However, the basis for this cooperation between the two species was by no means secure. For a start, compared to the myriad hardships faced by the dinosaurs – hunger when prey was scarce, thirst when water sources had dried up, injuries sustained in fights with their own or other kinds of dinosaur, not to mention a host of fatal diseases – getting meat trapped between their teeth was a mere piddling inconvenience. Quite a few of the dinosaurs who sought out the ants for a teeth-clean did so out of curiosity or for a lark. Equally, once the dry season was over, food would become plentiful again for the ants, and they would no longer need to rely on this unorthodox method of sourcing their daily meat. Attending those terrible banquets in the dinosaurs’ mouths – so very like the gates of hell – was not something most of the ants relished.

It was the arrival of a Tarbosaurus with tooth decay that marked a major step forward in dinosaur–ant cooperation. That afternoon, nine dinosaurs had come to have their teeth cleaned, but this particular Tarbosaurus still seemed restless even after its procedure had been completed; one might even describe its mood as antsy. It held its forearm high to prevent the cleanser ants from leaving and with its other claw gestured insistently at its teeth.

The mayor in charge of that colony led a few dozen ants back into the Tarbosaurus’s mouth and examined the row of teeth carefully. They quickly discovered several cavities in the smooth enamel walls, each large enough to admit two or three ants side by side. In went the mayor, braving one of the cavities, and several other ants crawled in after it. They scrutinised the walls of the wide passageway. The dinosaur’s teeth were very hard, and anything that could tunnel through material as tough as that was indisputably a digger to rival the ants themselves.

As the ants felt their way forward, a black worm twice their size suddenly erupted from a branch passage, brandishing a fearsome pair of razor-sharp mandibles. With a click, it bit off the mayor’s head. A bundle of other worms then burst out of nowhere, divided the column of ants in the tunnel and launched a ferocious attack against them. The ants were too exhausted to defend themselves and in an instant more than half were slaughtered. Those that did manage to break through the encirclement raced past the black worms but quickly became disoriented in the labyrinthine passages.