- Last updated:
- 21 Oct 2019
Our lawn looks like a green moonscape. There are hundreds of little mounds, 5 - 7cm high, composed of grains of soil excavated from the substrate. Judging by comments and questions from other residents, the situation is widespread. They are the handiwork of the Pasture funnel ant (Aphaenogastor pythia).
These yellow-brown ants are very small, only about 4mm long. Unlike many other ants which have major and minor workers, all the workers of this species are of the same caste and of the same size (monomorphic). With a good lens the 12-segmented antennae with 4-segmented clubs are visible and can help distinguish these ants from other similar species.
Of course the prominent mounds themselves are distinguishing features. Every mound has one or more openings 5 – 10mm in diameter which act as a funnel in the roughly cone-shaped structure. The funnels are thought to act as traps for small arthropods and assist in drying out the nest. Some of our visitors from Europe were intrigued by the small size of what they thought were mole-hills and by the large number of them.
The scientific name “pythia” suggests that this ant was named after Pythia, a famous oracle (fortune teller) in ancient Greece. Locally, the belief is that when these ants make their mounds rain is imminent. Out in the desert we have noticed ants of different species building little “survival” turrets when rain was approaching. They were consistently accurate. At home here, we have observed that our Pasture funnel ants are equally accurate, not at forecasting rain but only at telling when it has rained recently. Not really much use – even the weather bureau can get that right.
There are about 200 species of Aphaenogaster world-wide. Australia has four species in that genus. Our species pythia is found in a narrow band up the East Coast of Australia in three widely separated populations, which indicates that they may in fact be closely related but different species.
Excavating the soil and bringing it to the surface like they do is known as bioturbation. It alters the structure of the soil and affects aeration, water- holding and permeability. Earthworms and other burrowing organisms, including plants, also work the soil. In marine environments bivalves and other filter- feeders play a part in arranging substrate structure.
Here on our lawn we do not regard the ants as a serious problem; they clog up the lawnmower blades but in return they aerate the lawn for us and at some stage they will go away. Of course hundreds or even thousands of mounds on the fairway of a golf course would certainly interfere with play and be a nightmare for the green-keeper. In fact these ants can affect the structure and consistency of the soil to a degree where they cause a hazard to aviation using unsealed runways. In some soils they interfere with the roots of crops including sugar cane.
We have inspected quite a number of the mounds and found very few ants on the surface. The main nest would be down at or below the root zone of the grass where the workers are known to tend, and extract nourishment from certain aphids and scale insects feeding on the grass roots.
Our lawn also harbours seemingly millions of the nasty Green-head ants, Rhytidoponera metallica. We wondered if there was conflict between the two species. Only one funnel-mound (of 40 inspected) had been taken over by the usually aggressive Green-head ants; the rest were still occupied by the funnel builders.
In areas where these ants must be controlled for commercial or safety reasons, professional pest controllers have a number of effective reagents. Repeat applications are usually required.
Aphaenogaster pythia appear to be non-aggressive – little information on defensive behaviour is available. We have given them ample opportunity but have never suffered a sting. We cannot say the same for the habitat-sharing Green-head ants.
Article by Kon Hepers