Ptiliidae
Ptiliidae is a family of very tiny beetles with a cosmopolitan distribution. This family contains the smallest of all beetles, with a length when fully grown of . The weight is approximately 0.4 milligrams. They are colloquially called featherwing beetles, because the hindwings are narrow and feathery. The eggs are very large in comparison to the adult female (maybe half the length) so only one egg at a time can be developed and laid. Parthenogenesis is exhibited by several species. The small size has forced many species to sacrifice some of their anatomy, like the heart, crop, and gizzard. While  the exoskeleton and respiration system of the insects seems to be the major limiting factors regarding how large they can get, the limit for how small they can become appears to be related to the space required for their nervous and reproductive systems. There are approximately 600 described species in 80 genera, but large numbers of specimens in collections await description and the true number of species is likely to be much higher than this. Fossil ptiliids have been recorded from the Oligocene, roughly 30 million years ago from the Eocene, 46.2–43.5 million years ago, and from the Cretaceous Lebanese  and Burmese amber, dated to 125 and 99 million years ago, respectively. The family is divided into 3 subfamilies: Discussion of how their distinctive wing anatomy affects the speed of their flight was researched and discussed in scientific journals in 2022.