What has constructed the small mudbrick “chimney” shown in the photo? Ants? Some other insect?
The answer is a land yabbie, more correctly known as a land crayfish.
The land yabbie is a small yabbie-like creature with a smaller tail section than the common yabbie. There are several species, most of which are no more than 45mm in body size.
This photo, supplied by a reader, was taken a few months ago on the rail trail at Wombat, on the edge of the forest, south of Daylesford.
There is no supporting base to the “chimney”, and the pellets appear to become more separated as the tower extends. This could be related to the yabbie burrowing into drier clay.
The land yabbie lives in a wet hole at the bottom of the tunnel, feeding on rotting vegetation and similar matter. Some species live colonially.
There are usually several entrances to their underground watery caverns, in which they spend their entire lives. Most of their activity is at night. The water table is followed down – sometimes for two or three metres – as summer and dry weather proceeds.
When burrowing, they bring pellets of soil to the surface and place them around the entrance, resulting in the distinctive “chimneys”, but the purpose of these is not known.
Most land yabbies occur in eastern rather than western Victoria. Some species are rare and threatened. Their burrowing and their muddy entrance holes make them unpopular with many landowners, especially when they disfigure lawns. Their occurrence and status in the Ballarat region seems to be rather unclear. They are normally found in damp muddy places, rather than the dry site pictured.
How much taller can these neat little towers be made? The one shown is 40-50mm tall, but appears to be rather fragile, so it is probably near to its maximum height. However, towers up to 40cm have been reported elsewhere. Pelletised towers are rather uncommon – mostly they are made from wetter mud, resulting in a shorter, bulkier, less distinct and less eye-catching structure. There are similar chimneys made by ants, but they are shorter and wider, with a tapered supporting base. The pellets are much smaller.
Common heath – Victoria’s floral emblem – is unusual for its wide range of colours, ranging from white through to red.
It is currently flowering nicely in several spots, notably Linton, Incoll’s Road at Enfield, and bushland around Bungal Dam. There are also attractive sprinklings at Canadian Regional Park.