Psocodea

Psocodea is an insect order comprising barklice, booklice, and parasitic lice. Its members range from free-living species that feed on fungi or debris to highly specialized parasites of birds and mammals.

Psocids: Psocids are free-living insects in the barklouse and booklouse lineages, feeding mainly on fungi, algae, and organic debris. They represent the free-living branches of Psocodea.
Chewing mouthparts: Chewing mouthparts are insect structures adapted to bite and grind solid food. Many free-living psocodeans use them to scrape or consume microscopic food and debris.
Psocoptera: Psocoptera was the traditional order for free-living barklice and booklice, before parasitic lice were included in Psocodea. Its former separation from lice obscured the order’s evolutionary unity.
Human head louse: The human head louse is an obligate ectoparasite that feeds on human blood and lives on scalp hair. It is a medically relevant psocodean encountered in public-health control.
Common barklouse: The common barklouse, Psocus species, is a free-living psocid often seen in groups on tree trunks. It illustrates the conspicuous bark-dwelling side of Psocodea.
Barklice: Barklice are mostly free-living psocodeans commonly found on tree bark, foliage, and other surfaces. They are a familiar outdoor form of the order.
Phthiraptera–Psocoptera hypothesis: The Phthiraptera–Psocoptera hypothesis proposes that parasitic lice evolved from within the free-living psocopteran lineage. It describes the evolutionary relationship that unites the order’s contrasting lifestyles.
Louse evolution: Louse evolution is the history of diversification among parasitic insects adapted to birds and mammals. It traces how one lineage within Psocodea acquired obligate parasitism.
Human body louse: The human body louse is an ectoparasite that lives and lays eggs mainly in clothing, visiting skin to feed. It links louse biology to disease transmission and hygiene.
Liposcelis bostrychophila: Liposcelis bostrychophila is a small booklouse associated with stored products and indoor environments. It is a practical example of booklice in human-made habitats.

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