Ask Mr. Smarty Plants

Your description does sound like one of the pine sawflies such as Neodiprion taedae linearis (loblolly pine sawfly) or Neodiprion lecontei (redheaded red pine sawfly).  Indeed, the Texas A&M AgriLife Extension issued a Sawfly Alert on April 27, 2011. Here is an article, Pine Sawflies, from the Texas A&M AgriLife Extension and here is information from the U. S. Forest Service and from Ohio State University Extension about the life cycle, damage to trees and control measures for N. lecontei. The good news is that the U. S. Forest Service says that southern pines—this includes Pinus taeda (Loblolly pine)—can survive complete defoliation.  The April 2009 article, Pine sawfly in northeast Texas, from Texas A&M AgriLife Extension says that pines that are defoliated usually recover.  Both the U. S. Forest Service and Ohio State University Extension offer suggestions for biological and mechanical control measures as well as chemical treatments.  You may be able to use mechanical means to remove the larvae; but since your infestation sounds very heavy, you might want to consider using chemical means to control them.  The Texas A&M AgriLife Extension articles above suggest effective pesticides and "Insect and Mite Control on Woody Ornamentals and Herbaceous Perennials" from Ohio State University Extension has general information on chemical as well as other treatments.