Glomerida

Glomerida is an order of millipedes (class Diplopoda) commonly known as pill millipedes because of their ability to enroll into a nearly perfect ball when disturbed. Along with the related order Sphaerotheriida, Glomerida represents the pill-forming lineage of millipedes, but they differ in aspects of segmentation and exoskeletal organization.

Members have a compact, dome-shaped body formed by broad, heavily sculptured segments. Each apparent segment bears two pairs of legs, but the rings are wide and strongly fused, giving the animal a smooth, contoured surface. The first segment behind the head, the collum, is often shield-like, and the last segments contribute to a rounded posterior. Many species have reduced or absent eyes and a hardened exoskeleton suited to rolling defense.

When threatened, Glomerida coil tightly into a ball, tucking the head and legs inside and presenting a protective outer surface. They possess ozopores that secrete defensive chemicals, and their sensory structures are adapted to a life in moist, shaded microhabitats.

Ecologically, Glomerida are detritivores, feeding on decaying leaf litter, wood, and other plant matter. They inhabit moist environments such as leaf litter, rotting logs, and soil across tropical to temperate regions, and they tend to avoid desiccation and bright light. They are distributed worldwide in suitable habitats, with European, Asian, African, and American representatives, including familiar species such as Glomeris marginata.

Reproduction is sexual, with males typically bearing specialized structures (gonopods) for sperm transfer. Eggs are laid in soil or concealed leaf litter, and juveniles hatch as small adults and mature through molts. The fossil record for Glomerida extends into the Paleozoic, contributing to our understanding of millipede evolution, and they remain distinct from Sphaerotheriida despite sharing the ball-rolling habit.