A host is an organism which provides shelter for parasites. Parasites will live on the animal and may lay their eggs on them.
Buff ermine moth caterpillar, a polyphagous micropredator
Mycorrhiza, a mutualistic interaction between a plant's roots and a fungus
Cleaning symbiosis: a Hawaiian cleaner wrasse with its client, a yellowtail wrasse
Nurse shark playing host to commensal remoras, which gain a free ride and which may serve as cleaners