This patient complained of pruritus on his ankle. Of note, he traveled to Costa Rica several weeks prior. The botfly (Dermatobia hominis) is responsible for myiasis. It is common in Central and South America, and will occasionally be seen in the United States without a travel history. The fly lays its eggs on an unsuspecting vector, which transfers the eggs to its host (usually cattle or humans). The eggs hatch fairly rapidly and the larva works its way to the surface. I have a friend who videotaped a larva exiting her friend's navel area….cool! On histology, the larva can be identified by its skeletal muscle, lack of eggs, and characteristic yellow spines.
Separate from the punch biopsy (likely separated during processing), there is a large organism. It has a thick, purple outer layer with widely spaced yellow spines. The interior of the organism shows abundant skeletal muscle.