Physics: How giant fruit fly sperm prevent tail tangling (Nature Physics)
23 June 2026
Giant sperm produced by male fruit flies organise into a densely aligned, highly dynamic living material inside the body, preventing thousands of the cells from knotting or tangling in tight spaces, according to research published in Nature Physics. The findings suggest that collective physical interactions between sperm allow them to remain mobile.
Some animals produce sperm that are exceptionally long relative to their body size. An adult male fruit fly (Drosophila melanogaster) is roughly two milimetres long — about the size of a sesame seed. However, individual fruit fly sperm are roughly the same length at the male itself, with the flagellum (tail) accounting for most of this size. Thousands of these sperm are stored within tightly confined spaces within both the male and female reproductive systems, including the seminal vesicle — the male organ that stores sperm before mating — which measures approximately two hundred micrometres in size. Although the evolutionary reasons for such extreme sperm size have been widely studied, less is known about the physical challenge of packing and storing these long, active cells.
Michael Shelley and colleagues studied how fruit fly sperm are organised and move inside the seminal vesicle. Using high-resolution three-dimensional electron microscopy and live fluorescence imaging, they found that sperm are densely packed and align with one another over distances of tens of micrometres. Rather than staying still, the packed sperm produce collective flows that span the entire organ and persist for hours. Although isolated fruit fly sperm move very weakly, individual sperm within the dense assembly were able to travel rapidly by sliding past neighbouring sperm along shared alignment directions.
Through modelling, the authors suggest that these sperm move by making small bending waves along their tails, pushing against nearby tails that are moving in the opposite direction. The authors suggest that these forces help to keep the relatively long tails of the sperm from getting tangled in both male and female reproductive organs.
- Article
- Published: 22 June 2026
Imran Alsous, J., Chakrabarti, B., Palmer, B. et al. The physical consequences of sperm gigantism. Nat. Phys. (2026). https://doi.org/10.1038/s41567-026-03305-4
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