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Entomology

Backswimmers & Boatmen

These guys kick ass, bite back, and trout love 'em.

Silver slashes reflect off the glass of the scuba mask. If I turn just a little, the scintillation tickle my peripheral vision and my eyes reflexively jerk toward them. The sparks are hard to ignore.

Rolling on my back, I watch the abstract flashes turn into silver bullets reigning terror in the otherwise pastoral setting of the trout pond.

Backswimmers hold silently in the film, their tails breaking the surface to feed on fresh air. The black compound eyes look painted on, uncomfortably similar to those of the Roswell aliens. The unblinking eyes survey the domain beneath them searching for predators and prey. I wonder into which category I’ve been filed.

A small water beetle scuttles amid the sedge roots and a backswimmer breaks off the film like a falcon from the clouds. With three powerful strokes of it’s paddle shaped legs, the swimmer is to the bottom of the pond in pursuit of the beetle.
The beetle scurries clockwise around the roots as it senses its impending demise. The backswimmer is not easily dissuaded. The right paddle is held aloft while the left one strokes and the swimmer pirouettes right and vectors in for the kill. At the moment of contact, a pair of raptorial claws unfold beneath the swimmer’s chin and engage the hapless beetle in their spiny grasp. Immediately, the razor sharp beak of the swimmer pierces the soft connective tissues between the beetle’s head and thorax. As digestive juices are pumped into the dying beetle, the backswimmer and its prey are buoyed gently to the surface by the swimmer’s glistening packet of air.

Backswimmers and water boatmen are members of the order Hemiptera. The most noticeable difference between the two is that water boatmen swim on their tummies and backswimmers don’t. On closer inspection, the backswimmers have a segmented, sharply pointed beak admirably suited for piercing the bodies of their prey. Water boatmen, being not strictly carnivores, have a kinder, gentler rounded beak. Both bugs can and will, however, draw blood from the relatively soft flesh of a human being.

Humans have been known to bite back. In Mexico, toasted backswimmers, called ahuautle, are eaten like pumpkinseeds and in Asia both backswimmers and boatmen are considered delicacies. In the States, we are content to use the dried and ground up bugs as turtle and aquarium fish food. Trout also know that boatmen and backswimmers taste good. In fact, they taste so good that at times fish will feed on them to the exclusion of all else.

One of the more perplexing hatches I’ve ever encountered was at a fertile lake in the extreme northeastern corner of California. The water was literally boiling with trout. The grabs were splashy and some truly huge fish were leaving toilet bowl swirls. Amid all the trout, the water was getting pocked and dimpled as if we were in a hailstorm. I was smart enough to know that under the cloudless autumn skies we weren’t experiencing hail, but I wasn’t smart enough to have brought a seine out in the boat.

For a frustrating hour and a half we flailed and failed in our attempts to seduce a fish. We tried every kind of nymph, streamer, emerger, and dry fly in our box. The only thing we apparently didn’t try was the fly that might work. It was almost a relief when the rise finally stopped and we could go back to camp.

On the row home, a lone fish sucked in the trolled leech and told us the tale. The belly was distended as if the trout had eaten a hardball. Pine nut sized backswimmers, many still flipping wildly, spilled out of its mouth. The mystery was solved, and, like most mysteries the answer should have been obvious all along. The hail was actually a blitz of migrating backswimmers.

Both backswimmers and boatmen are strong fliers and will travel great distances to redistribute themselves. Their affinity for bright light and shimmering bodies of water make suburban swimming pools equipped with underwater lamps irresistible targets of their affection. Once located in a new water, the male boatmen will make lurid song by scratching their rasping legs against the sides of their face. Their presence, thus announced, presumably establishes territory and seduces lusty water boatwomen.

The next evening the "hail" started to fall once again, and once again the surface came alive. We took light brown Birds Nests, rubbed them in dry fly floatant powder and fed them to the trout. A small split shot was required to keep the buoyant nymphs submerged as we swam them to the boat. It was a journey the nymphs seldom made without getting clobbered.
Both backswimmers and water boatmen breath oxygen from a bubble they carry with themselves. This bubble, called a plastron, clings tightly to a dense pad of unwettable hairs on the bug’s abdomen. A second, lesser bubble is carried between the body and its wings. From above, these drab insects look like drab insects; however, from underwater these bubble encrusted beasts glisten like jewels.

A waterboatman and its shiny air-filled plastron

Unlike trout, many anglers key in on the oar-like legs of the backswimmers and go to great effort to replicate these structures. Trout are generally unimpressed with the angler’s efforts and much prefer to eat any old generic nymph that sparkles, or better yet, carries a bubble of air.

A Birds Nest rubbed in powdered floatant is about as a close a clone as you’ll ever find in the world of insect imitations. The floatant keeps the Birds Nest in the film. A small split shot a few inches down leader won’t be enough weight to submerge the Nest but will be enough to pull the head under so the fly rests canted in the water just like the natural does as it gathers surface air.

A sharp tug on the flyline will cause the Nest to dive and an erratic retrieve gives a pretty darn good rendition of a backswimmer jinking about. Pause and give the line some slack and the air encrusted nymph drifts back to the surface for another breath of fresh air. Perfect.