How do ticks live solely on blood? A study presented in Current Biology (May 31, 2018) has elucidated the crucial role played by symbiotic bacteria that synthesize B vitamins. These nutrients are scarcely found in the blood ticks ingest but are essential to their life cycle. Thus ticks cannot survive to adulthood or reproduce without their bacterial symbionts. The study conducted by CNRS and CIRAD researchers has also shown that the bacteria inherited their B vitamin synthesis pathways from a pathogenic ancestor whose genome underwent gradual degradation.