Cover of the book Adult Caddis (Trichoptera) of Britain and Ireland: a practical guide, showing an adult caddisfly
Adult Caddis book cover

Aquatic insects Biological recording & species identification

Ian Wallace, Sharon Flint and Peter Flint

Field Studies Council


ISBN: 9781908819758

Reviewed by Craig Macadam

Caddisflies (Trichoptera) were once considered an inconvenience when light-trapping, by-catch quickly released in favour of the real prize, the moths. Occasionally the trapper would be fooled by a look-alike, and take a closer look at the caddis, before eventually realising their mistake.

Now there is much interest in the identification of this by-catch. A Facebook group for ‘Moth Trap Intruders’ has over 1,900 members, and there are identification crib sheets for regularly encountered groups such as sexton beetles and ichneumon wasps.  

Over the years there have been a number of identification keys and guides for adult caddisflies. My dog-eared copy of ‘A Key to the Adults of British Trichoptera’ by T.T. Macan, published in 1973, has served me well over the years, however the discovery of new species to the British fauna, and improvements to identification features means that sadly the usefulness of this publication is on the wane.

The past decade has seen several attempts to popularise the identification of adult caddisflies. The Royal Entomological Society handbook by Peter Barnard and Emma Ross provided an up-to-date reference to adult caddis with, for the first time, photographs of some of the species. Whilst a useful key for more experienced entomologists, beginners often struggle with identification of some species. To address this shortcoming the Field Studies Council published a fold-out guide by the same authors featuring some of the most commonly encountered caddisflies.

More recently, the Freshwater Biological Association published family level keys to adult caddisflies by Stuart Crofts. This key was designed to introduce beginners to caddis and their identification. There was, however, still a need for an easy to understand, comprehensive identification guide to adult caddisflies. 

This new identification guide, prepared by Ian Wallace, and Sharon and Peter Flint, perfectly addresses that need. It begins with a useful introduction to studying adult caddisflies, including how to handle, examine and photograph them. It also highlights other insects that might be confused with caddisflies. While most keys focus on diagnostic features, this key takes a different approach, focusing rather on the appearance of the whole insect, with wing colouration, patterning and shape used together with the all-important leg spur and palp formulae. The identification can be confirmed in the initial keys.

The species covered in the key are split into groups based not on taxonomy, but on morphology, such as ‘very spiny legged caddis’ or ‘very long antennae caddis’. Each group is then further split into sub-groups, and then sections. This ‘say-what-you-see’ approach makes the key very easy to use. Once your specimen has been narrowed down to one of the sections, you are presented with some basic information about each species including wing length, flight period, distribution, characteristic features and similar species. For each species there are annotated photographs of the diagnostic features, together with figures of the genitalia. For particularly variable species, such as the two Halesus species, there are multiple photographs showing the variation which makes matching your specimen far easier. Whilst this isn’t a ‘standard’ type of key, I find that the approach taken works incredibly well. The layout is easy to follow and the information is clear and easy to understand. In summary, if you want to start identifying this important group of insects, whether as an angler, moth trapper, or simply to learn a new group, this publication will be the perfect accompaniment.

Cover of the book Adult Caddis (Trichoptera) of Britain and Ireland: a practical guide, showing an adult caddisfly