The only species in the genus Cosmobunus, this is a fairly large harvestman, with a body about seven millimeters long in males and nine in females, and a leg span of about six centimeters. Its body is globose and dorsally adorned by a wide longitudinal straw-colored band, bordered on its sides by almost black bands that gradually fade toward the grayish-brown exterior. However, its coloration is highly variable; in the lighter specimens, the central light band has only a few dark spots delimiting its sides, while in the darker specimens, the two dark bands bordering the central one occupy almost the entire abdomen. The protuberance where the eyes are located (ocular tubercle) is light yellow and has two black eyes, surrounded by a circle of six teeth. The pedipalps, chelicerae, and coxae are pale creamy, while the legs are brownish, darkening at the joints. The legs are very long in proportion to their body.
It is distributed throughout the eastern and southern Iberian Peninsula, southern France (where it was not discovered until 2017), and North Africa, having been initially described from Algeria. It is nocturnal and remains hidden in shady places during the day. Juveniles are always found on the ground, but adults, on the other hand, move through herbaceous or shrubby vegetation or tree trunks. It feeds on dead organic matter, both plant and animal, especially fallen fruit and dead insects. Perhaps the most striking aspect of this species' behavior is its tendency to congregate in dark places such as the ceilings and walls of tunnels, mines, and caves (but never far from the entrance) or under bridges, where it often forms very compact masses with countless individuals, sometimes more than a hundred.
Due to the great length of their legs, their bodies remain hidden in this mass, and the forest of legs resembles a strange growth of fungi or fine rootlets hanging from the cave walls. When individuals have not found one of these masses to congregate around and are forced to rest alone, they do so with their bodies wedged into a crevice and their legs pressed as far against the substrate as possible, making them much more difficult to detect both visually and by other means (such as bat radar). Despite its strong association with caves and similar roosts, the species is also capable of living outdoors, where females bury their eggs in the ground in autumn, hatching in early spring. The young transform into adults in early summer, and after reproducing and laying eggs again, they die in autumn. In caves where environmental conditions are stable year-round, however, the species reproduces year-round and its adult lifespan is prolonged.
