Pine bark mulch attracts subterranean termites—those that live underground. Although the mulch is wood, it is not the mulch's value as a food source that attracts termites: It makes an ideal nesting and tunneling area for them.
Termites observed in a study titled "Termite Survival on Various Types of Mulch" died after 16 weeks of eating only mulch made of pine bark. Those eating pine bark nugget mulch died two weeks earlier than those eating mulch made of shredded pine bark.
Termite colonies constantly send out scouts to tunnel around looking for food sources. Pine bark mulch stays moist longer than surrounding dirt, making it more accommodating for subterranean tunneling termites.
To avoid providing an ideal tunneling area for termites, never place mulch so that it is touching any part of the home. Mulch, flowerbeds and shrubs should be kept several inches away from the house.