
Useful websites
Useful books
All taxonomical guides published by the Freshwater Biological Association (see link)
Oscoz, J., Galicia, D. & Miranda, R. (eds.) (2011) Identification Guide of Freshwater Macroinvertebrates of Spain. Springer, Switzerland.
Tachet, H., Richoux, P., Bournaud, M. & Usseglio-Polatera, P. (eds.) (2010) Invertébrés d'Eau Douce: Systématique, Biologie, Écologie. Freshwater Invertebrates: Systematics, Biology, Ecology. 2nd edition. Centre National de la Recherche Scientifique, Paris.
Nilsson, A. (ed.) (2005) Aquatic Insects of North Europe. A Taxonomic Handbook. Volumes 1 and 2. Apollo Books, Vester Skerninge (Denmark).
Böcher, J., Kristensen, N.P., Pape, T. & Vilhelmsen, L. (eds.) (2015) The Greenland Entomofauna. An Identification Manual of Insects, Spiders and their Allies. Fauna Entomologica Scandinavica. Volume: 44. Brill, Leiden (the Netherlands).
Free resources
World
Africa
Gerber, A. & Gabriel, M.J.M. (2002) Illustrations from A guide to the identification of aquatic invertebrates in South African Rivers
Europe
Wallace, I. (2003) The Beginner’s Guide to Caddis (Order Trichoptera)
Out of print handbooks from the Royal Entomological Society (Diptera, Hymenoptera, Coleoptera and many more!)
Opal Freshwater Macroinvertebrate Basic Guide
Mike's Insect Keys (amazing website with loads of free guides!)
NNSS GB non-native species secretariat: invasive species ID sheets