Insect life in Trysil
In May and the first half of June water levels are high and air temperatures low. The first chironomids (non-biting midges) begin to hatch in May.
Chironomids are present on the river throughout the season and regardless of what else has hatched during the day, the fish here eat more of these insects than any other kind.
The beginning of June sees the arrival of the first Baetis rhodani mayflies (also known as large dark olives) and the start of the first period of fish activity. The water is still cold, so no large fish are active yet.
The mayfly Leptophlebia marginata – well-known to those who fish with live bait – hatches in mid-June. This insect tends to attract larger fish than the Baetis flies.
Large numbers of the yellow Heptagenia mayfly (H. sulphurea and H. dalecarlica, also known as flat-headed mayflies) arrive around 20 June. These have a long hatching period which can go on through the day and night, although they tend to hatch mainly during the daytime when the temperature is milder. June also sees the arrival of Ephemerella aurivilli mayflies, whose hatching tends to coincide with that of the Heptagenia. These two hatching periods are the first to result in major, large-fish activity.
In late evenings towards the end of June it is common to come across the mass deaths of mayfly spinners that occur once they have laid their eggs. They often include several species: Ephemerella, Leptophlebia and Baetis. In June the first caddis flies also appear. These flies are small and grey, ranging between 14 and 16 in size, and belong to the Apatania family. Fish tend not to be particularly interested in these insects.
As June turns to July the first micro-caddis flies appear. They belong to the Hydroptilidae family. Their numbers are increasing and according to Olof Jakobsson from “Fluefiske i Norden” it’s uncertain whether the fish eat them at all. There tends to be no fish activity around the micro caddis-flies, but fish may eat them as they move under water to lay their eggs.
In the first half of July, sometimes earlier, the Ephemerella ignita, also known as the Blue-winged olive, hatches. Just like its larger relative, the hatching patterns for this species can vary but this fly often hatches throughout July. These flies hatch in separate parts of the river depending on their sex, resulting in only males/females being present in certain areas. The males and females are slightly different, but an imitation will do the trick for any fly-fisher.
During the first half of July we begin to spot Norway’s most common mayfly, the Baetis rhodani. This fly appears more grey than olive-coloured, but in terms of catches it doesn’t really matter which imitation you choose. This fly’s hatching period is often drowned out by that of another, larger mayfly species.
And this is the one that all fly-fishers have been waiting for. Ephemera danica – the green drake. And it is really green! This hatching generally begins around week 27 and lasts for about seven days. The hatching starts furthest south in the river, and begins in Sennsjøen about a week later. In still water areas you might also come across the Ephemera vulgata – “the drake mackerel”. The latter is also common in lakes and tarns in southern Trysil.
The brown relative of the yellow mayfly, the Heptagenia fuscugrisea, also hatches in July. This fly can be found in somewhat calmer streams than its yellow relation and are numerous in certain local areas. However, these flies hatch in smaller numbers and over a longer period of time.
Another large mayfly also hatches in the second half of July – the Siphlonurus alternatus. It is about size 10 and has brown and olive-green markings on the back part of its body. It does not hatch in large numbers, but can create great fish activity. The small Caenis mayfly, known as “the angler’s curse” is another fly that hatches here in July. Despite being numerous, they don’t generate fish activity.
Immediately after the large mayfly hatchings, the caddis flies take over as the fishes’ primary food source. Due to the varying currents and depth of the river, many species have their biotope here, and most of the mayfly family is represented. We can’t be sure how many species there are, but Olof Jakobsson believes there may be more than 100.
Free-living caddis flies (Rhyacophila nubila), net-spinning caddis flies (Arctopsyche, Hydropsyche) and many small case-building caddis flies (Brachycentrus) can be found in the more lively parts of the river. These flies are generally grey or olive green. Some species have yellow bodies and the wings are brown or grey.
There is much more variety in terms of species in the more placid parts of the river. Some of the afore-mentioned species can also be found here, although those who thrive in still water tend to dominate, for example the case-building species from the Limnephilidae family. They are generally larger, size 12 and above, and vary in colour from reddish brown and orange to beige and pale olive-green. Their wings range in colour from cinnamon-brown to beige. The large Phryganea caddis flies are also present, and their size certainly makes up for their limited number. With their chrysalis shell still attached, they can be between seven and eight centimetres long.
At some point in the middle of July the small stoneflies from the Isoperla, Xanthoperla and Siphonoperla families hatch. These flies range from size 14 to 16 and hatch freely on the water like the mayflies, and may at first glance be mistaken for them. They can generate mid-day fish activity.
In addition to the afore-mentioned insects, beetles and ants always go down a treat. Ants feature in the fish’s diet throughout the summer.
As autumn fishing is relatively new in Trysil, we do not have much knowledge of what type of insects hatch during this season. However, we can assume that it may be a new generation of Baetis and Ephemerella ignita mayflies. That has been the case in other rivers in the region, for example the Rena River.
October tends to be cold and it’s only a matter of time before the watercourses freeze over. If you’re lucky you may still experience some great days fishing for grayling if the weather is good. There are always some non-biting midges, and there are still some caddis flies about.