Millipedes are surprisingly particular about maintaining their own territories. Robert Mesibov of Queen Victoria Museum and Art Gallery discovered that two species of Tasmanian millipedes, Tasmaniosoma compitale and Tasmaniosoma hickmanorum, maintain a border that is about 230 kilometers long. At places, the no-millipede’s land between the two regions is only about 100 meters across.
Caption: These are Tasmaniosoma hickmanorum and Tasmaniosoma compitale, preserved in alchohol.
Credit: Bob Mesibov.
It’s not uncommon for two similar species to maintain non-overlapping territories. However, this practice, known as parapatry, usually involves insurmountable physical barriers. For example, two species may live on opposite sides of a river or cliff face. In contrast, T. compitale and T. hickmanorum don’t appear to have any physical reason for their enforced separation.
Although 100 meters is pretty wide for a creature that’s only a few centimeters long, it’s narrow compared to the size of the entire territory. With no environmental impediments separating the two species, you’d expect them to intermingle. Even Mesibov is not sure why they don’t, as you can see from the report below.