There is an African ant species of tiny workers that lives in big trees. In these big trees, the little ants scurry around long, narrow cavities in the bark, tending to the even littler insects they harvest as livestock. Outside of these big trees, the little ants can barely stand.
The difficulty that the gals have in standing up straight is owing to the unusual, upturned shape of their mid-coxa, the first segment of their middle legs. This morphology forces their middle legs into an upturned position, increasing grip in the bark tunnels they inhabit but hindering movement when outside the tunnels. Furthermore, as AntBlog Myrmecos noted in 2012, Melissotarsus ants may be the only non-humans known to farm animals for meat, and the adult workers spin silk!
Melissotarsus may have a mere four species to its name, but they’re four wacky species indeed.