A spiny black ant patrolling a tree trunk
This ant was patrolling a tree trunk in Lombok, surrounded by dense green foliage and fallen leaves, moving with the steady, purposeful gait that ants do so well. It was a long, slender ant, jet black, with long antennae and six legs that carried it easily across the bark. Most people would walk straight past it. I stopped, because this one was doing something interesting.
This is Polyrhachis armata, the armed spiny ant, a member of the family Formicidae in the order Hymenoptera. The species name armata means armed, and it fits: the thorax is covered in sharp spines, giving these ants a genuinely prickly look. Polyrhachis is a huge genus of spiny ants found across the Old World tropics, and many species are famous for weaving nests from silk produced by their own larvae, stitching leaves together into shelters.
Spines on ants serve a simple purpose: they make the ant harder to swallow. A bird that grabs a Polyrhachis quickly learns that the mouthful comes with hooks. The species is widespread in tropical Asia, and in Lombok it seemed to be everywhere on the lower trunks, a common sight once you start looking. Watching one up close, you notice how carefully it moves, pausing to sweep its antennae over the bark before taking each step, reading the surface for trails and threats.
The name armata always makes me smile, because it sounds like the ant read the instruction manual on defence and followed it literally. Spines, speed, silk nests and teamwork, this ant is armed in every sense of the word.
