Phthiraptera

Definition

A major clade of wingless, obligate ectoparasitic insects comprising the chewing lice (Amblycera, Ischnocera) and sucking lice (Anoplura, Rhyncophthirina). Historically ranked as an order, Phthiraptera is now treated by most authorities as the infraorder Phthiraptera within the order Psocodea, reflecting molecular evidence that lice are highly modified, parasitic descendants of free-living barklice and booklice. Members are dorsoventrally flattened, have reduced or absent eyes, and possess claws adapted for clinging to host hair or feathers.

Etymology

From Greek phtheir (louse) + apteros (wingless, from a- 'without' + pteron 'wing'), referring to the complete absence of wings in all life stages.

Example

The human head louse, Pediculus humanus capitis, and the body louse, P. h. corporis, are anopluran members of Phthiraptera; the former causes pediculosis capitis, while the latter can vector Rickettsia prowazekii (epidemic typhus) and Borrelia recurrentis (relapsing fever).

Synonyms

• lice (common name)
• sucking and chewing lice

Related Terms

• Psocodea
• Anoplura
• Amblycera
• Ischnocera
• Rhyncophthirina
• Ectoparasite
• Pediculosis
• nit
• Psocoptera

Usage Notes

Taxonomic rank is in flux: older literature treats Phthiraptera as an order co-equal with Psocodea (formerly Psocoptera), while modern phylogenetic studies subsume it as infraorder Phthiraptera within an expanded order Psocodea. The group is strictly monophyletic but paraphyletic with respect to its free-living psocodean relatives. 'Louse' (plural lice) is the vernacular equivalent; 'Phthiraptera' is preferred in formal taxonomy. Distinguish from Psocodea sensu stricto (barklice, booklice), which are non-parasitic and often retain wings.