Read the passage. Then answer the question.
a barn swallow preening
A barn swallow preens, or grooms its
feathers, by coating them in a thin layer
of oil. The oil comes from a small organ
near the swallow's tail, called the preen
gland. The oil from the preen gland
keeps the swallow's feathers strong and
flexible.
The oil is also used by a small arachnid
called a feather mite. The feather mite
lives on the swallow's feathers and eats
some of the oil. But, this type of mite
does not affect the growth or condition of
the swallow's feathers.
Which type of relationship is formed when a feather mite lives on a barn swallow's feathers?
commensal
mutualistic
parasitic