Redrock Stonefly: Itty, Bitty Bug Survives In A Ferocious World

Report concludes nymph found in Rim Country stream not endangered despite lurking dangers


A ferocious stream-dwelling insect no bigger than a paper staple faces all manner of threats — but little danger of extinction, the U.S. Fish and Wildlife Service has concluded after pondering the matter for four years.


Pete Aleshire/Roundup

The Redrock Stonefly isn’t endangered after all, the U.S. Fish and Wildlife Service concluded, after finding the little nymph beloved by fly-fishermen in Tonto Creek (above) and five other streams. The tiny creature favors riffles like this stretch of Tonto Creek, where it stalks creatures smaller than itself and deploys ingenious defenses against crawfish, trout and other predators.

The Redrock Stonefly lives in Rim Country’s Tonto Creek and maybe the East Verde, Dude Creek and Canyon Creek. Other populations persist in the Campbell Blue River near Alpine, Spring Creek near Young and both Oak Creek and Wet Beaver Creek near Sedona.

WildEarth Guardians asked the U.S. Fish and Wildlife Service to put the stonefly on the endangered species list back in 2007. At that time, biologists thought the stonefly lived in only a couple stretches of Oak Creek. But subsequent surveys found the hardy little critter living at 10 sites in five streams.

The federal findings mean the stonefly won’t be added to the already daunting list of creatures whose plight would require extra protections any time a federal action seems likely to affect streams in the Rim Country —especially any project affecting Tonto Creek, one of the most popular fishing and recreational streams in the state.

The status review released by the Fish and Wildlife Service presented a fascinating glimpse of the complex world of tooth and pincer in which the stonefly hunts, hides and adapts.

The Redrock Stonefly spends about three years as an underwater nymph, hiding out in the rock-covered stream bottoms by day and hunting even smaller insects and invertebrates by night. The nymphs eventually undergo a startling metamorphosis and emerge from the water in a winged incarnation, so single-mindedly focused on mating that they can’t even eat and die within days — hopefully after getting lucky.

As underwater nymphs, they creep about on the bottom, fierce as tigers to all manner of smaller critters. However, if they get dislodged from the bottom by a flood, the strike of a passing camper’s boot or the lurch of a hunting crayfish, they wind up drifting helplessly above the bottom — where they become tasty fish food.

That’s why a canny fly fisherman working Tonto Creek would do well to tie on a fly that resembles the yellow and brown nymph, bristling with small spines. If they want to be obsessive about it — they could put two eyes on the top of the little dear’s head — which distinguishes the Redrock Stonefly from its mostly three-eyed relatives. The ancestors of the Redrock Stonefly left the tropics to colonize North America some 4 millions years ago, but since the last Ice Age have evolved into many different species isolated in myriad streams.

Environmentalists hoped that the listing of the stonefly would give them one more tool to protect battered streamside habitats in central Arizona. These riparian areas remain essential to some stage of the life cycle of the vast majority of species in the state. However, dams and diversions have degraded or destroyed an estimated 90 percent of the riparian areas in the state.

The Endangered Species Act requires the U.S. Fish and Wildlife Service to designate “critical habitat” for any species in danger of extinction. This compels federal agencies like the U.S. Forest Service to consider the effects of any project that will affect that critical habitat.

However, the Fish and Wildlife Service concluded the Redrock Stonefly has proven so adaptable and resourceful that it faces no dire threat from pollution, wildfires, intense recreation use, non-native fish or even the plague of lobster-like crayfish — the introduced bane of many Arizona streams. In fact, the most serious, but ultimately imponderable, threat the biologists foresaw was climate change already under way likely to result in longer droughts and worse floods that will dry up or drastically change many Arizona streams.

But in the meantime, the stonefly has evolved marvelous counters to the dangers it faces.

Biologists found the stonefly at four sites on Tonto Creek, including both above and below Bear Flat and where Christopher Creek and Haigler Creek connect.


Fish and Wildlife Service/Caitlin Smith

The Redrock Stonefly spends three years in nymph form before taking wing to mate.

For instance, Tonto Creek has suffered from bacterial pollution — perhaps as a result of the leakage of septic tanks buried along its banks and perhaps from the impact of cows and campers.

However, even though most stonefly species in North America live in high, clear, cascading, oxygen-rich streams, the Redrock Stonefly can apparently handle muddy streams with high bacterial counts, suspending their growth, going into what amounts to hibernation or burying themselves in the mud in response to low oxygen levels or even the temporary drying up of the stream.

The biologists concluded that cattle grazing also doesn’t pose much of a threat to the stonefly, despite the big changes uncontrolled grazing can have on a stream. Only a couple of the sites where the Redrock Stonefly live have grazing allotments.

Besides, the Redrock Stonefly’s preference for fast-flowing sections of the stream with rock bottoms will protect it from most cattle impacts.

The Redrock Stoneflies have apparently even evolved a tactic to deal with introduced crayfish, the terror of most Arizona streams if you’re as small as a stonefly nymph. The crayfish gobble up vegetation, chew up leaf litter, stir up mud and wolf down all sorts of critters smaller than themselves.

The Redrock Stonefly has evolved an ingenuous defense against crayfish, who grope for prey with their lobster-like antenna. When that antenna hits a concealed stonefly, the little nymph squirts a gush of blood on the crayfish’s sensor. The fastidiously anal retentive crayfish then stops everything to clean off its antenna and the nymph scoots away.

Wildfires and the mudflows that often follow in their wake also poses a big challenge for most stream-dwelling creatures. For instance, the mudflows and floods that rushed down Dude Creek after the Dude Fire reduced invertebrate numbers in that creek by 90 percent — at least temporarily. However, studies suggest that the Redrock Stoneflies readily shift downstream and take such deft advantage of all the other floating, dislodged creatures that their numbers can actually increase in a stream after a fire.

The stoneflies and the hundreds of other species in its wet little world do face threats from escalating urban development, since groundwater wells too close to a stream can suck up enough water to have a dramatic effect on stream flows. Fortunately, most of the key stream stretches where the stoneflies live are either not close to urban development or protected by Forest Service water rights that guarantee a minimum in-stream flow.

Finally, the biologists concluded that the stonefly has even evolved tactics to cope with the voracious appetites of both native and introduced fish. For instance, the nymphs hide out in cobbled riverbeds by day and forage by night, when the most efficient fish predators are all tucked into their river beds for the night.

The presence of native fish like chub does reduce overall numbers of stoneflies, but not by much. The nymphs have a harder time dealing with super-efficient hunters like brown and rainbow trout.

The stoneflies face the most trouble in streams populated by fish that hunt at night by touch, including yellow bullheads in Oak Creek. Even then, the nymphs often escape by curling up into a bristle of spines and playing dead when touched by the probing whiskers of the foraging fish.

Of course, all bets are off if streams dry up or silt up as a result of a big shift in the climate that computer models suggest “is already under way.”

However, if you’re going to bet on anyone to cope — it would probably be a bug that’s already figured out how to cope with oxygen-eating bacteria, crayfish antenna, flash floods, clumsy hikers, munching cattle and hungry trout.


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