Gray treefrogs call through the longest nights

The air holds its warmth past ten o'clock near Asheville, and from the wetlands comes a sound like distant machinery. Gray treefrogs have emerged from their daytime roosts in the bark crevices and hollow stems where their mottled skin renders them invisible. Now, as darkness settles over the ponds and slow streams, the males position themselves on low branches and begin their territorial calls.

The gray treefrog spends most of its life as a solitary hunter, climbing through shrubs and low trees with the adhesive pads on its toes. Its skin shifts from gray to green to brown, matching whatever surface it rests against during the day. But early summer transforms these cryptic climbers into something else entirely. The males gather at the water's edge, their throat sacs inflating like pale balloons as they produce their prolonged trills. Each call lasts several seconds, a steady vibration that carries across the water and through the humid air.

This timing connects to more than just the calendar. Aquatic insects are emerging from the ponds and streams in waves during these longest days. Midges, mayflies, and caddisflies complete their underwater larval stages and rise to the surface, where they molt into their winged adult forms. The gray treefrogs feed heavily on these emerging insects, building the energy reserves they need for breeding. More importantly, the same insect emergence will sustain their tadpoles once the eggs are laid and hatched. The female treefrogs deposit their eggs in shallow, temporary pools where the water warms quickly and algae blooms provide food for the developing larvae. These pools teem with the same aquatic invertebrates that drew the adults to breed here.

Green frogs call from deeper water nearby, their single-note banjo twangs punctuating the treefrogs' sustained trills. The two species partition the acoustic space, the green frogs calling from permanent ponds while the gray treefrogs choose the shallower, more temporary waters. Each species times its breeding to match the peak availability of different food sources. The green frog tadpoles will overwinter in the deep water, feeding on detritus and algae through the cold months. The gray treefrog tadpoles must complete their entire development before their shallow pools dry up or freeze, racing through metamorphosis in a matter of weeks.

The calls continue past midnight, when the air finally begins to cool and dew starts to form on the grass stems. If you step outside now, the mechanical trill of the gray treefrogs carries across the darkness, steady and insistent, marking the peak of their brief breeding window in the longest nights of the year.