Floored by Ant Mounds: Identifying ‘Ant Bed’ Floors in Buildings at the Boralga NMP Camp using GPR

By Kelsey Lowe

Making a floor out of earth (or ‘dirt’) is one of the quickest ways of creating a surface to live on and was a common type of flooring in the earliest buildings in Australia. An earth floor doesn’t require any special or costly resources, could be made by anyone without any special skills, and was surprisingly hard-wearing. The simplest floors were just trampled by human feet, and needed to be watered regularly to stay firm and keep down the dust (Edey 1981; Freeland 1968:13; Lewis 2014; Sorensen 1911). The best earth floors, however, were made from a material that is common across much of Australia: crushed ant or termite mounds (Figure 1).

Figure 1 Images showing use of ant bed mounds (left to right): floor (Old Laura homestead) and tennis court, as well as an ant mound and ants.

Not all ants live in mounds, but those that do send thousands of workers out to collect tiny mouthfuls of dirt that they then cement together with their saliva to make large and complex mounds to protect the nest. When crushed and mixed with water this material makes an excellent floor—it’s very fine and the ants’ saliva helps bind the particles together. Historically, kitchens, tennis courts, cricket pitches, dairies and smithies all commonly had floors made from ant-bed since all of these surfaces were used a lot and so had to be very hard wearing (“Eureka” 1935:10). Incidentally, because of their firmness and good insulation qualities, the mounds themselves also made excellent baking ovens, fireplaces and even ice-chests (Queenslander, 23 February 1938, p2). Because ant and termite mounds are found throughout Australia, buildings with ant-bed floors were common across the country, but especially in the north.

Many of the Native Mounted Police (NMP) camps we are investigating were temporary—some lasting only a couple of years—meaning that the buildings at them were usually very basic. Often they consisted only of canvas tents or open-sided shelters and even the longer-term camps typically only had very rudimentary timber and iron structures, roofed and walled with locally available material such as bark or grass. The advantages of this were that (1) they were cheap for the Qld Government to build, and (2) they could be easily dismantled when the order was given to shift camp. Given this, we assumed that many buildings at NMP camps probably had only simple earth floors rather than more elaborate timber flooring or flagstones.

The NMP camp at Boralga (also known as ‘Lower Laura’) sits on the floodplain of the Laura River, in the southern part of Rinyirru National Park about 18 km downstream from the town of Laura on the Cape York Peninsula (Figure 2). It was established by 1876 close to several critical resources: the Laura Telegraph Station, the Laura River crossing, and the Palmerville Track to the Palmer Goldfields (see Stephens 1972). The Boralga NMP camp operated until 1894, when it was closed and the buildings dismantled and their materials taken away for reuse (Cole 2004; Cole et al. 2002). The only historical plan of the site is Sub-Inspector Stanhope O’Connor’s 1877 ‘Plan of Police Reserve on the Laura River’, which shows a series of buildings between the lagoon and the river (Figure 3). According to an 1894 report there were seven buildings when the camp closed: 1) the officer’s quarters; 2) the constable’s quarters; 3) an office; 4) a store; 5) a saddle and forage room; 6) a forge and cart shed; and 7) the “trackers’” (i.e. troopers’) quarters.

Figure 2 Location map of the Boralga NMP camp and surrounding area (courtesy of Alyssa Madden).
Figure 3 Sub-Inspector Stanhope O’Connor’s 1877 ‘Plan of Police Reserve on the Laura River,’ which shows the entire camp area (238.5 acres) including six large buildings, the Boralga swamp (also referred to as the lagoon) and the Laura River (QSA A/44857).

In 1972 Jerry Musgrave, then a highly skilled Police Tracker at Laura with strong traditional connections to the area, guided Ernie Stephens of the Cairns Historical Society to Boralga. Here they found ‘old yard posts to take rails. Beyond were the old posts and ant bed floors’ (Stephens 1972:1). In a 2002 community archaeology project, Dr George Musgrave, who succeeded his elder brother Jerry as the Police Tracker at Laura, also identified a raised flat area near the Boralga lagoon as the remains of an ant bed floor that was likely from one of the tracker’s huts (Cole et al. 2002:142). Like Jerry Musgrave, Dr George Musgrave was a master tracker known for his remarkable ability to read the ground (Cole et al. 2002).

In 2016, when we did archaeological fieldwork at Boralga, we were interested in relocating these floors to help us work out where to dig. Luckily for the 2002 project there had been a controlled burn before their fieldwork, so archaeological traces on the ground were easy to see. In 2016, however, we had no such luck and there was a lot of grass covering parts of the site. To solve the visibility problem we used geophysical techniques, particularly GPR and magnetic radiometry  to help relocate the floors identified in 2002, and to potentially find more of these features.

The GPR data we collected in 2016 as seen in Figure 4 showed some very clear, rectangular-shaped and high amplitude reflections in different parts of the site associated with many of the wooden posts. Their size, shape, intensity and location suggested that these were likely compacted floors from at least four buildings. The figure below shows the processed data and amplitude “slice-maps” (measuring between 5-30 cm below the surface) for the floors of five different buildings (Figure 4b). These were described in the 2002 study as the officer’s quarters (Floor 1), the forge and cart shed (Floor 3) and the forge (Floor 4). We also found at least one unidentified floor (Floor 6) and one other possible floor (Floor 8). The reflections of these floors in our GPR data look very similar to known earth floors from other GPR studies (e.g. Conyers 2012).

Figure 4 GPR slice-maps of all geophysical survey areas (GSA) at Boralga sliced from 5–30 cm. (4a) Areas with higher reflections denoted by yellow and red. Figure 4b shows several anomalies, including the floors and ant mounds. Figure 4c shows a gradiometer map with black representing a positive magnetic gradient and white a negative gradient without highlighted geophysical anomalies. Figure 4d shows many positive anomalies, including floor and the three excavated dumps.

To understand how these floors were constructed and whether or not they really were made from ant bed, we also collected soil from elsewhere in the site, and from nearby ant mounds and analysed it in a lab. We measured the size of the soil particles, and worked out how much organic (plant-based) material was present in them using a techniques called ‘loss on ignition’ (LOI). We also measured how magnetic the samples were.

What we found was interesting. The soils in the area are mostly alluvial, which means they tend to have a high clay content, are usually grey in colour and stay saturated with water for long periods of time. The floors identified with the GPR and then excavated, and the natural soil samples we collected all had high amounts of sand in them and very low levels of silt (Figure 5). This means that all the soil sampled is local and that this natural material was combined into the humanly made features such as the floors. The natural soil samples also typically contained more organic matter and calcium carbonate than either the ant mounds or the floors. This is because natural soils have plants growing on them and plant growth increases both the organic matter and calcium carbonate in the soils. Ant bed floors were also watered regularly, so most organics or carbonates would have been removed over time by the water passing down through the floor.

Figure 5 Pie graph showing a positive correlation between the Boralga floors and ant bed mounds.

When we excavated the floors we found they were very hard to dig—so hard that we sometimes needed to use a small hand mattock just to break the surface. All of these traits suggest that the floors we found at Boralga were made from ant mound material. Buildings like the forge and cart shed would have needed hard-wearing and durable surfaces, especially in the wet season, but even the troopers’ huts—typically the buildings in which the NMP invested the least effort and cost—had such floors, the same as the officers. These floors, and the buildings they serviced, would have been built by the troopers and officers, as so many NMP camps were. Images of the troopers’ huts at Boralga show a neat row of bark and bush timber huts beside the lagoon (Figure 6).

Using geophysical techniques to identify the location of such features is one thing, but testing them through excavation and later laboratory analysis helps us to make better sense of them.

Figure 6 Troopers huts at the Boralga NMP camp ca 1870 (John Oxley Library collection Neg No 57330).


Cole, N. 2004 Battle Camp to Boralga: a local study of colonial war on Cape York Peninsula, 1873–1894. Aboriginal History 28:156–189.

Cole, N., G. Musgrave and L. George 2002 Community archaeology at Laura, Cape York Peninsula. In S. Ulm, C. Westcott, J. Reid, A. Ross, I. Lilley, J. Prangnell and L. Kirkwood (eds), Barriers, Borders, Boundaries: Proceedings of the 2001 Australian Archaeological Association Annual Conference, pp.137–150. Tempus 7. St Lucia: Anthropology Museum, University of Queensland.

Conyers, L.B. 2012 Interpreting Ground-Penetrating Radar for Archaeology. Walnut Creek: Left Coast Press.

“Eureka” 1935 Uses for ant-beds. The Argus 26 October, p10.

Freeland, J.M. 1968 Architecture in Australia – A History. Melbourne: Penguin Books Australia.

Lewis, M. 2014 3.06 Earth and composite floors.

Sorensen, E.S. 1911 Life in the Australian Backblocks. London: Whitcombe and Tombs.

Stephens, S.E. 1972 The Palmer Road in 1972. Cairns Historical Society Bulletin 337.

Richards, J. 2008. The Secret War: A True History of Queensland’s Native Police. St Lucia: University of Queensland Press.


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