The following is a good article on mulch and termites from the University of Maryland.
Like daffodils and dogwoods, fresh mulch is a harbinger of Spring. Whether it's traditional favorites like shredded hardwood and pine bark or specialty products like pine straw and cedar bark, gardeners and landscapers depend on organic mulches to conserve water, reduce weeds, and give gardens a tidy, orderly appearance. Subterranean termites are notorious for tunneling into wood items that are in direct contact with the soil, such as planters, fences, and trellises, and gaining access to homes via these exterior fixtures. Homeowners, mindful of this well-earned reputation, often question whether wood and bark mulches can attract and support foraging termites.
Field research at the University of Maryland, College Park, indicates that organic mulches do not attract termites to the underlying soil, nor will the termites consume mulches in any great quantity. Termites have been observed within newly purchased bags of moist mulch, as well as bags that had been allowed to sit undisturbed for a while. The warm, wet environment of these full bags is ideal for the termites, but such conditions do not exist when the mulch is applied to its recommended depth of 3-4 inches. However, foraging termites can travel within the mulch layer and could theoretically use the mulch as a bridge up over a termiticide treatment around a foundation and into a home. For this reason, it is recommended that a band of bare soil be left around foundations. Surprisingly, even pea gravel perimeters should be avoided. Termites have been shown to feed more actively at resources beneath inorganic gravel mulches, presumably because gravel and stone mulches create a cool, moist, “shadow” underground where the insects can take refuge during the heat of summer.
Reprinted from "Landscape Mulches and Subterranean Termites" by Catherine Long, Graduate Student, University of Maryland, College Park