Fruit Fly Sperm Pack Into 200-μm Organs, Driving Fast Collective Flows

3 articles · Updated · Nature.com · Jun 22

Thousands of Drosophila melanogaster sperm—each a couple of millimetres long—were found densely packed and highly aligned inside seminal vesicles only about 200 μm across.
Live imaging showed the packed sperm behave like an active material, generating system-wide flows with persistent topological defects while individual sperm move much faster along shared director lines than the bulk material.
The study says isolated sperm are weakly motile, but in dense groups they advance by reptation-like motion—bending internally and pushing against counterpropagating neighboring flagella rather than swimming through fluid.
Experiments and continuum simulations indicate those active stresses keep the giant sperm largely unentangled in both male storage organs and the female seminal receptacle, where about 80% of sperm are stored after mating.
The findings frame giant fruit fly sperm as a physiologically relevant active-matter system and help explain how extreme sperm length can function inside tiny reproductive organs.