On 27 December 2024, in the quiet town of São Thomé das Letras in southeastern Brazil, hundreds of dark specks hung eerily in the sky. They drifted like snowflakes, too lazy to fall to earth, too restless to stay still.
But these were no snowflakes. They were spiders. Locals uploaded videos to social media, where they quickly went viral. For a brief moment, it seemed as though it really was ‘snowing’ spiders.
Parawixia bistriata is a thumbnail-sized orb-weaver spider found in South America. Most of the world’s 40,000 or so spider species live alone, but not P. bistriata. This is a social species. Charles Darwin is thought to have observed them in Argentina. He described “many large black spiders, with ruby-coloured marks on their backs, having gregarious habits.”
By day, hundreds of individuals huddle together among the branches, forming dense, football-sized clusters known as bivouacs. This is surrounded by a permanent scaffolding of thick silk threads that is strung up between the trees.
Then at sunset, the huddle breaks apart. Individuals disperse along the shared framework and choose a spot to build their own circular orb web, which they use to catch insects. At dawn, they eat the web and follow the communal threads back to the safety of the bivouac.
So, the illusion had a simple explanation. The spiders were suspended in their night-time webs, waiting for insects to become ensnared. The silk was so fine it was almost invisible, so from the ground, the web disappeared. For a few hours, São Thomé das Letras looked less like a quiet Brazilian town and more like a scene from a Tim Burton movie.
