Final answer:
Adult worms are found in locations that vary by species, including human body tissues for parasitic species and soil or freshwater environments for free-living species.
Step-by-step explanation:
Adult worms can be found in various environments depending on their species. Parasitic worms, such as hookworms (Necator americanus and Ancylostoma duodenale), usually reside in the mesenteric venules of the bowel or rectum, whereas others such as the roundworms (Ascaris species) can migrate through the body and eventually reside in the small intestine. Free-living worms like earthworms often inhabit soil where they play a crucial role in recycling organic matter and aerating the soil. Similarly, Strongyloides stercoralis can live in soil and can switch between free-living and parasitic life cycles. The location of adult worms is therefore highly dependent on the species and can include the human body for parasitic worms, or ecosystems such as soil and freshwater for free-living worms. It's also notable that some marine worms are part of the annelid phylum and can be found in aquatic environments.