These two water bugs are quite similar, with the backswimmer being the larger of the two.
Most of their life is spent underwater, grasping onto an air bubble to breathe as they search for food. They become particularly noticeable to trout and anglers when they become capable of flight, especially when they land back on the water with a noticeable ‘splat’. The main differences between them are size, shape and colour.
- grow to about I5 mm in length
- have a teardrop shaped body with dark olive undersides, white to tan backs with a wine glass shaped marking, and red eyes
- often hang near the surface, ready to ambush larvae, pupae, their smaller water boatmen cousins, and sometimes small fish
- grasp their prey and inject an enzyme to liquify its internal organs
- be careful! – they can deliver a painful bite.
- often misidentified as backswimmers but are smaller – 6 to 12 mm – much more plentiful, and don’t bite,
- are oval shaped with dark, copper coloured backs, light tan to olive bellies and prominent eyes
- are primarily vegetarians, sucking juices from algae and plants, but will occasionally feed on small larvae
- known for the high frequency sound they make at mating time and for their attraction to bright lights at night.
Both move like a rowboat, using their long legs as oars, with a jerky, “backstroke” motion. The backswimmer, as its name suggests, swims on its back and the boatman swims ‘right-side up’. Both grab a bubble of air from the surface to breathe – it can last them for up to six hours underwater – and give them a shiny appearance.
These insects can overwinter under the ice in Alberta using trapped air bubbles to breathe. Some mature adults can be seen flying soon after the ice melts. They mate underwater in the spring, lay their eggs and die off soon after. The young look just like miniature adults.
They go through five moults and reach maturity by the fall. At that stage they’re able to fly. On sunny fall days, usually in the afternoons, large numbers of backswimmers and water boatmen migrate in swarms, flying to different bodies of water nearby or to different areas of the same lake.
Unfortunately for them, this increased activity and the sound and commotion of their landing on the surface attracts fish and in turn the angler.
Backswimmers and boatmen are most active in late spring and especially in the fall. If you see what looks like ‘raindrops’, occasionally mixed with the rise form of a trout, tie on a floating, often foam-bodied, water boatman fly or a backswimmer imitation such as the Foam Swimmer.
Cast to the rises, using a floating fly line or a casting bobber, let the fly sit for a few seconds, as the naturals often do when they land back on the water, then give the fly an occasional twitch. There’s no need for a delicate presentation – these insects hit the water hard when they land. If there’s no sign of surface activity, backswimmers and boatmen may still be quite active below. Use a sinking imitation, cast or hang the fly under a strike indicator, and retrieve imitating the motion of a rowboat – short but sharp pulls on the line. Include a short pause, about five seconds, after every five or six pulls.
In deeper water, use a sinking line and swim the imitation down with the same short, quick pulls to copy the motion of the insects. Then swim it back up towards the surface. Often trout will follow the fly up and hit it just before it surfaces. Slowly trolling spinning rigs or fly lines using floating flies, sinking flies, or a backswimmer jig can also be effective, more so if the fly is given that same row boat-type action.
As backswimmer and water boatman activity often overlaps, fishing imitations of both on the same line can increase your catch rate. The least tangle-prone method is to tie three to five feet of tippet to the hook bend of a floating backswimmer using a clinch knot and a bead-head boatman to the other end. Trout often key in on one for a while, then switch to the other. For alternative methods of setting up a multi-fly rig search ‘Washing Line Technique’
Additional Links to more information:
– on backswimmer and water boatmen fly fishing strategies with fisheries biologist, author, fly tier and ambassador for BC fisheries, Brian Chan
– on fishing swimmers and boatmen at Muir Lake, Alberta with Phil Rowley and local guide, Mike Monteith.