Water Boatmen & Backswimmers:
Late season sleepers
In the world of predator and prey it’s good to go unnoticed when you’re the prey. For most of the year that is just what water boatmen and backswimmers manage to do. But in the late fall and early winter things change. Suddenly the little seen water boatmen and backswimmers reach their prime and become a sought after special on the fall trout’s dinner menu on most lakes and slow moving streams across the country.
So, what are water boatmen and backswimmers, and how will you know one when you see one? First, they both belong to the order Hemiptera, or “true bugs.” Most hemipterans are land lovers only venturing into water by mistake. These landlocked hemipterans include many common pests like stink bugs, plant bugs, assassin bugs, and the one bug your mother warned you of just before going to sleep – bed bugs. The number of aquatic hemipterans is small compared to the number of terrestrial species, though some are quite obvious and well known. Take water striders, or water skippers as some call them, for example. Just about any pond or quiet pool will have these masters of surface tension skating across the surface looking for small insects trapped in the surface film. Some refer to them as “Jesus” bugs for having mastered the art of walking on water. These little fellows have taken the idea of being light on your feet to the extreme. Like many other Hemiptera they posses stink glands that release a foul liquid when something tries to make them dinner. As a result even trout have learned to let them skate directly overhead unharmed. There are other interesting aquatic Hemiptera like water scorpions, and one of my all time favorites, toad bugs. World wide the order Hemiptera is divided into 74 families (45 in North America) and thousands of species, of which 300 North American species live in or on the water.
Water boatmen are in the family Corixidae, which is comprised of 18 genera and nearly 130 species in North America. Backswimmers belong to the family Notonectidae. This is a less diverse family with only three genera and 32 species in North America. Species of both families are widespread across the continent with most preferring lakes and ponds, but many others are also at home in slow moving sections of streams and rivers, especially where aquatic plants create cover from searching fish.
Recognizing water boatmen and backswimmers is relatively easy. First, all Hemiptera have piercing sucking mouthparts shaped a bit like a short straw. Water boatmen and backswimmers are no exception, except that water boatmen have a short and rounded or truncated sucking straw designed to not only suck the fluid out of algal cells, but also grind up small pieces of food. Backswimmers on the other hand are predators. Their mouthparts are longer and come to a sharp needle-like point. And beware. A backswimmer roughly held in the hand will make a point of jabbing this spear into your flesh, an experience that quickly gets him his freedom.
In action backswimmers dart after small aquatic insect larva, which they grasp with their hook-like front legs and hold on while they pierce the prey with their long sharp sucking mouthparts. At this point they inject their prey with a fluid that breaks down proteins and essentially turns the tissue of the prey into a liquid that can be easily sucked up like a slurpy. Water boatmen and backswimmers use similar habitat and routinely live side-by-side. That living arrangement works better for backswimmers than water boatmen, as water boatmen are a prime food item of backswimmers. Backswimmers eat many other types of food than just water boatmen, including midges, mayflies, damselflies, and even small fish.
Besides distinctive mouthparts, water boatmen and backswimmers have long oar-like hind legs that propel them through the water in quick jerky darts of several inches to several feet at a time. Size wise backswimmers tend to be bigger than water boatmen, though both vary from as small as 1/8 inch to over a ½ inch long depending on the species. Colors tend to favor light brown to green for camouflage purposes, but a few species of backswimmers have a bright white dorsal surface. While this may sound like an easy target for cruising fish, backswimmers are so named because they swim upside-down – their dorsal surface down and ventral surface up. As a result the white colored dorsal surface blends into the light colored background of the sky to a cruising fish looking up from below. This is the same camouflage approach used on fighter planes – dark on top and light below.
Their life cycle of water boatmen and backswimmers follow a similar progression. For most species adults over winter and usually remain active even under a canopy of ice. On one late winter fishing trip I found a well preserved water boatmen frozen in a chunk of streamside ice. It was a sunny day so I broke out the piece of ice and set in a tray in the sun. In a few minutes the ice was water and the water boatmen was swimming apparently happy spring had finally arrived. Eggs are laid in the spring and summer with more than one brood of eggs possible. Both water boatmen and backswimmer adults fly quite well, and prior to egg laying they may take off on dispersal flights looking for new waters in which to spread the offspring. After one to three weeks the eggs hatch and the young nymphs take six to eight weeks passing through five instars (an instar is a period of growth between molts) before becoming adults. Mating generally takes place in the fall, and creates another active flight period of adults. The best fishing occurs when adults are most active in the spring and fall. In the fall, when the populations are at their peek and adults active, some of the best opportunities occur for fish and observant fishermen.
The behavior of water boatmen and backswimmers creates some easy opportunities for fish to find and catch them. First, young nymphs are simply small copies of the adults in shape and behavior, they just lack fully developed wings with which to fly. Thus both stages, nymphs and adults, are aquatic and available to fish. While they live underwater their whole life, both nymphs and adults rely on surface air for their oxygen. As a result they must periodically come to the surface and grab a bubble of air that they then carry underwater like a small scuba tank. This scuba tank however has no sides and the bubble is held in place by surface tension and strategically placed hairs around the body. I’ve always liked the fact that water boatmen and backswimmers used an aqua lung for breathing underwater long before Jacque Cousteu came along. As oxygen is depleted from the bubble some oxygen from the surrounding water diffuses into the bubble allowing them to stay below the surface for several minutes before making another chancy journey through the water up to the surface for another bubble. Because of the regular trips to the surface for air, water boatmen and backswimmers do not live in very deep water. Most often they will be in water one to four feet deep. The regular trips to the surface also force them into open water where trout find them a quick and easy meal. In the fall when other food is less abundant they become that much more interesting to hungry trout.
Fly patterns for water boatmen and backswimmers are simple. Select a hook of appropriate size. In the fall this will usually be a size 12 or 14 standard length hook. Next find some dubbing or yarn for the body of the fly that matches the color of the underside of the natural and wrap it up the shank, pausing to tie in a pair of legs (pheasant tail fibers work nicely) at a right angle to the hook just forward of the middle of the fly. Finally, cover the top of the body with a shellback that matches the color of the dorsal or top side of the natural. I use light gray or olive duck quill, turkey tail, or a sheet of mylar cut to fit. You can also pull a piece of appropriately colored thin foam over the top. The value of this will become apparent when you start fishing the fly.
As fall turns to winter this year keep a sharp lookout for the surface swirls of feeding trout where nothing appears to be on the surface. When this happens look in the shallows for either water boatmen or backswimmers bobbing in the surface or diving to or from the bottom. If you see some hopefully you’ll have more than one fly in your vest that matches them, as it’s a good bet you will break a few tippets fighting the large fish that love to call water boatmen and backswimmers dinner.
Rick Hafele, a professional aquatic entomologist, not only studies aquatic insects but has also been known to eat them. And he’s not alone. Dried water boatmen adults are often sold in South American markets and eaten like peanuts.
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