Tuesday, January 18, 2011

Trichoptera, the Caddisflies

Black Dancer Caddisfly, Mystacides azurea
The Caddisflies, or Trichoptera, are present in large number on every continent bar Antartica but are relatively unknown to the general public. Outside experts, anglers are the only people who know the insects. Caddisflies are a very important food for predators such as fish and anglers imitate them with artificial lures (1). Ignorance of these small (the largest being c. 30mm (2)) insects is understandable as they are tied to water for most of their lives. The eggs, larvae and pupae are found in or very near fresh water and the adults, while aerial, are rarely found far from streams and rivers (1). It is surprising therefore to discover that surveys of streams often see more species of caddisfly than mayflies, dragon- and damsel flies and stoneflies (3). Indeed in Ireland there are more species of caddisfly, 147, than of the other three orders combined, 100 (4).
Caddisfly Larval Cases

The diversity of caddisflies has been attributed to the ecological opportunities made possible by the secretion of silk (3). Silk is used by caddisflies for a variety of uses, such as spinning catching nets and hiding tubes, construction of small domes from sand grains,using silk to stick together pieces of plants and other materials into protective cases and the spinning of cocoons (5). Such activities are carried out prior to the emergence of the adults that resemble small moths, to which they are closely related (1). They differ in that their wings are covered with hairs rather than scales (6). The diversity of caddisflies is such that they are used in palaeoecology to investigate phenomenon such as the effect of long term climate change (7).

References:
  1. Morse 2009, Trichoptera (Caddisflies) in Encyclopedia of Insects pp. 1015-1020
  2. Chinery 1997, Collins Gem Insects p. 212
  3. Mackay 1979, Annual Review of Entomology 24 pp. 185-208
  4. Ferriss et al. 2009, Irish Biodiversity: A Taxonomic Inventory of Fauna pp. 96-111
  5. Sehnal and Sutherland 2008, Prion 2 pp. 145-153
  6. Holzenthal 2009, Encyclopedia of Inland Waters pp. 456-467
  7. Williams 1988, Palaeogeography, Palaeoclimatology, Palaeoecology 62 pp. 493-500

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