INTRODUCTION / SUB FAMILY / GENUS

Spiny ants belong to the Formicinae sub-family and the Polyrhachis genus. They are the far away cousins of our worldwide beloved Carpenter Ants (e.g. Camponotus nicobarensis, Camponotus lianghuang).

Polyrhachis is a genus of formicine ants found in the Old World with over 600 species. The genus is yet to be fully understood and described because it is one of the most ecologically diverse ant genera in the world. It contains so many varied species which span so many different types of habitats including mangrove, soil and tree-dwellers.

They can be easily be identified due to the big spikes most workers showcase as a defensive mechanism against predators.

DISTRIBUTION

This ant genus is exclusive to the Old World (Africa, Asia and Oceania).

COMMON NAME

Polyrhachis - from the Greek words : Poly + Rhachis.

The prefix poly- means “many” and the suffix -rhákhis (ῥάχις) means “spine or ridge”. In conclusion, “the spiny ant”

MORPHOLOGY

The general morphology of Polyrhachis workers range in size approximately from 5-10mm in length.

Mesosoma, or thorax, of most species have spines on one or more of its pronotal, mesonotal or propodeal components. Petiole armed with spines.

Polyrhachis dives worker foraging for water droplets on the leaves surface.

Of course not all the species showcase the same amount or similar sized spines. Some only have small bumps instead of spikes.

Polyrhachis moesta worker foraging. Notice the lack of noticeable spikes.

It is speculated that the spiny ants spikes, serve as a deterrent against predation. And that those species who employ larger spines are found more often foraging, being more conspicuous, which means, they are less afraid of being eaten and so, can spend more time foraging and gathering resources for their colony. I would recommend you read the following research paper regarding this matter.

Spine and dine: A key defensive trait promotes ecological success in spiny ants

“…We investigate potential benefits and costs of a common and varied morphological trait, cuticular spines, for foraging behavior, interspecific competition, and predator–prey interactions in naturally co‐occurring spiny ants…”

Being such a diverse ant genus, you can find Polyrhachis workers foraging on any type of habitat and at any given height…. from the undergrowth, to the tree level, up to the top of the canopy, Polyrhachis can be found anywhere at any hour of the day. Of course, like most ants, night foraging feels always safer.

FORAGING

Polyrhachis do not have a stinger but an acidipore that can spray formic acid. When attacking, this is often sprayed in combination with biting thus making the acid more effective against the subject of the attack.

Just like their Camponotus (or Carpenter Ants) cousins, Polyrhachis (or Spiny Ants) have a varied diet. Their food resources vary from:

1 - Trophobionts - Homopterans like aphids and others, which they attend to in order to collect their honeydew secretions.

2 - Plant and shrubs nectaries - Plants can also produce and secrete sugary substances in order to attract ants to forage on them. While foraging, if any worker ant comes across a potential prey item, it will quickly mobilize its colony companions to seize and capture it, removing this potential danger to the host plant.

3 - Dead and living insects - Most Polyrhachis will have a preference for dead insects instead live ones.

NESTING

Polyrhachis species include an array of nesting types ranging from terrestrial, soil based nests to arboreal nests. As a result, the nest architectures also vary with some species displaying a high level of complexity to nest building, utilizing larval silk to weave nest materials together.

According to Bolton (1973) - The nesting habits of the genus as a whole have been discussed by Hung (1967) who sums up by saying that four types may be recognized, as follows:

1. Arboreal: carton and silk nests amongst leaves and twigs.

2. Lignicolous: nests in the cavities of plants.

3. Terrestrial: nests on the ground under any object.

4. Subterranean: nests in the soil, without cover.

Nesting and food resources in the ant genus Polyrhachis

And now this is when the genus starts to become complicated to define and understand. Polyrhachis genus is sub-divided into multiple sub-genus groups, each one with its own characteristics. For the new ant keeper, research and further study is a must to be able to successfully keep this species.

Being so diverse, one wouldn’t want to keep a subterranean Polyrhachis in an arboreal setup and vice versa.

ECOLOGY

Based on a review of 197 of the approximately 600 described species of Polyrhachis, the majority of species within a particular subgenus demonstrate a consistent ecological type but a few species can be highly variable, demonstrating both subterranean and arboreal habits.

I would recommend you read the following research paper regarding this matter.
Nesting and food resources of syntopic species of the ant genus Polyrhachis (Hymenoptera, Formicidae) in West-Malaysia

”…We investigated the nesting and nutrition habits of 10 … species of Polyrhachis in … striking differences between these species exist in regard to their habits…”

REPRODUCTIVE STRATEGY

Polyrhachis seem to incorporate (once again) multiple reproductive strategies within the same genus, only varying from species to species.

Some species are monogynous while others are polygynous. Some species are capable of pleometrosis (pleometrosis is a behavior observed in ants where colony formation is initiated by multiple queens). Some species are social parasites such as Polyrachis lemalidens, where usually Camponotus japonicus is the host.

Within the polygynous species, the colony structure also varies, where the numbers of nests and queens per colony can differ for each species.

In this case, either by in loco observation, by researching, experience and experimentation or networking with other ant keepers, will one be able to identify and know which will be each species reproductive strategy.

WHY DOES THIS MATTER?

Well, because I got three new Polyrhachis species in my collection. Well to be honest not new, but I am giving them another try.

But first let me bring up the Polyrhachis sub-genus list in which my species are included.

Aulacomyrma Emery, 1921
Campomyrma Wheeler, W.M., 1911
Chariomyrma Forel, 1915
Cyrtomyrma Forel, 1915
Hagiomyrma Wheeler, W.M., 1911
Hedomyrma Forel, 1915
Hemioptica Roger, 1862
Hirtomyrma Kohout, 2010
Myrma Billberg, 1820 - Polyrhachis illaudata
Myrmatopa Forel, 1915
Myrmhopla Forel, 1915 - Polyrhachis armata
Myrmothrinax Forel, 1915 - Polyrhachis thrinax
Polyrhachis Smith, F., 1857

The first one, Polyrhachis armata, one of my favorite looking Polyrhachis species. The jet black with the heavily bodied armor and the heavy spikes, omg!!

I got five queens, which I decided to leave all together, and one has already died (shortly after arriving), so I am down with four queens. But they seem to be doing great, they have many eggs now! Let me show you some of my older photos and attempts to keep this species before.

Polyrhachis armata queen foraging

This species is a carton nest weaver. If you scroll back up, you can refer to the nests type E and F . Also these photos below are not mine, but they will give you an idea of how some of the nest would look like in the wild.

This was also a big revelation for me, as it shows a new leaf silk with debris. A sort of a compromise solution, between a fully weaved green leaf nest like those from Oecophylla smaragdina and a fully cartoned nest like those from Polyrhachis dives, which I showed before.

The first and only time I was able to find this species in the wild was back in 2018 during a working trip to Singapore. On my last day, I went to MacRitchie Reservoir, and spent the whole afternoon there photographing ants and whatever I could. I still remember my excitement when I spotted these workers!

Their gasters have a slightly reddish tone to it, unlike my queens, which are totally black. I don’t know if its a sub-species or if I am actually getting a wrong id here…

Now moving onto another favorite of mine…. a small red species. In Chinese they are known as the Blood Red Polyrhachis (血紅多刺蟻) Polyrhachis thrinax !! Unfortunately I don’t have any macro photos of them yet… i am sorry! So I have to post some older photos for you :(

My actual colony does look a lot like this one on the photo above! With 1 Queen with workers with similar colony size and worker coloration distribution.

This species is also a small arboreal species, which does cartoon nests utilizing dead leaves and other forest floor debris.

Polyrhachis thrinax queen with a webbed entrance barrier to protect her.

And finally a local Macau species, which I have never been able to raise successfully from queen. Polyrhachis illaudata!

I have managed to capture two queens and I placed them together as soon as I got back home. There was no signs of conflict and after a quick bash of antennae, both queens seemed to have recognized each other. Maybe they were from the same original nest.

This species can be really finicky… I have kept queens before but without any warning they just die off. This is the first time I have actually got so many eggs and a great initial response from them after capture.

If I recall correctly not even 2 days after getting them, they already had layed 1 egg or 2.

CONCLUSION

All the species above, I am keeping as semi-claustral species, which they clearly are. Always providing water and honey water separately in their small and closed outworld. At this moment, P.armata and P.illaudata have not yet been fed any insects, and I will only do that once larvae appear.

As for the P.thrinax, same principle, just the exception of the occasional freshly crushed baby red runner roach, which they love.

Hope you have enjoyed reading this post and I have left you a small video in the link down below with each of the colonies, in case you are interested.

Thank you once again for stopping by and taking the time to read.

Bye! Cheers!

Here is a new YouTube unexpected video!

And I also leave you, one of my older video about Spiny Ant Queens, I caught in Macau, and my attempts to raise colonies.

An older YouTube Video about Spiny Ants in Macau

Polyrhachis - The Spiny Ants