High in the rainforest canopy of Borneo lives an ant that explodes as a defense mechanism. They're basically the original suicide bombers, blowing themselves up so they can take their enemies with them. The phenomenon has been known to science since 1916, and presumably to native peoples for a long time beforehand, but hasn't been studied as much as you'd expect – perhaps because scientists too can be targeted. Now the most detailed study of the culprits has been published, revealing a previously unknown species.
Ants are certainly not the only animals that engage in self-sacrifice for the interests of their colony. Honeybees are the most famous example of animals that will die to ensure the genes of their siblings are passed on. Nevertheless, Colobopsis ants are so extreme in their mechanism they have attracted a certain fame.
The ants explode by rupturing their internal walls, splattering enemies with a toxic goo. If it doesn't kill the threat or deter it from venturing closer to the nest, an individual ant's sacrifice might at least give the rest of the colony time to regroup.
Colobopsis ants are restricted to Southeast Asian rainforests, where they nest in dipterocarp trees, limiting research opportunities for many scientists. No new species had been described since 1935, until an international team decided to rectify the situation.
The researchers have described a new species, Colobopsis explodens, in Zookeys. Besides the excellent name, the paper proposes C. explodens as the model species for research into the exploding ant phenomenon, although it also describes others who engage in similar behavior.
Apparently, while multiple Colobopsis ants can explode, some are more inclined to do so than others. The authors called C. explodens “particularly prone to self-sacrifice when threatened by enemy arthropods, as well as intruding researchers" in a statement. Its emissions are also a bright yellow color distinctive to this species and have an unusual spice-like smell.
A colony will have multiple nests and thousands of ants, with a strict caste system. Explosions are a feature only of the “minor workers”, suggesting the colonies might be ripe for a socialist education program questioning why it is those at the bottom of the hierarchy who are expected to sacrifice themselves for the more privileged.
Major workers have larger heads than minor workers, which they use to block nest entrances so invaders cannot enter, rather than exploding outside.
Like other ants, Colobopsis have queens and consort mates, but these had never been seen until the study authors, Alice Laciny of the Vienna National History Museum and Vienna University of Technology's Dr Alexey Kopchinskiy, witnessed a mating flight in 2015 while gathering samples.