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Patagonia's Untold Stories: The Strange Diversity of River Insects

At last, spring is here. As the days warm, the mountain tops shed their white cover. The accumulated winter snow awakens the tributaries that feed the rivers. Sudden rains percolate through the loose mountainside, intensifying the water flow. My packraft is inflated and ready to enter the gelid waters in search of six-legged jewels. I prepare my collecting gear and secure all other essentials inside a dry bag in my backpack. I am ready to go.

After paddling downstream, just below the waterline in the swiftest river channels, torrent midge larvae contrast in dark clusters against the light ochre-colored boulders. I have to stop and investigate. These small but mighty creatures have evolved six ventral suckers that they use to anchor their bodies to the surface of the rock.

There, in the safety of the torrent, they will shed their larval skins one last time. Their bodies begin to change, growing triangular horn-like extensions on their heads to protect the delicate gills that will provide the necessary oxygen during their transformation to adulthood.  The larvae enter into the pupa life stage, where it will undergo a radical transformation between larva and adult stages.  The recently transformed pupae (pictured below) must remain anchored to the rock’s surface for nearly two weeks to complete the abrupt change in its body structure (metamorphosis). Interestingly, not all mature larvae engage in the process. I collect a few specimens to analyze at the laboratory but must come back to check on their development.

A week later, warmer temperatures and increasing rainfall widen the river. The increased protection that the torrent provides does not come without risks. High above, the steep inclined tributaries have become unstable – erosion is imminent. A mature southern beech (Nothofagus) tree finally succumbs to decades of constant wind. The incident creates a chain of events, inciting a small-scale landslide.

The consequential details of the occurrence are hidden by a mantle of sediment, only revealed to those inhabiting the river currents.

With the departing rains, the water resides. The overwhelming evidence reveals the devastating effects of the landslide. The vast woody debris has made the river unraftable.

The boulder that was once painted with contrasting colors of pupating midges has been dislodged. In its place, a forest giant still bearing leaves continues to be punished by the current. The pupae on the boulder are long lost, only fragments of their bodies remain as evidence of their existence.

While some species struggle, others thrive. Stoneflies belonging to an ancient lineage begin to emerge. Bead-like gills on their abdominal segments reveal the remnants of an ancient past.

Metabolic changes in their development triggers a transition of vivid green and orange coloration. They are facing transformation into adulthood. Time is of the essence, they must partake in a final meal. For that, they scout the river bed in search of easy prey.

In the riffles, dislodged torrent midges struggle to get back into the rapids. The calm water is a dangerous place to be, for their slow locomotion makes them an easy target. The fate of one of the displaced torrent midges has been sealed. A multicolored stonefly nymph walks back towards the edge of the river to consume its prey. Next to the ongoing occurrence, in the safety of the river rocks just below the water surface, a predatory mayfly awaits dusk for the opportunity to perform on the stage of the freshwater life cycle in Patagonia.

 

Such is the drive for existence and the battle for survival taking place in the waterways of southern Chile. What other secrets await discovery in the remote and pristine locations of Patagonia?

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