Aphid Day is Oct 9, 2025. I’ve been seeing a few aphids in previous days. Today they gave a nice clear signal that summer is over, swarming as soon as the sun came over the horizon. I’m especially glad to see them. This summer wasn’t hotter than average but it was harder than average on my aging body and mind.
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This is the sixteenth time I’ve noted it here. Aphid Day in 2010 was the first of Oct, in 2011 it was the end of Oct, in 2012 the first of Oct, in 2013 the last part of Oct, in 2014 (with an actual picture) the end of Sept, in 2015 end of Sept, in 2016 end of Sept, in 2017 near end of Oct, in 2018 around mid Oct, in 2019 around mid Oct., in 2020 early Nov., in 2021 Oct 3, in 2022 Oct 8., in 2023 Oct 7, in 2024 Sept 24. Now this year is Oct 9, 2025.
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Every year in Spokane the end of summer is marked by the swarming of tiny white-winged flies.
Insects don’t waste much time in adulthood; lots of bugs live several years as larvae and only a few days as adults.
These flies take it to an extreme. Adults are minimally equipped to get in the air and reproduce. They don’t have as much brain power as other flies, nor do they have hard shells. Instead of flying purposefully, they drift with the wind like seeds, and die as soon as they bump into anything even at near-zero drifting speed. Result: for a couple of days, your face and clothes are covered with semi-liquid insects.
Despite their lack of navigation, they must have some kind of superior instinct or ‘community intelligence’, because picking the last warm day is much harder than picking the first warm day of spring. Termites and ants don’t need to calculate their swarming day; they only need a simple neuron to detect when temperature rises past a certain threshold, plus an emitted pheromone to trigger the avalanche.
But how do these flies determine that today is not just warm, but the last warmth for their generation? They must be sensing something besides temperature.
At any rate, they serve as a reliable sign for us, even if our supercomputers can’t match their calculations.
Polistra has put it into folk-wisdom format:
White flies swarming, no more warming.
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[Artistic note: the swarm in the animation turned out nicely, but Polistra’s head looks steroid-swollen and South-Park-ish for unknown reasons. Maybe she’s allergic to the bugs.]
[Technical note: According to some sources, these bugs are smoky-winged ash aphids, Prociphilus americanus.]
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Polistra's Mill 