Overview
The Colletidae are recognised as a subfamily of Apidae in Michener (2000) and in the Lucid identification key on this website.
The following text is from Naumann (1991).
This family is better represented in Australia than in any other region. Its members range from large, robust, hairy bees to some of the smallest, most slender and barest in the world. They are usually readily recognisable by the short broad glossa which may be truncate, emarginate or bifid (in males of a few Hylaeinae it is acute apically).
Colletidae are unique among bees in that they line their brood cells (and sometimes other parts of the nest) with a colourless, cellophane-like material. This is a polyester formed from a liquid apparently secreted by the abdominal Dufour's gland (or thoracic salivary gland in Hylaeinae) and applied by the brush-like glossa of the female (Batra 1980). As far as known, all members of the family are solitary and none is parasitic except perhaps a few Hawaiian species.
Two subfamilies not represented in Australia are the Western Hemisphere Diphaglossinae and Xeromelissinae (= Chilicolinae).
Several Australian species have either the labial or maxillary palps enlarged (in some cases extraordinarily elongated) as an aid for collecting nectar from flowers with deeply recessed nectaries (Houston 1983a).
Further information about the Apidae can be found in Melo & Goncalves 2005, Michener 1965, Michener 2000 and Naumann 1991.