Terrestrials are simply insects — or their larvae – that live on land. They include grasshoppers, caterpillars, beetles, hawthorn flies, black gnats and daddy-long-legs – and various other creatures such as spiders – that accidentally get blown on to the waters of a river or lake.
Most aquatic or semi-aquatic insects have ways of avoiding predators. But because terrestrial insects are land-based, they are in an alien environment as soon as they touch water. On both still and running water they make up an important part of the trout’s diet, especially in summer and autumn. Most trout and grayling are opportunist feeders, ready to snap up any victim which becomes trapped on the surface, terrestrials included.
Over the years fly-tying enthusiasts have created a vast range of creative and effective patterns. They are often well hackled and incorporate buoyant materials to help them float in fast-flowing river water.
Although some species of daddy-long-legs are aquatic in the early stages of life, the most common ones have larvae known as leather-jackets -grey-coloured grubs which munch away on the roots of grasses and flowering plants. You can certainly find adult daddy-longlegs throughout the trout fishing season. But as the summer comes to an end, the first cooling winds of autumn blow large numbers of these insects on to the water. It may take a little time for the trout to adjust to the daddy’s size and shape, but once they do, watch out!
Tackle daddy-feeding trout with a floating fly line and a suitable imitation which includes long trailing legs and a bushy hackle.
The hawthorn fly is another important terrestrial. It is a weak-flying insect, easily blown on to water by moderate spring or summer breezes. In some respects, this fly resembles an emaciated bluebottle.
During their main hatching period in April the male flies dance in loose clouds over vegetation on the waterside, looking for mating partners. Anglers generally fish with an imitation which has trailing black legs to represent the male. Trout which are feeding on terrestrials are looking for creatures trapped in the surface film, and an imitation which fits this profile is the one most likely to succeed.
A floating line and a light leader of perhaps 2-4 lb are the ideal combination for summertime angling with terrestrials. But remember that when fishing with daddy-long-legs imitations, you might want to use up to 6 lb monofilament line as a precaution against smash takes.