Peter - To identify these you would need an actual ant (easy enough to get, I would think) and a low-power microscope, my own researches becoming lost in the myriad of possibilities. Lindell kindly referred me to a Queensland website with a picture of a rather similar ‘Rattle Ant’ or ‘Dome-backed Spiny Ant’, but Elizabeth’s ants do not have the obvious dome of the thorax, but rather a flattish shield. There is an interesting website, ‘Antwiki’, which offers among other things a ‘Key to Australian Genera of Formicinae’ . This is where your dead ant and microscope would be needed. My own photos were not aimed at any particular part of the ant, and it is to a very specific part or parts that your investigation must be directed. The first step in applying the key involves counting the segments of the antennae. It is critical whether there are ’10 or 11 segments (including the scape)’ or ‘12 segments (including the scape)’. Now consider the below photographs. I am of the clear opinion there are 11 or 12 segments. At a stretch, the segments are countable, but one quickly runs into the difficulty of the ‘scape’. This might be something that an entomologist thinks is within the comprehension of any fool, but I am reluctant to start hunting for a glossary that will be needed more than once in the application of the key.
The all-important ‘scape’ comes up more than once in your journey through the key, including whether it has hairs. To cut this short, my own suspicion is that the subject ants are members of one of the following genera: Polyrhachis, Oecophylla, or Camponotus, the final diagnosis depending largely on the number of teeth on the mandible, and whether, for example, the fourth tooth is longer than the third and fifth teeth. Without going into the potential impact of these species in the home garden (or home) I will just mention that Camponotus is also known as the Carpenter Ant and can, allegedly, cause structural damage in timber work.
From: Peter Ormay [
Sent: Wednesday, 28 May 2014 9:53 AM
To: 'Geoffrey Dabb';
Subject: RE: [canberrabirds] ACT Fat-bummed Cactus Ant
I suggest they be positively identified in case they are an introduced species and could become a pest.
This afternoon, Elizabeth Compston of Wells Gardens, valued member of this chatline and tireless advocate of name-tag wearing, asked me to photograph some unusual small ants she had discovered in her cactus garden. The ants appeared to have made a coffee-cup-size nest of fine plant material, matted together, at the base of a cactus plant, They were about 3mm long excluding antennae. Most (not all) had an unusually large abdomen by comparison with the normal run of picnic ant. I said to Elizabeth: “Someone is bound to know about these chaps” … (?)