reiasai97's Identifications

Alright let's take a look at this. It's distinctive so hopefully we can get a name. Hopefully. There are a few other sightings of what may well be the same species too (the first one almost certainly is). There are 78 species of Rhytidoponera listed for Australia and I will not be detailing the specifics of ruling them out because there are so damn many. So I'm pretty much just gonna go through and rule out the obvious ones, and then go through again and look for more subtle things.

So going through all of them, we reach a shortlist of about 30 that could conceivably be found here. Ruling out those with obvious 'horns' at the back of the head brings us down to 25. R. fuliginosa and R. greavesi have no face images available but from the other images they certainly seem to have horns so I will treat them as such. R. metallica and R. purpurea are species I know well, and I can rule them out easily based on colour.

Okay, so 23 species - that's pretty doable. What features can we look for though? Well aside from the different colour of the gaster, it's also very noticeably shiny compared to the rest of the body, which is quite sculptured. There are a few species with significant sculpturing on the gaster which we can rule out - R. chnoopyx, R. inornata, R. kurandensis, R. maledicta, and R. scaberrima. In addition, the scapes of the antennae exceed the back of the head by a significant margin, so we can rule out R. anceps and R. victoriae.

Alright, down to 16 which is very reasonable. What else can we rule out though? Well the petiole is at least moderately thick, so we can rule out R. lamellinodis and R. turneri. The sculpturing is pretty much exactly the same between the head and the mesosoma and does not include obvious thoracic striations, so I think we can rule out R. impressa, R. laticeps, R. scabra, and R. socrus. And additionally, the sculpturation consists of moderate punctures that are at least large and dense enough to be easily seen, so we can rule out R. cristata and R. yorkensis.

Halved down to 8, but now it gets tricky. The frontal carinae are definitely quite diagonal where they cover then antennal sockets, so we can rule out R. tenuis at least. R. reticulata has the carinae a little more diagonal but still not enough, and there is not really significant variation in this in the four specimens pictured on AntWiki so I am happy to rule it out as well. The hind margin of the head is at least a bit concave, so I think we can safely rule out R. rufescens and R. spoliata as well.

Four to go, and now we are struggling :P Okay, well let's get a general feel for what is likely from the options. Colour and range aren't definitive things, but they are useful for working out what is more or less likely. R. castanea is a variable species (in colour at least) that has not been recorded particularly close to here - the closest record is in Coen. Some individuals are bicoloured, but in those ones the gaster is darker than the mesosoma rather than the other way around as we see here. R. convexa is a rather more unicolourous species, but it has been recorded several times very close to here. R. mayri is also mostly unicolorous, but some individuals have a slightly paler abdomen. The vast majority of records are very far from here, in inland NSW, SA, and WA, although there is apparently a single record from near Cooktown. I'm not really sure on the validity of that record but it's impossible to say. And finally, R. rufiventris is a unicolourous to bicoloured species, with the gaster sometimes much paler than the mesosoma. It has a few scattered records across northern WA, NT, and QLD, with a cluster of records from near here. So obviously from this, R. rufiventris is by far the best option, and it is indeed also the species suggested by my ant expert @reiasai97.

But it would still be good to definitively rule the others out based on some structural grounds, if I can. R. mayri seems to have obvious radiating carinae on the occiput, which are just not visible in my specimens. Even with my poor photos I would expect to see them, so I am happy ruling it out. What about eye size? In R. castanea, the head is about 4.48 times the length of the eye, in R. convexa it is about 5.08 times the length of the eye, and in R. rufiventris it is about 5.63 times the length of the eye. That's very helpful! In mine, the head is about 5.65 times the length of the eye. So that is pretty convincingly R. rufiventris! The colour and distribution also match very well as we have seen. Thanks Rei! :P