How thousands of nature’s longest sperm squeeze into a tiny fruit fly
By bringing mathematics and biology together, researchers at the Simons Foundation’s Flatiron Institute have uncovered the dynamics of how supersize fruit fly sperm behave when packed into a small space.
Simons Foundation
image:
Visual explainer that shows the enormous length of the fruit fly sperm compared to the sperm storage sac: The sac is only one tenth the length of the fruit fly sperm. The fruit fly sperm is 40 times longer than a human sperm.
view moreCredit: Lucy Reading-Ikkanda/Simons Foundation
The supersize sperm of fruit flies swim about their storage cavity with elegant churning choreography, and scientists at the Simons Foundation’s Flatiron Institute have figured out why.
Within the abdomen of the humble fruit fly (Drosophila melanogaster) are some of the longest sperm the animal kingdom has ever known. Uncoiled, the tails of these swimmers stretch around 2,000 microns long. That’s nearly the length of the male fly itself, and 10 times longer than the storage organ that houses sperm by the thousands.
Yet surprisingly, the sperm-filled organ isn’t a chaotic mess. The sperm form orderly flows, undulating like waves. “Each one of them is dragging this massive cargo, and they’re not getting entangled,” says Jasmin Imran Alsous of the Flatiron Institute’s Center for Computational Biology (CCB). “That’s what really blew my mind.” The question became: How could they move around in such tight quarters without getting tangled up in knots?
To find out, Imran Alsous and her collaborators developed mathematical models that could be used to simulate the highly complex biological system. They found that, rather than propelling themselves by creating waves through fluid like human sperm, fruit fly sperm actually push off their brethren to propel themselves forward. When thousands of sperm interact in this manner, the result is a collective churn.
The researchers report this new understanding of how individual fly sperm movements give rise to orderly collective dynamics in a new paper published June 22 in Nature Physics.
The larger ethos behind their work — building collaborations to develop quantitative approaches to reproductive biology — could help scientists answer other fundamental questions in biology, such as how nutrients flow through networks of veins, how organelles self-assemble within cells and how embryos develop.
“This is how you’re going to reach a truly quantitative understanding of biology,” says CCB Director Mike Shelley.
For the full story behind the new work, read our article “Mysteries of Fruit Fly Sperm Untangled by Mathematical Models.”
About the Flatiron Institute (CCB)
The Flatiron Institute is the research division of the Simons Foundation. The institute's mission is to advance scientific research through computational methods, including data analysis, modeling and simulation. The institute's Center for Computational Biology develops new and innovative methods of examining data in the biological sciences whose scale and complexity have historically resisted analysis. The center's mission is to develop modeling tools and theory for understanding biological processes and to create computational frameworks that will enable the analysis of the large, complex data sets being generated by new experimental technologies.
Stylized illustration of sperm tails coiled up and aligned tidily.
Credit
Lucy Reading-Ikkanda/Simons Foundation
Time-lapse of a collection of fruit fly sperm, with red-colored heads and gray-colored tails, showing how they "flow" together, showing the collective dynamics that Jasmin Imran Alsous and colleagues are studying.
Colorized time-lapse of an individual sperm. The sperm uncoils at random like an earthworm in a puddle showing the juxtaposition of single sperm dynamics vs. the collective.
Credit
J Imran Alsous, et al./Flatiron Institute
Journal
Nature Physics
Method of Research
Experimental study
Subject of Research
Cells
Article Title
The physical consequences of sperm gigantism
Article Publication Date
22-Jun-2026
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