Tipuana Spittle Bug / Rain-tree Bug

Ptyelus grossus is a Hemipteran spittlebug in the family Cercopidae. Occurring from Southern Africa through to West Africa, the species is gregarious in its larval and nymph stages, feeding on a variety of plants and producing protective nests of acrid foam from the plant's sap. Excreted in large quantities, the foam drips incessantly causing wet patches on the soil below.
Adults have slate-grey wings, each wing with two white and yellow patches near the outer margin. The head is white, rounded with large dark eyes and small black and yellow marks on the forehead. (From Wikipedia)