Commensalism is a relationship between two organisms of different species, where one benefits but the other neither gains or loses.
Commensalisms vary in strength and duration from long lived symbioses to brief interactions. They can be described by the following types:
Phoresy - Where one animal attaches to another for transportation only, for example mites on insects.
Inquilinism - Where one organism uses a second organism for housing, for example epiphytic plants which grow on trees or birds that live in tree holes.
Metabiosis - After the death of the first organism, the second organism uses something the first created, for example the hermit crab uses gastropod shells to protect their bodies.