INSECTS IN THE HIGHLANDS
by Ed Herbst
The streams and rivers in the Highlands are extremely nutrient-rich, so not only are there numerous food forms upon which fish prey, but they occur in abundance. This accounts for the many trophy trout and yellowfish the region produces. An important point though, is that you don’t need to imitate a multitude of different insect species to fish successfully. Knowledge of the basics in aquatic entomology is, however, useful.
All the main mayfly types, the clingers, crawlers, swimmers and burrowers, are found in abundance in the streams. There are fewer mayfly species in still waters, but they do occur prolifically at times – such as during a Caenis hatch – when they can cause avid, selective feeding. The most prolific mayfly species in streams and rivers are the Baetis family, especially Baetis harrisoni and Demoreptus natatensis while the tiny Tricorythidae discolor, aptly known as the “Angler’s Curse”, hatches in clouds over dams and the slower, silt-bottomed sections of these rivers.
Caddis (Tricoptera spp)
Caddis flies are an important food source for trout and yellowish, both in the larval and pupal stages as well as adult flies. In the Highlands, the most commonly found caddis is Cheumatopsyche afia which, incidentally, is highly variable in colour. Remember that adults tend to
skitter across the water once hatched so, under such circumstances, a twitched fly often works well.
Leaf-eating Beetles (Chrysomilidae)
It is rare that a trout’s stomach does not contain a beetle and they are known to take beetle patterns opportunistically even when selectively feeding during a heavy mayfly or caddis hatch. By far the most common beetle in the Highlands is the bronze-green, leaf-eating Chrysomilidae beetle that is found in great numbers in October and November, but also in late summer and autumn. The black, mite-like larvae feed on willow leaves for two to four weeks and then pupate, emerging as mature green beetles about half a centimetre long.
Sawfly (Nematus oligospilus)
Sawflies first appear in late October and are found until autumn. A relatively recent newcomer from America, the sawfly was accidentally introduced into Lesotho in a plant consignment and was first recorded in Maseru in 1993. They subsequently spread to South Africa. Here, their host-specific food source, the imported willows, Salix babylonica and S. fragilis, had been imported to Parys in 1906 in the hopes of starting a basket weaving industry. In the absence of any indigenous biological control organisms these trees rapidly colonised high altitude streams providing the newly-arrived sawfly – a primitive form of wasp – with an almost unlimited food supply. The larvae of the sawfly, a green caterpillar, incorrectly given the generic name “inchworms” by anglers, has introduced a significant new food source for trout and yellowfish resulting in bigger fish in better condition. An examination of fish stomach contents, particularly those caught between heavily wooded banks, show that fish feed almost solely on this insect at times.
In the late afternoon, midges hovering over the water can play a significant role in the “evening rise” on streams and, on dams, emerging midge pupae can provide frenetic activity as the sun sets. They are by far the most important food source for trout in dams but they are of relatively minor importance to the river fly fisher, other than in high altitude streams where hatches of the Net-winged midges, Blepharoceridae, are prolific at times.
Dragon and damselfly nymphs are present in rivers and dams throughout the season and form a significant part of both trout and yellowfish diet, though they are more abundant and available in stillwaters than in streams.
The presence of grasshoppers, beetles and ants, like any other insect, is cyclical but, whenever they occur, they are attractive to trout and worth imitating. Most fly fishers in the Highlands tend to use a nymph, fished dead-drift behind a yarn strike indicator as an imitation of the dominant food source for fish in the region – mayfly nymphs – while striving at all times to get a drag-free drift. Fishing a hopper can offer a welcome relief from the rigours of concentrating on drag-free drifts – you can slap it down on the water surface and, when it starts to drag, you can twitch it like a small popper because that is how hoppers behave when they land in the water. They drift for a while and then kick frantically towards the bank.
Published courtesy of the Wild Trout Association