A 65-year old man presented with skin lesions on his chest and left arm and shoulder six weeks after i returning from a cacation in Belize at the beach in the fain forest. The lesions occasionally stung, drained a dark exudates, and enlarged despite two weeks of treatment with cephalexin. The patient had no constitutional symptoms. Physical examination reverled five nodules of varying sizes with surrounding erythema and a central pore through which a single, moving larva was observed. This condition is caused by -