The answer to 'what causes ticks' is that ticks are parasitic arachnids that feed on the blood of animals, including humans. Ticks live in grassy, wooded, or brushy areas and wait on vegetation to latch onto a passing host. They are attracted to body heat, carbon dioxide, and other cues that indicate the presence of a potential host.
Ticks can transmit a variety of diseases, including Lyme disease, Rocky Mountain spotted fever, and ehrlichiosis, so it's important to take steps to prevent tick bites and remove ticks promptly if found on the body.