Science Questions

How fast do sperm swim and how do they find the egg?

Sun, 8th Nov 2009

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Lisa Rankin & Science Copperfield asked:

How fast do sperm swim? And: How do they actually track down an egg? They’re doing the equivalent of flying from Earth to the Moon, and they’re blind. And they’ve got no rocket to do it in. So how do they know where to go?”


Chris - Well the answer is about 5 mm per minute, and it’s in fact, five body lengths of the sperm per second.  So if you scaled them up, if those were the size of a salmon, that would be the equivalent of the salmon swimming along at 500 miles an hour, or a whale doing 15,000 miles an hour. So the sperm are pretty snappy. They get to the egg pretty fast, certainly within a day or so.

How do they find it? They recognize it by two means. One is a thermal gradient.  They follow temperature so they know that the body gets warmer the further in they go. So they follow the thermal gradient.  And then the second is that the egg oozes out various attractive molecules, in the same way that various inflammatory things attract the immune system in. This pulls the sperm towards the egg because they follow their noses, quite literally. 


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Lissa Rankin asked the Naked Scientists: I am writing a book "What's Up Down There? Questions You'd Only Ask Your Gynaecologist if she was your best friend" (St. Martin's Press, 2010). One of the questions submitted was "How fast do sperm swim?"  Your site lists 3 mm/hr as the speed. Do you have a source for that? I'd love help finding the answer! Thank you. Lissa Rankin, MD What do you think? Lissa Rankin, Thu, 29th Oct 2009

It depends whether you are in the swimming pool or in bed at the crucial moment. FuzzyUK, Fri, 30th Oct 2009

Here's an evidence-based answer from our own site:

- Having looked at a range of sources, and a range of animals, the consensus would appear to be up to 5mm per minute (not per hour - I'm not sure where that came from).

Chris chris, Sun, 1st Nov 2009

Sperm do not "quite literally" "follow their noses". They do not have noses. Such antrhopomorphism is part of why the medical profession failed to understand fertility for so long. Also, they do not "find the egg" on their own. Cillia within the fallopian tubes and on the uterine walls pull the sperm toward the egg. It is male chauvinism which renders the inaccurate picture of "mighty sperm swims toward passive egg." That picture is scientifically false and the product of sexism. Devin, Sat, 23rd Jan 2010

I would like to correct the scaling factor that he offers. If a salmon is 50 cm long and he is traveling at five body lengths per second, then that scales up to 9km/h or 5.6mph. Actually, body lengths per second is near universal factor that is constant with body size. As you can see that holds for sperm too. Though this may vary up to an order of magnitude. Jesse W, Wed, 10th Mar 2010

This is very, very old information. Sperm are not capable of locating or recognizing an egg - the egg finds the sperm and chooses one to pull in. Lynne, Thu, 25th Apr 2013

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