Structure and Physical and Chemical Properties of Fibres from the Fifth Larval Instar of Caddis-Flies of the Species Hydropsyche angustipennis

Caddis-flies (Trichoptera) belong to insects closely related to butterflies and, like the latter, have a gift for spinning silky floss. It is an especially attractive ability for modern science as it is looking for new natural materials applicable in human life. The aim of our study was to compare the properties of trichopteran silky floss with those of raw silk and fibres from a cobweb. Knowledge of the chemical composition and structure of these fibres, along with their micro- and macroscopic features and morphological properties, will allow to assess the usefulness of this material. It is most likely that the product from the silk glands of caddis-flies could be applied in medicine. The material of our investigations came from one of the Trichoptera species - Hydropsyche angustipennis. Fibres were taken from live advanced/matured larvae (in the 5th larval instar). The larvae were raised separately in a plastic box, without food and with a systematic water exchange in order to eliminate the influence of contamination by trichopteran excrement. Fibres of the caddis-flies investi gated were elements of their web and the lining of the pupal shelter, while the raw silk came from a Bombyx mori cocoon and the spider’s silk from a Tegenaria domestica cobweb. The investigations included identification of the material and the density of the caddis-fly fibres. Additionally, the structure of these fibres was examined by means of IR absorption spectroscopy, and the FTIR method made it possible to confirm the presence or absence of functional groups in the silky floss of various groups of invertebrates. Observations with the use of scanning electron microscopy (SEM) revealed the spatial structure and crosssectional shape of the fibres under investigation.