The insect that you have described is called the Spittlebug because immature Spittlebugs cover themselves with a mass of frothy foam. They are often found in Centipedegrass lawns. Every lawn has a few of them. When their population gets too high their feeding activity can cause the grass blades to develop a yellow-white streak, purple-red discoloration and browning. If you have a Spittlebug infestation they should be controlled. We can sell you effective chemical controls that you can apply yourself or make arrangements for our Spray division  to treat your lawn for these pests. Click here to see a video on Spittlebugs