Convergence

We thought it was snow at first.

That didn't last long. It came down like it, at least, chaff falling from the sky nearly in sheets, but it was warm, global, and, to our growing horror, alive. Every flake a living being. DNA like Earth's, but loaded with mercury, so much that everyone had to stick to canned food while factories and processing plants got their systems cleaned.

The fall stopped abruptly and worldwide, a few days after it started, stacked an almost consistent twelve feet high. Scientists looked at the things and dubbed them astroplankton (in what a friend of mine later told me was, while also an accurate description of the things, also a nod to the ways their earthly namesakes had always been anthropomorphized), told us they were cycloptic, biology almost like our sea life but only in a sense of vague metaphor - see, this part takes in nitrogen, almost like a gill! These limbs twitch to drive it towards mercury, like a horse to water! But, of course, we couldn't make them drink. We never saw any of them eat in captivity, and the world would've forgotten all about the organisms, no part of their biology useful to science, if not for the mounds still too plentiful to sweep away and destroy.

The sun baked the upper layers to sand, but the first to fall were protected, feeding on the biomass of their younger siblings while we ignored them like they were just fading slush.

The first Metamorphosis Event occurred suddenly and without warning. The mounds imploded as the living astroplankton, now in their second stage of growth, performed a mass exodus of disgust, spilling out at ground level and traveling away from any source of heat their weak senses could pick up. Nobody saw hide nor hair of them, save for some scientists who had captured some short-lived specimens, until cavers discovered rubbery chrysalides - the results of the second Event - hidden near the surface of icy caves, and more still deeper down. Scientists couldn't pierce the flesh, either with knives and saws or with X-ray machines - so we didn't know what to expect from the final event.

The good news, though, is we finally had an astroplankton metamorphose in captivity.

It happened, again, nearly simultaneously. Biologists and connoisseurs of the strange figured it out first, realizing that the comparisons to earthly plankton weren't too far off - although naturally, we were thinking of the wrong kind. The square-cube law caught up to our interlopers, crushing them beneath the weight of their own improbable limbs, but the damage was done. Waterways were clogged with bruised biomass, clotted fields soaked with mercurial ichor. It was apocalyptic. The old movies were right, in a way; giant bugs had indeed spelled our doom, but not in the manner of Them, or of the Eight Legged Freaks; more like a meteor, an impersonal disaster with no malevolence in it.

Humanity held on, but barely; the few regions free of the bodies are still hotly contested.

Those with poetic or scientific minds would later liken the event to the world contracting cancer.

Those who spoke more bluntly, or would-be comedians, or simply those who didn't feel the need to be clinical, would more often say we got crabs.