Spiders eat more meat every year than the entire human race. A 2017 study in The Science of Nature put the annual kill of the world's spiders at 400 to 800 million metric tons of prey. Humans eat around 400 million tons of meat and fish a year. Whales take an estimated 280 to 500 million tons. Spiders are in that league, and at the upper end of the estimate they are ahead of everyone. More than 90% of what they catch is insects and springtails. The arithmetic behind that number is the part worth sitting with. All the spiders on earth come to roughly 25 million tons of biomass, a small fraction of what they consume, because each one eats many times its own weight over a year and there are an extraordinary number of them. Grassland and forest floor can support up to 1,000 spiders per square meter. More than 45,000 species have been described, living on every continent except Antarctica. What that adds up to is pest control running continuously, everywhere, at no cost to anyone. A large share of what spiders eat is exactly what would otherwise be eating crops, spreading disease, or getting into a house. The same logic that makes bats worth roughly $23 billion a year to American agriculture applies here, at a scale nobody has fully priced. None of this requires liking them. The overwhelming majority of spiders in North America cannot meaningfully hurt a person, and the one in the corner of a basement is working. Killing a house spider removes something that was eating mosquitoes and silverfish, and replaces it with nothing. A garden with spiders in it is a garden with fewer things eating the garden.