Spring signals the start of terrestrial insect falls proper. Arriving swallows, swifts and martins cash in on this abundant food source. Under the genus Bibio, insects include hawthorn flies, heather flies and black gnats.
Classed as terrestrials these insects emerge on land and as such they’re referred to as a ‘fall’- as opposed to a hatch - when alighting on the water.
Throughout winter, tucked-up underground safe from frost, their larvae develop. From spring onwards, winged adults emerge and crawl upwards through the soil to take flight at the surface. Seeking a companion, huge numbers swarm low over ground. Mating follows and often occurs on the wing. Egg bound females then search for suitable areas to lay their eggs. These eggs quickly hatch and the larvae bury themselves, continuing the life cycle.
Black gnats often mate in nearby trees and willows seem a particular favourite. Here gusty winds dislodge a gnat’s precarious foothold, whisking them away to a watery end. A tractor working the land, a farmer moving his cattle – all disturb flies, which again are quickly whipped onto the water in a strong wind. Be it river or lake, when I see this disturbance, I approach the water, fully expecting rising fish.
My experience suggests that warm spring days with light to moderate breezes produce the best action. The warmth encourages naturals to travel further and, while mating, light winds often carry unsuspecting flies out over water.
The water can be cooler than the surrounding land temperature and this possibly immobilizes insects. This is best illustrated on large reservoirs, where water temperatures can remain low well into early summer.
THESE are found almost everywhere, from heather clad headwaters and Lakeland hill tarns, down to lowland reservoirs, and even along the coast.
They may also turn up in parks and our own gardens. I frequently use the garden to predict potential insect falls. It’s in sheltered areas that these flies usually first appear. I’ve noticed black gnats in my own garden form April 12, yet the earliest I’ve recorded them on our northern waters is April 19.
In more exposed areas, prevailing winds are capable of shifting winged insects over incredible distances. So adults located on a sandy beach may have originated from land many miles away. However, black gnats seem to be more widespread in untouched upland regions possibly due to the undisturbed surroundings. While fertile pastureland attracts these insects, ploughing and other activities might expose the larvae to predators? But you can’t rule out a sighting of black gnats anywhere, so be prepared. There are several species of black gnats whose sizes vary widely.
Mostly they are between 5-7mm long. Don’t try to identify individual species, just know that the various emerging periods often overlap, which puts black gnats on the menu from mid-April to early-October.
The males have a long slender abdomen with a pronounced thorax, and trailing hind legs, which are quite noticeable but not as obvious as on hawthorns. Females have a fatter, more cylindrical shaped body with a small head.
Given sunlight, black gnats begin to show about 11am. However, cloud cover or cold winds might delay this until 2pm. Following a hard day finding a mate, insect flight usually begins to wane around 4pm and it’s all over by 5 o’clock. But, on calmer days, dead and dying insects remain trapped in the surface and trout feast on these into the evening.
The first spring falls of black gnats can be likened to ‘duffer’s fortnight’, when trout avidly feed like no tomorrow. As activity heightens into May, trout often adopt a more casual feeding pattern. Gone are the splashed rises and we have to look closer for a fin breaking the surface and a flattening of the water, as trout discover that naturals are far easier to harvest when washed sub-surface.
Summer gnat falls usually ebb away with a hot spell, often bringing about an quick end to big falls.
Sure, there will be some flies about, usually on cooler, comfortable days. In fact, Saturday July 30, 2005 saw a heavy fall of fly and despite the uncomfortably warm conditions, trout were quick to respond. The return of cooler temperatures in late August often encourages gnats to gather again in numbers. Continuing throughout September and early October I have experienced some of the season’s finest sport during autumn.
HAWTHORN & HEATHER FLIES
TRADITIONALLY, hawthorn flies begin appearing around St. Marks Day on April 25. In Cumbria it’s generally the first week of May but do consider geographic location, as southern regions may be a few weeks ahead of northern climes.
Far larger than black gnats, adult hawthorn flies are up to 12mm long. Their flight period lasts between 2-3 weeks and they tend to congregate around shrubs and bushes with the hawthorn tree a favourite. The trailing hind legs are a give away, and more noticeably in the males.
Heather flies are very similar in appearance and size to hawthorn flies, one major difference being the distinctive reddish-orange markings of their legs. They’re most at home on heather moorland and upland areas. They generally appear from July through to early September.
An upland water, Stocks Reservoir in Lancashire, is a known venue for heather fly falls. August is the month to expect them here.
Ungainly fliers, both these species are readily blown onto the water. Being that much larger than gnats, in their bid for freedom they can create quite a disturbance. It’s worth considering this when tying and presenting imitations. Flies with rubber legs or larger hackles that are tweaked back often get takes.
Tackle choice is a personal thing, here’s what works for me. For out and out dry fly fishing an Orvis T3 9ft 6-weight is my favourite, even from the boat. I find them sweet and responsive when constantly targeting rising fish. Hit a good fall of terrestrials and there’s plenty of moving trout. That said, a longer rod may provide an edge in a good wave when working a team of wets or spiders from a drifting boat.
Despite being an advocate of the weight-forward fly line, I often revert to a double taper (DT) during terrestrial falls. Simply because a DT allows me to pick up a substantial length of line, change direction quickly and cover my intended target. With all this directional casting, a single fly is wise, otherwise you end up with a tangle.
Dry flies produce some exciting and hectic fishing especially when the naturals first appear. During the early stages of a terrestrial fall, the sheltered bank is the first port of call as this is where any flies initially touch down. Given a light breeze these insects won’t drift far, often holding the trout in this productive area. Begin by targeting rising fish with a single dry on a tapered leader of 12-14ft. Extremely supple, copolymer leaders are perfect for presenting flies on and close to the surface. Given a sparse fall, consider two dries positioned 5ft apart and search the water by fan casting.
Sometimes, you can achieve a short natural drift of the dry fly. Trout will be familiar with the direction of drifting naturals so it pays to present your flies in such a manner. From the bank, always attempt to fish your flies back with the wind.
If positioned, with a crosswind blowing, rather than cast across and downwind, pitch the flies 45 degrees upwind to produce a more natural presentation. When fishing the sheltered bank with a backwind, introduce slack line into the forward cast. Achieved this by either throwing an upward forward loop and, as this unfolds, lower the rod quickly thus collapsing the cast so that the line lands in a series of wiggles (Slack line diagram). Or, administer your usual forward cast and when the unfolded loop starts dropping to the water, check back slightly with the rod tip to produce a shockwave creating a series of ‘S’ formations in the line (Bounce cast diagram). Take care not to jolt the rod back as the line will come hurtling back towards you, landing in a tangled mess. I can’t stress enough how subtle this movement is. These presentational casts are best practised over short distances at first and executed correctly will gives the flies freedom to drift naturally until the fly line straightens completely. On difficult days this can make a real difference.
With a breeze, land borne flies soon accumulate on the downwind shore. Here, amidst the rolling waves, lifeless insects quickly drown and get tossed about. Trout are usually found very close in here, so keep well back and fish the margins. Accustomed to gorging on easy pickings beneath the waves these fish cruise parallel to the shore.
A couple of wet Hoppers/Spider patterns often produce. Space a trio of these 3ft (if using two flies then increase to 5ft) apart and fish them as you would a team of buzzers, remembering to watch the bowing line for takes. With an increased surface area, a Hopper or Bibio on the top dropper helps hold a duo of spider patterns close to the surface.
If you witness a blanket fall of terrestrials your fly seems hopeless amongst the many naturals. Now consider “breaking the code”. Don’t match the natural by exact size and colour, instead look to change either one or both of these. I remember a fall of hawthorns that became really intense. Stepping up a hook size made my fly stand out.
Finally, keep an open mind and change tactics frequently. Here’s how easily gnats can be overlooked. On the middle River Eden, August 28 last year I found rising fish beneath some shady boughs. With plenty of aphids present, on went a size 24 Greenfly pattern. Low water meant a cautious approach. By the time I’d managed two trout, unbeknown to me black gnats had started to fall. Concentrating on the rising trout, it wasn’t until a had few refusals that I bothered to stop and observe. The gnats weren’t on the water but in it. Almost sunk and barely perceptible, the only give away was their thoraxic backs making an indentation in the surface. The trout’s rise form also altered, but so preoccupied was I with aphids that I hadn’t noticed this subtle change.