It is among the smallest hummingbirds and birds overall with a total length of about 9 cm (3.5 in) and a weight of 2.5–3.5 g (0.09–0.12 oz).[3] It is olive-green above with orange-ochraceous uppertail coverts and underparts (the belly often is greyer). As most other hermits, it has a long decurved bill, elongated central rectrices with whitish tips and a blackish mask bordered by a whitish-buffmalar and supercilium. The upper mandible is black, the lower is yellow with a black tip. The male has a slightly darker throat than the female.
The males form communal leks where they sing and flash their tails to attract the females. The song varies over its range, but typically is high, squeaky, complex and repeated again and again.
The little hermit lays two eggs in a conical nest suspended under a large leaf. Incubation and fledging period not reported, but probably as relatives where incubations is 14–16 days, and fledging another 20–23 days.
ffrench, Richard (1991). A Guide to the Birds of Trinidad and Tobago (2nd ed.). Comstock Publishing. ISBN0-8014-9792-2.
Hinkelmann, C. (1999). Little Hermit (Phaethornis longuemareus). pp. 545–546 in: del Hoyo, J., Elliott, A. & Sargatal, J. eds (1999). Handbook of the Birds of the World. Vol. 5. Barn-owls to Hummingbirds. Lynx Edicions, Barcelona. ISBN84-87334-25-3.