Post image for Mulga ant nest

Mulga ant nest

July 30, 2009

in Australia

The distinctive nest of the Mulga ant, Polyrhachis macropus. These nocturnal ants live in central Australia, scavenging for seeds, fruits and dead insects and excavating nests that send tunnels up to a metre long into the hard-packed red earth. They surround the entrance with a ring of mulga phyllodes (part of the stem that acts as leaves) that can be as big as 15cm high and 50cm across.

Why they build these rings is a mystery. One theory is that because the soil of the red centre doesn’t absorb water easily, the ring acts as a miniature levee to protect the nest from flooding during the infrequent rains. Another theory is that the rings help to cultivate a fungus which the ants either eat or drink from – evaporated moisture from soil or dewfall could be collected by the fungus.

The neat circular nests are a pleasing sign of order in the vast wild landscape. This small one caught my eye because of the clump of dead grass next to it. It was like a diagram of a comet and a nebula drawn on the desert soil. And I can’t blame the heat for my flight of fancy as it was still early morning.


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