Trichoptera larvae that construct portable cases occur worldwide, in some groups building highly distinctive cases. Fifth instar larvae of several genera in the micro-caddisfly family Hydroptilidae always build cases of the same form, thus affording ready identification of their larvae and pupae to genus level. Examples are Oxyethira and Orthotrichia: the former have transparent flask-shaped silk (secretion) cases, the latter ‘wheat seed’-shaped silk cases that are generally dark brown to black in colour. Additionally, in the fauna of mainland Australia, cases of the endemic genus Orphninotrichia are unmistakable in form; enigmatically, however, quite different forms are seen in two of the four locally endemic species on the small, off-shore, oceanic island of Lord Howe. The larval cases of some other Australian genera also vary considerably, some in materials (e.g., Hydroptila) and others in both materials and shape (e.g., Hellyethira and an Australian endemic genus, Maydenoptila). Known larvae of microcaddisfly species in the Australian fauna are examined in search of patterns in the three most obviously variable attributes of cases: mode of construction, shape, and materials. Possible relationships between form and function are postulated for some of the cases.
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