The bacterium that causes anthrax (Bacillus anthracis) depends on viruses to survive. When it’s not ravaging livestock or being used in bioterrorism, the anthrax bacteria spend their lives as dormant underground spores. It weathers these harsh conditions by using genes that it picks up from infecting viruses. This borrowed DNA allows it to grow more quickly, cluster in groups, and even infect a secondary host – the common earthworm. The viruses may kill some of the bacteria they infect, but the survivors are hardier for it.