The Lepidoptera, butterflies and moths*, are one of the most familiar groups of insects, and have the enviable advantage of tending to receive a more favourable response from the general public than other insects do. Some Lepidoptera, particularly the butterflies, are almost treated as honorary vertebrates - they receive a degree of attention and enthusiasm usually reserved for those animals of a more endoskeletal disposition. You might be forgiven, then, for assuming that the Lepidoptera are overall a well-known and studied order - but you'd still be wrong.
*Though in our lab, they tend to get referred to simply as "leps".
Traditionally, Lepidoptera have been divided into two, reasonably self-explanatory, groups - the microlepidoptera and macrolepidoptera. Though originally divided simply by size, the terms have been redefined in recent years on a phylogenetic basis - the name Macrolepidoptera has been attached to a particular clade, while leps outside this clade are dubbed microlepidoptera. The intuitive meanings of the names still work reasonably well - the majority of large Lepidoptera are indeed Macrolepidoptera (though the often very sizeable Hepialidae are, phylogenetically speaking, microlepidoptera). And, not surprisingly, it is the Macrolepidoptera that get most of the attention, while the microleps (which, just to make the point, probably constitute the greater part of lepidopteran diversity) tend to get shoved to one side.
The Gelechioidea are a large microlepidopteran superfamily. They are spectacularly diverse - Hodges (1998) referred to there being well over 16,000 described species. As if this wasn't impressive enough, perhaps only about a quarter of the world's gelechioids have been described. Most of the Gelechioidea are extremely small - one of the largest, Cryptophasa setiotricha, is 25 mm long, while one of the smallest is Siskiwitia falcata, a mere two millimetres in length (Hodges, 1998). Like many other tiny moths, the wings often have a long fringe of hairs. The larvae of gelechioids are usually retiring herbivores, often concealing themselves in a web of silk or binding leaves to form a hide. Some are detritivores or fungivores, while a few have become carnivores of other insects such as scales (Kaila, 2004). The monophyly of the Gelechioidea is not certain - the morphological analysis of Kaila (2004) supported gelechioid monophyly, but three of the four supporting characters were homoplasious with other Lepidoptera, while the only character unique to Gelechioidea (antennae meeting mesally in the pupa) had been lost in a number of gelechioid subgroups.
Homoplasy was similarly rife within the superfamily itself. Kaila (2004) resolved two major clades, a "gelechiid lineage" including (among others) the Gelechiidae, Cosmopterigidae and Coleophoridae, and an "oecophorid lineage" with the Xyloryctidae, Oecophoridae and Elachistidae, but both were supported solely by homoplasious characters. Bucheli & Wenzel (2005) used molecular data as well as morphology, but included less taxa in their analysis than Kaila (2004) - they continued to support the oecophorid lineage, but resolved the gelechiid lineage as paraphyletic. Probably as a result of such rampant homoplasy, no two revisions have agreed on the best way to divide the gelechioids into families - the major families listed are fairly safe, but various minor "family-type groups" move in and out of them at will.
Relatively few gelechioids are of economic significance to humans. A few are plant pests (such as Pectinophora gossypiella, the cotton bollworm) or can feed on stored grain or textiles, but for the most part they are just as retiring as they look. There's still an awful lot of them, though.
Bucheli, S. R., & J. Wenzel. 2005. Gelechioidea (Insecta: Lepidoptera) systematics: A reexamination using combined morphology and mitochondrial DNA data. Molecular Phylogenetics and Evolution 35 (2): 380-394.
Hodges, R.W., 1998. The Gelechioidea. In Lepidoptera: Moths and Butterflies (N. P. Kristensen, ed.) pp. 131–158. Walter de Gruyter, Berlin and New York.
Kaila, L. 2004. Phylogeny of the superfamily Gelechioidea (Lepidoptera: Ditrysia): an exemplar approach. Cladistics 20 (4): 303-340.