Pill Scarab Beetles: these beetles are covered in plates that perfectly interlock when the beetle folds its limbs, lowers its head, and curls itself into a ball
Above: Eusphaeropeltis sp. (top/bottom left) and Ceratocanthus aeneus (bottom right), two different species of pill scarab beetle
Beetles of the Ceratocanthinae subfamily (also known as pill scarab beetles) rely on a unique form of conglobation to conceal themselves. As the beetle tucks its head down and folds its legs up against its belly, the plates on its head, thorax, abdomen, and legs all come together to form a solid shield; the plates on its legs even have grooves and corresponding ridges that allow them to neatly interlock.
As this blog post explains:
Adult Ceratocanthinae are best known for their ability to conglobate: rolling into a nearly perfect ball. The elytra, pronotum, head, and all six tibiae interlock with each other by means of grooves and corresponding ridges, forming a tightly connected external surface. Many beetles take the form of a tight compact structure when threatened, however in Ceratocanthinae the tibiae of all six legs participate in forming the external hard surface of the sphere, unlike in other beetles.
Above: Ceratocanthus sp.
The Ceratocanthinae subfamily contains many different genera/species, and they are all collectively known as pill scarabs. Many of them have a colorful, metallic appearance; they may be green, red, blue, brown, black, or multicolor.
Above: Germarostes globosus
Sources & More Info:
Gil Wizen: Transformers (Ceratocanthinae Beetles)
Communications Biology: The Evolution of Conglobation in Ceratocanthinae
Arthropod Systematics and Phylogeny: Rolling into a Ball: phylogeny of the Ceratocanthinae
ZooKeys: The Ceratocanthinae of Ulu Gombak
Pavel Krásenský Photography: Scarabaeidae (this site is written in Czech)