Y’see, ant society is kind of like a miniature version of The Outsiders. It’s the ants on one side, and all the forces of nature that want them dead (humans included) on the other. Each member of any ant colony really only has two goals:
1. Try to stay not dead
2. While not dead, spend time alive gathering food and trying to make predators dead.
Because most all ants have this rather short bucket list preprogrammed into their tiny insect brains, they’re always killing each other and fighting against bigger predators (in the carpenter ants’ case, larger insects and spiders). Picture hundreds of Civil Wars and War of the Worlds going on right inside your backyard, complete with little Battles of Gettysburg.
This is where autothysis comes in. Apparently, this tactic is only ever used as a weapon of last resort. Think of it as a one-insect banzai charge. Carpenter ant soldiers have a network of huge glands running from their mandibles to their abdomens, and each gland is surrounded by a ring of muscles. The glands contain a special adhesive solution, a kind of glue (hereafter known as bio-glue). When the going gets tough and the ants are about to lose, they contract those mandibular gland muscles and let loose their bio-glue. This epic defense, as the title suggests, blows their freaking heads apart in the process. It also leaves behind a sticky mess of dismembered ant parts, bio-glue, and the now-trapped predator that will require therapy for the rest of its short insect life.
The soldier ant doesn’t kill itself in vain, however. Aside from being a chemical irritant, the glue also contains some kind of signaling pheromone, telling the other ants to swarm around and finish off the now-trapped enemy. Hopefully it involves the ants chaining their head-bursting powers together to create an ant-sized thermo-nuclear explosion.