August 17, 2020

Water Boatman and Backswimmer Fly-Fishing Tactics

Early fall can be a frustrating time for the stillwater fly fisher. Dropping air temperatures will start the long-awaited cooling of a lake’s water, which will trigger gradually increasing levels of activity among trout and char. The major aquatic insect hatches, save for the odd minor chironomid or mayfly emergence, are finished for the season, and the trout will now be confined to searching out those food sources that will be overwintering in the lake. These include shrimp or scuds, immature damselfly and dragonfly nymphs, leeches, and chironomid larvae (bloodworms).

There is, however, one brief flurry of aquatic insect activity that trout and char always look forward to: the mating and swarming flights of water boatmen and backswimmers. Belonging to the Order Hemiptera, these remarkable insects include both aquatic and terrestrial species.

Boatmen and backswimmers spend the majority of their lives in the aquatic environment but are air-breathers, and have the ability to fly as well. When subsurface, they store air within a plastron: a bubble of air formed over many small hairs or scales that cover their abdomens. They come to the surface periodically to recharge their air supply. Excellent swimmers, boatmen and backswimmers utilize a pair of modified hind legs to propel them quickly through the water.



Backswimmer.

Boatmen and backswimmers are usually found hiding amongst the aquatic vegetation that grows up on the shoal or shallow water areas of the lake. Here they prey upon zooplankton, shrimp, and immature mayflies, as well as bits of vegetation. Trout and char are able to feed opportunistically on boatmen and backswimmers at all times of the year, but become focussed on them when these bugs become more active and available in greater numbers.


Resting backswimmer. 


Waterboatman.

Boatmen and backswimmers are also excellent fliers. In early fall, they will go on mating flights to release eggs into other bodies of water. Typical flights occur on frosty, bright sunny days. What appear to be raindrops hitting the water are actually boatmen and/or backswimmers diving down into a lake to deposit eggs on bottom substrates.
 
Fish in a lake are attracted to the insects hitting the water and struggling momentarily before they begin their swim down through the depths. It is common to have boatmen and backswimmers landing in deep as well as shallow water. Trout and char will eat these insects as they struggle in the surface film, and as they swim up and down through the water column. This means we can fish imitations of these insects on both floating and fast-sinking fly lines.



Waterboatman on Six Mile Lake. 

Floating patterns are typically tied out of pre-shaped foam bodies which are coloured with waterproof marking pens to imitate the real insects. A pair of black or dark-brown rubber legs complete the imitation. Fish that are chasing surface boatmen and backswimmers can provide some very exciting action with dry flies. Often you can track a particular fish as it chases down the struggling insects. Cast three to five metres (10 to 15 feet) ahead of the last rise, and then begin retrieving in a series of short strips interspersed with brief pauses. The take is a large swirling riseform followed by screaming runs!

Fish will readily hunt these insects down deeper in the water. This is where you will use your type 3 to type 7 full sinking line to imitate the up-and-down swimming action of the real bugs. Shorten your leader to about 1.5 metres (five feet). Cast out a pattern as far as possible, and allow your fly line to sink. The heavier midsection of the fly line will create a belly, or U-shaped profile, of the line as it sinks. Use a seven- to 13-centimetre-long (three- to five-inch), fast-strip retrieve to imitate the insect swimming down and then back up through the water. As the fish are chasing a fleeing food source, the powerful strike will almost pull the rod out of your hand. 

The key to having success with boatman and backswimmer patterns is first recognizing what is occurring with the insects hitting the water, and then watching for the feeding activity of the fish. An even more obvious clue will be when these bugs are landing in your boat. 



Waterboatman and backswimmer flies. 

There are lots of good boatman and backswimmer patterns to tie, and they are also available at your local fly shop. Make sure you have a selection of them when you venture out on the water this fall. Encountering a flight of water boatmen and backswimmers can make for a truly memorable day on the water.




Author: Brian Chan, Freshwater Fisheries Society of BC Fishing Ambassador. 
Images: Brian Chan.