20/11/2025
The south-western Carpet Python was first described as a subspecies (Python spilotus imbricatus), based on specimens collected by the Western Australian Museum (Smith, 1981). The name imbricatus is derived from the Latin word imbricate, the way in which roof tiles overlap. Smith also used the word Lanceolate to describe the pointed shape, in addition to their overlapped nature, particularly the posterior dorsal scales. It was later given full species status, as Morelia imbricata.
The South-western Carpet Python occupies what is quite possibly the largest range among any of the Morelia clade. They are found as far north as Geraldton WA, occupying the Wheatbelt region and as far east as Kalgoorlie. From Geraldton, the South-western Carpet Python inhabits almost the entire coastline to the Eyre Peninsula of South Australia. Records published on the Atlas of Living Australia, Inaturalist and AROD (Australian Reptile Online Database) indicate that only the Nullarbor plain remains unoccupied by this large python species, at least within the parameters of their coastal orientated distribution. Isolated populations of Morelia imbricata also inhabit a number of islands and archipelagos adjacent to both WA and SA, these island localities will be covered in a later article.
For the purpose of this project, the present author has chosen to map mainland populations in two distributions, separated by the karst landscape of the Nullarbor region. The western distribution, accounts for mainland populations of Morelia imbricata across WA. Whilst the eastern distribution represents Morelia imbricata found throughout the Eyre Peninsula, as far north as Port Augusta and seemingly restricted to the coastline moving west.
Although both distributions remain genetically and phenotypically indistinguishable, limestone analysis of the Nullarbor and its cave systems give an insight into the development of this region and their disjunction some 1,000,000 years ago. Using information from these sediment studies, in addition to DNA sequencing of the Morelia clade, we might gain an understanding of the separation between populations on the east and west of this arid region.
During the Oligocene (35-25 ma), monsoonal woodland likely covered the Nullarbor Plain, with the warm climate supporting rainforests along waterways, similar to those seen in the Northern Territory today, (Webb, James 2006). The Oligocene-Miocene (23 ma) interval saw the development of shallow lakes across central Australia, (Alley et al, 1995). Biogeographic reconstruction of python taxon using an anchored hybrid enrichment approach indicates that by the early Miocene (21 ma), an ancestral form of the Morelia clade had arrived and begun to diversify across Australia, (Esquerré et al, 2020). By now, temperatures were rising and like much of Australia, the Nullarbor region had began to dry out. Vegetation shifted from monsoonal to open woodland as much of the rainforests diminished, leaving only remnants of rainforest-like vegetation, restricted to the valleys that continued to maintain a wetter climate, (Alley et al, 1995). By the beginning of the Pliocene (5 ma), The Nullarbor and its vegetation reflected much of what can be found today, with the addition of dry eucalypt woodland which likely covered a majority of the plain, (Webb, James 2006). Reviewing the same biogeographic reconstruction published in 2020, data indicates that the early Pliocene (10 ma) marks the breakaway for Morelia imbricata from the rest of the clade, (Esquerré et al, 2020). Further aridification by 1 Ma (1,000 Ka or 1,000,000 years ago) saw the Nullarbor region achieve its current level of dryness, as the first of Central Australia’s sand dunes were forming, (Chen, Barton, 1991)(Short et al, 2024). The following 974,000 years saw the development of clifftop sand dunes across the Nullarbor and much of Australia’s southern coastline, (Short et al, 2024). However, as the planet cooled, experiencing its Last Glacial Maximum (LGM) around 26-20 Ka, significant amounts of water formed frozen glaciers across much of the northern hemisphere. As a result, global sea levels were estimated to be 118m – 135m lower than present levels, (Clark, Mix, 2002). This estimate uses a minimum and maximum model, based on glacial reconstructions of ice sheets that are either restricted to continental margins (minimum model). Or significantly expanded marine-based ice sheets, which are used to identify a maximum model. As the planet slowly warmed, glaciers melted and sea levels began to rise, marking the end of the last ice age. Between 15 Ka and 8 Ka (a 7,000 year gap), sea levels rose by 100m as a result of glacial ice melt, (Williams et al, 2018).
This gives an indication of the timeline for Morelia imbricata’s break away from the clade, around 10 Ma (10,000,000 years ago), over the following 9.9 Ma (9,970,000 years) they most likely inhabited Western Australia. An understanding of their dispersion across Nullarbor and into South Australia is difficult to ascertain without more information. We could speculate that they inhabited the Nullarbor until its eventual arridification (1 Ma), but the likely alternative occurred much later. Significantly lower sea levels and a cooler climate during the LGM (26-20 Ka) would have provided an opportunity for dispersion across the Nullarbor plain and exposed coastline. Palaeo-vegetation records and Koala fossil records from 23 Ka to 5 Ka, show an increase in eucalyptus suitability throughout the Nullarbor, and Central Australia, (Shabani, 2019). Those same records describe a significant decrease in eucalyptus suitability over the past 5,000 years (5 Ka to present). This leads me to speculate that the two mainland distributions of South-western Carpet Pythons have only been truly separated within this past 5,000 years.
Despite the years apart, anecdotal observations of South-western Carpet Pythons, photographs and descriptive reports indicate very little distinction in phenotype between the separated distributions. Both present the same characteristic lateral stripe along the anterior of their bodies, a trait most commonly shared with Morelia spilota mcdowelli, Morelia spilota metcalfei and in some cases Morelia bredli. As with every other member of the clade, Morelia imbricata exhibit a significant variation in phenotype, not only in pattern, but in colour as well. Although, unlike others in the Morelia clade, the South-western Carpet Python’s variation in colour seems to reflect the region they inhabit, (Browne-Cooper, 2007). After much time spent analysing an updated record (since 2007) of phenotypes, the author’s findings where consistent with Browne-Cooper’s description of phenotypes. Although it seems to be the case with specimens from the western distribution, more so than those from the east.
Individuals from the western distribution most commonly present light cream or grey patterns that form irregular bands, these seemingly originate at the aforementioned lateral stripe displayed along the upper half of the body. Banding patterns are set against a dark base colour, although typically exhibiting shades of brown, base colours can also vary from grey, olive or black, to orange and even yellows. The base colour and lighter patterns are separated by a thin line of darker scales, giving a tri-colour look in much the same way that many other Carpet Python phenotypes do. A small handful of specimens exhibit darker patterns instead of the typical cream, when set against a dark base colour this can create a striking and unique appearance.
For the western distribution, habitat influences phenotype, particularly colours. In a book published by Mike Swan in 2007, Browne-Cooper described individuals of the western coastal region (within their range), as having contrasting colours, often with a tinge of yellow or lime. Whereas less vivid specimens are most often found at higher elevations, such as the darling ranges. The same is still true today, to the extent that for this project, locality specific populations where almost mapped as an alternative to the distributions. These locality maps would have been based on phenotype trends that significantly correlated with the Western Australian reptile keeping community. However, relying on phenotype trends would not account for the entire distribution, which is an error that the author believes to have been made with previously mapped subspecies for this project. Additionally, of locality populations mapped so far, (using greater cairns region as an example), most have been significantly impacted by the surrounding geography. Barriers such as mountain ranges, habitat types and large bodies of water, even land clearing and the development in housing and agricultural infrastructure has played a part in isolating populations. With Australia’s landscapes being so vastly diverse, the geographic situations that may have influenced phenotype consistencies within locality specific populations in some regions, have not had the same effect with other populations elsewhere.
While mapping Morelia imbricata has certainly shown that phenotype trends based on habitat type do exist, the present author was unable to confidentially isolate populations due to an adaptation not seen in any populations mapped so far. Unlike other population that remain restricted to specific habitat systems, Morelia imbricata has adapted to an impressively diverse range of habitats. From dense eucalypt forests, woodlands, high altitude habitats such as those found on the Darling ranges, to coastal cliffs, dunes, sandy plains, heathland, shrubland and rocky outcrops of limestone and granite, (Browne-Cooper, 2007). Morelia imbricata also appear to be becoming more urbanised, adapting to thrive in close proximity to each other, people and relying on our infrastructure to provide food, shelter and key resources in both rural and urban settings.
But is this reliance by choice, or a necessary adaptation in response to continued habitat destruction?
One extreme example of urbanisation in Morelia imbricata was discovered by homeowners in September of 2023, when they learnt that their newly bought property (which included a double story shed that has previously stood abandoned for 20 years), was occupied by well over a dozen South-western Carpet Pythons. Situated on 80 acres of property and surrounded almost entirely by crop fields, the shed has provided a safe haven for Morelia imbricata with enough prey in surrounding fields to support a large number of pythons and other snake species for the past two decades. And it continues to do so, the author was informed that the family is still happily living alongside their reptilian neighbours. Pythons receive complimentary tick removal, on site health checks, an abundance of prey from surrounding farms and in turn provide a natural pest control. A database has been created over the past year, using head patterns to ID individuals and track their movements around the property with minimal disruption to their daily lives and routines.
Despite this versatility in both habitat and cohabitation, and an increase in urbanisation, a number of studies found Morelia imbricata to be in decline across much of their range. In almost all cases, destruction of habitat in favour of agricultural land was primarily to blame, (smith, 1981)(bush, 1981)(Pearson, 1993)(Pearson et al, 2005).
A study on South-Western Carpet Pythons, conducted at both Dryandra and Garden Island found that individuals of this species exhibited high site fidelity. 91 pythons were tracked for as long as 4 years, those on the mainland often returned to the same hollows and logs, even after long absences. Many of these logs were felled during logging over half a century ago, with little effort made to regrow source trees, (Pearson et al, 2005). In the same paper, Pearson described the complications of bushfire, and its impact on pythons and their habitats. Low-intensity fires (like those used in controlled burns), reduce the availability of logs and ground cover while failing to regenerate shrub thickets used by both pythons and prey. Whereas high-intensity fires regenerate shrub thickets and create new logs with the trees that are felled during the burn. This process may destroy tree hollows, but high-intensity bushfires also have the potential to form new hollows faster than those formed over 200 years in undisturbed mature trees, (Wagner et al, 2024). An increase in controlled burns in WA since the 1950s (Burrows, McCaw, 2013) may have a delayed impact on the continued suitability of habitats within the WA distribution of Morelia imbricata. But stories like the one shared, are a reminder that we can live alongside our wildlife, and that doing so can be beneficial in preserving species like Morelia imbricata. Where a reduction in suitable habitats and an increase in urbanisation could mean their continued survival.
Acknowledgements:
Foremost I thank Phil Patterson, for his dedicated guidance, support and comments on this article. I am grateful to Chris Jolly and Brian Bush, for insightful information, advice and photos provided over the course of this mapping segment. Thanks to Jamie Dolphin, Tiarnah Kingaby, Forrest He, Amelia Lague and Glen Gaikorst for providing photos. I also thank members of the WA Naturalists’ Club and Western Australian H**petological Society for information, experiences and local knowledge that was kindly shared.
References:
Smith L.A. 1981. A Revision of the Python Genera Aspedites and Python (Serpentes: Biodae) in Western Australia. Records of the Western Australian Museum V.9 no.2: 211-226.
Webb J.A., James J.M. 2006. Karst Evolution of the Nullarbor Plain, Australia. Geological Society of America Special Paper 404: 65-78.
Alley N.F., Clarke J.D.A., Macphail M., Truswell E.M,. 1995. Sedimentary Innllings and Development of Major Tertiary Palaeodrainage Systems of South-Central Australia. Palaeoweathering, palaeosurfaces and related continental deposits: 337 – 366.
Esquerré, D. Donnellan, S. Brennan, I. G. Lemmon, A. R. Lemmon, E. M. Zaher, H. Grazziotin, F. G. Keogh, J. S. 2020. Polyogenomics, biogeography, and morphometrics reveal rapid phenotypic evolution in pythons after crossing Wallace’s line. Systematic Biology V.69 no.6: 1039-1051.
Chen, X. Y. Barton, C.E. 1991. Onset of aridity and dune-building in central Australia: sedimentological and magnetostratigraphic evidence from Lake Amadeus. Palaeogeography, palaeoclimatology, palaeoecology V.84: 55-73.
Short, A. D., Tamura, T., Oliver, T. S. N., Detmar, S., Fotheringham, D. 2024. Quaternary clifftop and glacial maximum dunes around the Great Australian Bight. Quaternary Science Reviews. V.327 no.108517
Clark, P. U., Mix, A. C. 2002. Ice sheets and sea level of the Last Glacial Maximum. Quaternary Science Reviews V.21 no.1-3: 1-7
Williams, A. N., Ulm, S., Sapienza, T., Lewis, S., Turney, C. S. M. 2018. Sea-Level Change and Demography during the Last Glacial Termination and Early Holocene Across the Australian Continent. Quarternary Science Reviews V.182: 144-154.
Browne-Cooper, R. 2007. South-western carpet python, Morelia spilota imbricata (Smith, 1981). In: Swan, M (Ed.), Keeping & Breeding Australian Pythons (pp. 261-275). Lilydale, Victoria, Australia: Mike Swan H**p. Books.
Bush, B. 1981. Reptiles of the Kalgoorlie-Esperance region. Brian Bush: Esperance, Western Australia.
Pearson, D. J. 1993. Distribution, status and conservation of pythons in Western Australia. H**petology in Australia: 383-396.
Pearson, D., Shine, R., Williams, A. 2005. Spatial ecology of a threatened python (Morelia spilota imbricata) and the effects of anthropogenic habitat change. Austral Ecology V.30: 261-274.
Wagner, B., Baker, J. P., Nitscke, R. C. 2024. How an unprecedented wildfire shaped tree hollow occurrence and abundance – implications for arboreal fauna. Fire Ecology V.30: 1-18
Burrows, N. McCaw, L. 2013. Prescribed burning in southwestern Australian forests. Front Ecol Environ V.11 no.1: 25-34
05/08/2025