately 152 hectares in area (DCE 1992a). Derrimut is the only conservation reserve known to support a population of D. impar (DCE 1992b) and is therefore central to the efforts which are being made to aid in the survival of this species.
To increase public awareness of the plight of this species, and in consideration of the close proximity of many populations to urban development, a pamphlet was published by the Department of Conservation and Environment (DCE) in 1991. This outlined the threats to the survival of D. impar as well as how the general community could participate in the conservation initiative. A poster was also published by DCE in 1991 on the grasslands in Victoria featuring D. impar. Further public participation in the conservation of this species has been encouraged through the formulation of the 'Friends of Delma' group which was established in 1991.
A draft conservation strategy for D. impar in the ACT was released in 1994 and outlines the need for further survey work within the ACT and surrounding NSW to pinpoint the conservation value of sites threatened by development (Delma Working Group 1994). Specific species and habitat attributes requiring research attention were also identified in this report. An action statement was released in 1992 by the Department of Conservation and Environment which outlined issues associated with the conservation and management of D. impar in Victoria (DCE 1992b). Action Statements are designed to enhance populations and habitat conservation in the wild (Mansergh et. al. 1993). Proposed management actions were outlined in the Action Statement, with implimentation to be specifically undertaken by the Striped Legless Lizard Working Group.
The protective legislation in place on a state, commonwealth and international level should ensure that D. impar receives continued conservation attention and that action is taken to remove any remaining threats to the species in areas known to support populations. Further survey work and continued monitoring of previously established sites is to be undertaken in the coming season within the ACT (Wildlife Research Unit pers. comm.1995) and should provide further information on the sustainability and stability of fragmented populations. While the need to conserve areas that support populations of D. impar has been identified, no such conservation areas currently exist within the ACT. Considering the close proximity of many popuilations of D. impar to urban development, such a conservation measure should maintain high priority.
Published papers are few and knowledge of the biology and ecology of this species remains limited. However, there have been a number of recent research projects undertaken in an effort to improve this knowledge and further assist with the management and conservation of the species. Research on the metabolism, genetics and temperature preferences of the species was undertaken by Osmond (1994), microhabitat selection and mobility has been examined by Kutt (1992) and Dorrough (1995) investigated the past and present habitat parameters of the species within the ACT. Preliminary dietary studies in Victoria were undertaken by Wainer (1992) and Coulson (1992) while Nunan (1995) examined the diet and feeding ecology of D. impar in the ACT in more detail.
Further research is required into specific areas such as the impacts of fire, urban development, grazing and predators, such as foxes and free-ranging companion cats. Research into the mobility and movement patterns of the species is also urgently required, but is hampered by the body form and habitat of the species. Tracking the lizards with fluorescent dye has not been particularly successful with flurescent powder rubbing off relatively quickly (Kutt 1994). While radio transmitters would interfere with the streamlined body form of the species, size constraints also inhibit its use. Until an effective tracking method is determined for this species, many questions remain unanswered on the daily and seasonal movement patterns of individuals.
Cogger, H.G. 1992. Reptiles and amphibians of Australia. Reed Books, Chatswood, Australia.
Cogger, H.G., Cameron, E.E. and Cogger, H.M. 1983. Zoological Catalogue of Australia 1 Amphibia and Reptilia. Australian Government Publishing Service, Canberra.
Coulson, G. 1990. Conservation biology of the striped legless lizard (Delma impar): an initial investigation. ARI Technical Report Series No. 106, Department of Conservation and Environment, Melbourne, Australia.
DCE (1992a). Derrimut Grassland Reserve draft management plan. Department of Conservation and Environment, Melbourne, Victoria
DCE (1992b). Striped legless lizard Delma impar. Action Satement No. 17. Department of Conservation and Environment, Victoria.
DCNR (1995) Striped legless lizard: managing a threatened species in our native grasslands. Pamphlet released the Department of Conservation and Natural Resources, Victoria. March, 1995.
Delma Working Group. 1994. Conservation strategy for the striped legless lizard Delma impar in the Australian Capital Territory. Unpublished report to the Minister for the Environment Land and Planning, October 1994, Canberra, Australia.
Dorrough, J. 1995. Past and present habitat of Delma impar within the ACT. Unpublished Honours Thesis. Australian National University, Canberra.
Greer, A.E. 1989. The biology and evolution of Australian lizards. Surrey Beatty & Sons, Chipping Norton, Australia.
Hadden, S. 1995. Distribution, population habitat estimates and habitat requirements of the striped legless lizard Delma impar (Fischer). Unpublished report to the Australian Nature Conservation Agency, Melbourne, Australia.
Handley, K. 1994. Methods for sexing live specimens of Delma impar. Department of Zoology, University of Melbourne.
Jenkins, R. and Bartell, R. 1980. Reptiles of the Australian high country. Inkata Press, Melbourne, Australia.
Kluge, A.G. 1974. A taxonomic revision of the lizard family Pygopodidae. Miscellaneous Publications, Museum of Zoology, University of Michigan 147: 1-221.
Kluge, A.G. 1976. Phylogenetic relationships in the lizard family Pygopodidae: an evaluation of theory, methods and data. Miscellaneous publications, Museum of Zoology. University of Michigan, No. 152.
Kukolic, K. 1994. Survey for the striped legless lizard Delma impar during 1993 at the National Museum of Australia site, Yarrumundi Reach, ACT Report to the National Capital Planning Authority, December 1994. Wildlife Research Unit, ACT Parks and Conservation Service, Canberra, Australia.
Kukolic, K. McElhinney, N. and Osborne, W.S. 1994. Survey for the striped legless lizard Delma impar during 1993 in the proposed development area E1 comprising sites for the Gungahlin town centre and the suburb of Franklin. Internal Report 94/3, May 1994. Wildlife Research Unit, ACT Parks and Conservation Service, Canberra, Australia.
Kutt, A.S. 1992. Microhabitat selection and mobility of the striped legless lizard, Delma impar. Unpublished honours thesis, Department of Zoology, University of Melbourne, Melbourne, Australia.
Kutt, A.S. 1994. A preliminary evaluation of the use of fluorescent pigments to track the movements of the striped legless lizard Delma impar (Reptilia: Pygopodidae). Pages 179-183 in S. Lunney and D. Ayers, editors. Herpetology in Australia. Transactions of the Royal Zoological Society of NSW, Sydney, Australia.
Mansergh, I., Davey, G. and Robertson P. (1993). Reptiles and amphibians of Victoria--legislation. In Lunney, D. and Ayers, D. (editors). Herpetology in Australia: a diverse discipline. Royal Zoological Society of New South Wales,. Mosman.
McDougall, K. and Kirkpatrick, J.B., editors. 1994. Conservation of lowland native grasslands in south-eastern Australia. World Wide Fund for Nature, Sydney, Australia.
Nunan, D.L. (1995). Diet and feeding ecology of the striped legless lizard Delma impar (Fischer 1882) within the Australian Capital Territory. Unpublished report to the ACT Parks and Conservation Service. July 1995.
Osborne, W.S., Kukolic, K. and Williams, K.D. 1994. Conservation of reptiles in the southern tablelands of New South Wales and the Australian Capital Territory. Pages 151-158 in S. Lunney and D. Ayers, editors. Herpetology in Australia. Transactions of the Royal Zoological Society of NSW, Sydney, Australia.
Osmond, H. 1994. Habitat specialisation and isolation of remnant populations of the striped legless lizard, Delma impar (Pygopodidae). Temperature preference, metabolic and allozyme correlates of activity in lizards with particular reference to fossorial habit. Unpublished honours thesis, Division of Botany and Zoology, Australian National University, Canberra, Australia.
Sharp, S. 1994. Lowland native grasslands in the ACT and surrounding region: a review and research strategy for a recovery plan. Technical paper 8. ACT Parks and Conservation Service, Canberra, Australia.
Wainer, J.W. 1992. Diet of the striped legless lizard, Delma impar, at the Derrimut Grassland Reserve, to the west of Melbourne. Unpublished repo+rt for the Department of Conservation and Environment, Melbourne, Australia.
This article was prepared by
Donna Nunan [Institute for Applied Ecology], based on a review of the literature in preparation
for her honours thesis.
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Applied
Ecology Research Group
