Lycaenidae is the second-largest family of butterflies (behind Nymphalidae, brush-footed butterflies), with over 6,000 species worldwide, whose members are also called gossamer-winged butterflies. They constitute about 30% of the known butterfly species.
|The large blue, a lycaenid butterfly|
Adults are small, under 5 cm usually, and brightly coloured, sometimes with a metallic gloss.
Larvae are often flattened rather than cylindrical, with glands that may produce secretions that attract and subdue ants. Their cuticles tend to be thickened. Some larvae are capable of producing vibrations and low sounds that are transmitted through the substrates they inhabit. They use these sounds to communicate with ants.
Adult individuals often have hairy antenna-like tails complete with black and white annulated (ringed) appearance. Many species also have a spot at the base of the tail and some turn around upon landing to confuse potential predators from recognizing the true head orientation. This causes predators to approach from the true head end resulting in early visual detection.
Lycaenids are diverse in their food habits and apart from phytophagy, some of them are entomophagous, feeding on aphids, scale insects, and ant larvae. Some lycaenids even exploit their association with ants by inducing ants to feed them by regurgitation, a process called trophallaxis. Not all lycaenid butterflies need ants, but about 75% of species associate with ants, a relationship called myrmecophily. These associations can be mutualistic, parasitic, or predatory depending on the species.
In some species, larvae are attended and protected by ants while feeding on the host plant, and the ants receive sugar-rich honeydew from them, throughout the larval life, and in some species during the pupal stage. In other species, only the first few instars are spent on the plant, and the remainder of the larval lifespan is spent as a predator within the ant nest. It becomes a parasite, feeding on ant regurgitations, or a predator on the ant larvae. The caterpillars pupate inside the ants' nest and the ants continue to look after the pupae. Just before the adults emerge, the wings of the butterfly inside the pupal case detach from it, and the pupa becomes silvery. The adult butterfly emerges from the pupa after three to four weeks, still inside the ant nest. The butterfly must crawl out of the ant nest before it can expand its wings.
Several evolutionary adaptations enable these associations, including small glands on the skin of the caterpillars called "pore cupola organs". Caterpillars of many species, except those of the Riodininae, have a gland on the seventh abdominal segment that produces honeydew and is called the "dorsal nectary gland" (also called "Newcomer's gland"). An eversible organ called the "tentacular organ" is present on the eighth abdominal segment (third segment of thorax in the Riodininae) and this is cylindrical and topped with a ring of spikes and emits chemical signals which are believed to help in communicating with ants.
A few authorities still include the family Riodinidae within the Lycaenidae. The monotypic former subfamily Styginae represented by Styx infernalis from the Peruvian Andes has been placed within the subfamily Euselasiinae of the family Riodinidae.
- Lipteninae (Afrotropical) may be ranked as a tribe of Poritiinae. (Liptenini) 
- Poritiinae (Oriental and Afrotropical)
- Liphyrinae (mostly African, some Asian) may be ranked as a tribe of Miletinae. (Liphyrini)  Selected species
- Liphyra brassolis – moth butterfly (largest lycaenid)
- Curetinae – sunbeams (Oriental or Palaearctic) selected species
- Miletinae – harvesters (mostly African, or Oriental, some Holarctic), probably all feed on aphids or their secretions
- Curetis thetis – Indian sunbeam
- Theclinae – hairstreaks (usually tailed) and elfins (not tailed) (global) may be ranked as a tribe of Lycaeninae (Theclini) see the clade below right. Selected species
- Lycaeninae – coppers (Holarctic) selected species
- Polyommatinae – blues (global) selected species
- Caleta spp.
- Celastrina ladon – spring azure
- Chilades - jewel blues
- Cupido comyntas – eastern tailed-blue
- Cupido minimus – small blue
- Cyaniris semiargus – mazarine blue
- Euphilotes battoides allyni – El Segundo blue
- Euphilotes pallescens arenamontana – Sand Mountain blue
- Glaucopsyche lygdamus – silvery blue
- Glaucopsyche lygdamus palosverdesensis – Palos Verdes blue
- Glaucopsyche xerces (extinct) – Xerces blue
- Icaricia icarioides fenderi – Fender's blue
- Phengaris arion – large blue
- Phengaris xiushani
- Polyommatus icarus – common blue
- Pseudozizeeria maha – pale grass blue
- Plebejus argus – silver-studded blue
- Talicada nyseus – red pierrot
- Naomi E. Pierce, Michae, F. Braby, Alan Heath, David J. Lohman, John Mathew, Douglas B. Rand, Mark A. THE ECOLOGY AND EVOLUTION OF ANT ASSOCIATION IN THE LYCAENIDAE (LEPIDOPTERA) 47(1):259-267 
- Pierce NE, Braby MF, Heath A, Lohman DJ, Mathew J, Rand DB, Travassos MA. 2002. The ecology and evolution of ant association in the Lycaenidae (Lepidoptera.) Annual Review of Entomology 47: 733-771. PDF
- DeVries, Philip J. 1992. Singing Caterpillars, Ants and Symbiosis. Scientific American, 267:76
- Robbins, Robert K. 1981 The "False Head" Hypothesis: Predation and Wing Pattern Variation of Lycaenid Butterflies. American Naturalist, 118(5):770-775
- Australian Museum factsheets Accessed 4 November 2010 on the Wayback Machine.
- Brower, Andrew V. Z. 2008. Lycaenidae. Version 25 April 2008 (temporary).  in The Tree of Life Web Project, 
- Ackery, P. R., R. de Jong, and R. I. Vane-Wright. 1999. The butterflies: Hedyloidea, Hesperioidea, and Papilionoidea. Pages 264-300 in: Lepidoptera: Moths and Butterflies. 1. Evolution, Systematics, and Biogeography. Handbook of Zoology Vol. IV, Part 35. N. P. Kristensen, ed. De Gruyter, Berlin and New York.
- Hall J.P.W. & Harvey DJ. (2002) A survey of androconial organs in the Riodinidae (Lepidoptera). Zoological Journal of the Linnean Society, 136:171-197
- Brower, Andrew V. Z. 2007. Riodinidae Grote 1895. Metalmarks, Erycinidae Swainson 1827 (see nomenclature section). Version 19 May 2007  in The Tree of Life Web Project, 
- Scoble, MJ. 1992. The Lepidoptera: Form, Function and Diversity. Oxford University Press. ISBN 0-19-854952-0
- , Site of Markku Savela
- , Site of Markku Savela
- Charles A. Bridges, 1994. Catalogue of the family-group, genus-group and species-group names of the Riodinidae & Lycaenidae (Lepidoptera) of the world Urbana, Ill. :C.A. Bridges pdf
- Eliot, J.N.1973 The higher classification of the Lycaenidae] (Lepidoptera): a tentative arrangement. Bulletin of the British Museum (Natural History), entomology, 28: 371-505. 1973: 
- Glassberg, Jeffrey Butterflies through Binoculars, The West (2001)
- Guppy, Crispin S. and Shepard, Jon H. Butterflies of British Columbia (2001)
- James, David G. and Nunnallee, David Life Histories of Cascadia Butterflies (2011)
- Pelham, Jonathan Catalogue of the Butterflies of the United States and Canada (2008)
- Pyle, Robert Michael The Butterflies of Cascadia (2002)
|Wikimedia Commons has media related to Lycaenidae.|
|Wikispecies has information related to Lycaenidae|