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The ability of some caddisflies to select calcareous and siliceous grains during case-building was tested in experimental conditions. This investigation was carried out on Hydropsyche morettii, Limnephilus flavicornis, Micropterna sequax, and Sericostoma pedemontanum; the last of these was collected in a habitat with prevalently calcareous substratum, whereas the remaining species were from marly-arenaceous ones. Larvae were provided with a substratum mixture made up of travertine and quartzite grains (1.0-1.5 mm in size forming a 1-cm-thick substratum). Apart from H. morettii, which only picks up grains in its pupal stage, the remaining species are case-builders during their larval stage. After being removed from their original case, larvae were reared in Petri dishes kept at a constant temperature of 23° C. Video camera recordings, coupled with the analysis of the number and typology of the grains incorporated into each reconstructed case, gave evidence that evicted individuals exhibited a significant preference in the picking up of grains. The Tukey test indicated, with the exception of H. morettii, a significant preference for travertine grains. Sericostoma pedemontanum preferentially selected travertine grains when reared on a mixed substratum, but it built a case using quartzite when provided exclusively with these grains. This demonstrates that the ancestral impulse to construct a protective shield prevails over the nature of the material. The preferential choice of travertine grains could be due to certain mechanical and chemical silk/grain interaction factors.

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The larvae of Drusus improvisus McLachlan, 1884, Drusus camerinus Moretti, 1981 and Drusus aprutiensis Moretti, 1981 are re-described and discussed in the context of contemporary keys of European Drusinae species. In addition, phylogenetic, zoogeographical and ecological notes are included.