Mulch provides many benefite in the landscape. It helps prevent the loss of water from soil by evaporation and can improve the absorption of water into the soil. Mulch can supress weeds; moderate soil temperature; and reduce erosion. The University of Florida recommends organic mulches since they add organic matter to our infertile soil as they decompose. You do not need to remove old organic mulch when you apply new - the old will just decay and add organic matter back to the soil.
The question of termites in mulch comes up quite often. A University of Florida/IFAS research study conducted using Cypress, Eucalyptus, Melaleuca, Pine bark, Pine straw and utility mulch showed that termites fed on all of the mulches. However, Melaleuca mulch was the most resistant to termite feeding.
In Florida, termites are already in our soil. Mulch increases the ability of termites to survive where they are already extablished by keeping the soil moist and temperatures moderate. Mulch applied at greater than 4 to 6 inches thick up to the foundation can also provide a bridge over the treated perimeter of a house, allowing termites to walk over from landscape to house and avoid contact with soil treated with termiticides. It is best to keep at least a 12 inch area adjacent to the foundation free of mulch or other ground covers. Mulch is useful in keeping mud from splashing up against a house, so, it is recommended that no more than a thin layer (about one inch) of mulch be placed within 12 inches of the foundation to allow the soil beneath to naturally dry if you need it. Drying out is the termite's wost enemy. You will also want to avoid watering next to foundation walls.
Termites are everywhere in the Florida soil environment, so the best defense is to keep termite protections up to date with soil treatments and/or bait systems.
You can access additional UF/IFAS Extension information about termites at: http://edis.ifas.ufl.edu/topic_termites