The intromission of the male's long, flexible, threadlike phallus into the female's similarly long, thin, S-shaped vagina in tephritid flies is mechanically challenging. The male of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann, 1824), folds the basal portion of his phallus back on itself, inserts the folded portion into the female, and then gradually unfolds his phallus inside her vagina. The site of the fold in the phallus gradually moves distally, deeper into the female, dragging the distal portion of the phallus into her vagina. At the same time, the male pulls the tip of the female's ovipositor distally with his surstyli, straightening her vagina. The male uses his phallapodeme and asymmetrical syntergosternite to periodically clamp and release portions of his phallus that have not yet entered the female. Once the entire distal portion of the male's phallus is inside the female, he unfolds it and then moves its distal tip even deeper, reaching the inner end of her copulatory bursa. Straightening movements of the phallus due to increases in fluid pressure probably supply at least part of the force that drives the phallus into the female.