Female Boa constrictor reproduces without help from males


There is, perhaps, nothing terribly shocking about a female snake, placed in an enclosure with four male snakes, giving birth to two litters of baby snakes.

But what if those babies carry only their mother's genetic material?

Parthenogenesis—breeding without the, you know, breeding—has been documented in only a small handful of vertebrate species, but it does happen. However, usually, it takes the complete absence of males to get the vertebrate ladies going all virgin birthy. These baby boa constrictors, on the other hand, had plenty of potential fathers. But genetic tests have shown that none of the available male snakes is the dad. In addition, the babies are all female. All carry a rare caramel coloration. And all have a very weird mix of sex chromosomes.

In place of X and Y, snakes and many other reptiles have Z and W chromosomes. In all snakes, ZZ produces males and ZW produces females.

Bizarrely, all the snakes in these litters were WW.

This was further proof that the snakes inherited all their genetic material from their mother, as only females carry the W chromosome. "Essentially they are half clones of their mother," says Dr Booth. That is because the baby snakes have inherited two copies of one half of their mother's chromosomes, including one W chromosome.

You know the drill—I, for one, welcome our new female snake-Jesus overlords.

Biology Letters: Evidence for viable, non-clonal but fatherless Boa constrictors (And you can read the full text of the article for free! Also rare!)

BBC: Snake gives 'virgin birth' to extraordinary babies

Via Peter Kobel

Image: Wikipedia user DestructiveEyes, via CC


  1. Supposedly it did happen to one human done 2000 years ago lending credence to the “V” theory of religion. Damn tricky those alien reptiles. Damn tricky.

  2. Boa Constrictors are an invasive species in Florida. The pythons are getting more press, but the boas are there, too. I’m wondering how much this capability contributed to that.

  3. I believe that most species only do this in extremis, i.e. it isn’t a very evolutionarily-sensible thing to do on a regular basis.

    1. Not true! Few species rely exclusively on parthenogenesis, but it’s still common. A common pattern in animals like insects and crustaceans is to use it to spread quickly in the spring, and then start shuffling genes once resources are more limited.

      1. Sorry, Anon (#13), you’re right I should have said ‘most higher animal species’ or something similar.

  4. Thanks for getting Shriekback looping in my head….

    Priests and cannibals, prehistoric animals
    Everybody happy as the dead come home
    Big Black Nemesis, parthenogenesis
    No one move a muscle as the dead come home

  5. They’re not female snake-Jesus overlords, they’re female snake-Mary overlords. Just saying . . .

  6. Thanks for the Shriekback reference! Any song that uses the word “parthenogenesis” is OK by me!

  7. Wow, that’s amazing. I want to have my own babies. Are there laws about carrying your own clone?

  8. Reminds me of the War Games quote:
    Mr. Liggett: Now there seems to be a lot of confusion on this next question: asexual reproduction. Could someone tell me please who first suggested the idea of reproduction without sex?
    David Lightman: Umm.. your wife?

  9. Female Boa constrictor reproduces without help from males, because all she needs is Chuck Norris’ glare to fill her snake uterus to the brim with babies.

  10. It’s already been used by Sheri S. Tepper in her novel Gibbon’s Decline and Fall (1996). The whiptail lizard on the cover is a tip-off – there are a number of species in that family that are parthenogenic, including some in Tepper’s home state of New Mexico.

    Interesting that these baby boas were all females, because it’s my understanding that turkeys produced by parthenogenesis have always been males (ZZ). It will be interesting to see if these boa girls grow up to be parthenogenic like their mama.

  11. They are technically /not/ females, since ‘female’ in this species is defined as ‘ZW’ sex chromosomes. They have female physiognomy, and can likely sexually produce female offspring(and “uber”-female offspring), but they’re an entire other gender (“uber”-female – ?).

    And hypothetically, if the other chromosome in the mother was the one that half-cloned, she could produce males from the parthenogenesis.

    Interestingly, modern science has shown that it’s im-freakin-possible for a human female (XX) to parthenogenetically fertilise (and thus eventually give birth to) a human male (XY), as human females lack Y chromosomes, and 47XXY, 47XYY, and 48XXYY individuals develop as physically male.

    There is still the possibility of true hermaphroditism allowing for such an event, however — in which case technically the resultant offspring’s mother is also his/her sister as well.

    Insert joke here.

  12. And of course it’s just a coincidence that both of the snake sex chromosomes look like little snakes..?!

  13. Note ALL the Royal Society’s pubs are free until the end of the month only (“to celebrate Open Access Week and the 350th Anniversary of the Royal Society”).

    So get in there while you can…

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