You Can Now Mail Frozen Mouse Sperm On A Postcard (OK, Scientists Can)


Dr. Katie Spalding

Katie has a PhD in maths, specializing in the intersection of dynamical systems and number theory.

Freelance Writer


The postcard in question. Image Credit: Daiyu Ito, University of Yamanashi

It turns out scientists have been mailing each other postcards covered in mouse sperm.

It sounds bananas, but this is actually big news. Transporting samples between labs is important, but risky – and so this development, published today in the journal iScience, is a big win for the scientists involved.


Previously, researchers were limited to expensive and difficult methods of sperm storage and transportation. Now, it’s as easy as mailing a letter.

“The postcard strategy was easier and cheaper compared to any other method,” explained first author Daiyu Ito in a statement.

“We think the sperm never expected that the day would come when they would be in the mailbox.”

This postcard technique was so successful that baby mice were successfully born using the samples. That’s really good news, meaning that lots of sperm can be transported without losing quality.


In fact, the scientists have already created what they call a “sperm book” made entirely of pages of… well, the clue is in the name.

Sperm. It's a book made of sperm. Image Credit: Daiyu Ito, University of Yamanashi

It's difficult to overstate how important mouse sperm is in science. The team was previously responsible for sending what is diplomatically described as “large volumes of mouse sperm” to the International Space Station to investigate the effects of space radiation on mouse babies. The same techniques are also used in infertility treatment development, livestock production, maintenance of strains of genetically modified mammals, and endangered species conservation.

The problem was, most of those “large volumes” never made it to space. They had to be stored in bulky, fragile glass capsules. On top of that, they had to be transported with cushioning to prevent breakages and maintain viability. Only a small amount ended up in orbit.

That’s why the team decided to start looking for alternative methods – specifically, space-saving ones. They tested six different materials that might make it possible to store and transport samples in flat sheets: traditional Japanese paper called washi, wrap, vinyl sheet, weighing paper, filter paper, and oblate. The last two were quickly dismissed as sperm could not be retrieved, leaving just four choices – of those four, weighing paper proved the winner.


“When I developed this method for preserving mouse sperm by freeze-drying it on a sheet, I thought that it should be able to be mailed on a postcard,” said Ito, “and so when offspring were actually born after being mailed, I was very impressed.”

Having figured out how to mail the sperm without losing potency, there was just one thing left to do: try it for real.

The team attached plastic sheets containing sample-splattered weighing paper to postcards and sent them tens of miles through the post with no other protection. One scientist even sent another a “Happy New Year” postcard with a gift of mouse sperm attached, which goes to show that it truly does take all sorts to make a world.

Baby mice doo doo doo doo doo doo. Image Credit: Daiyu Ito, University of Yamanashi

Once the technique has been perfected, the team thinks it might be a game-changer for their field. They even plan to find a way to bring the freeze-dried sperm “back to life” in future, so that they can fertilize an egg as normal after transport.


“Genetic resources are an asset to humanity’s future. Even though many genetic traits are not needed for survival, depending on the environmental context, it is necessary to preserve them.” explained senior author Teruhiko Wakayama.

“The plastic sheet preservation method in this study will be the most suitable method for the safe preservation of a large amount of valuable genetic resources because of the resistance to breakage and less space required for storage.”

The postcard, with mouse sperm attached. A marvel of modern science. Image Credit: Daiyu Ito, University of Yamanashi



Receive our biggest science stories to your inbox weekly!


  • tag
  • genetics,

  • sperm,

  • mice,

  • semen,

  • mail,

  • weird and wonderful