Egg-eating snakes

On my trip to Kentucky I had the pleasure of meeting James Krupa, a biologist and natural historian with wide research interests.  One of his specialties is a bizarre group of reptiles:  egg-eating snakes.  Actually, there are two groups: five species of African egg-eaters in the genus Dasypeltis, and the single species of Indian egg-eater, Elachistodon westermanni. These snakes not only can eat eggs, which they swallow whole, but that is all they eat.

Krupa kindly showed me these snakes as well as their skeletons and remnants of the eggs they’d nommed.  As you might expect, they have numerous adaptations for dealing with this difficult food.  First of all, they’re toothless, since teeth would impede the swallowing of eggs.  Here’s a skeleton of one; note that where the teeth usually are, there’s nothing.

Because they’ve evolved toothlessness, they have a problem: how do they defend themselves?  Krupa suggested that selection has acted to make them mimics of other, poisonous snakes.  This is Dasypeltis atra, the montane egg-eating snake, which resembles a mamba. Isn’t it lovely?

They’ve also evolved a threat display that involves squirming around when cornered and rubbing their scales together.  This produces a hissing sound. Here’s a video of a baby Dasypeltis atra showing that behavior:

The eating of an egg by one of these snakes is truly a wonder of nature.  They swallow the thing whole, and it’s often several times larger than their diameter (see video below).  When the egg is some way down the throat, they contract their muscles and move from side to side.  This presses the eggshell against special protrusions on the snake’s vertebrae, which pierce the egg.   This photo of a skeleton shows the egg-piercing protrusions (circled)  that have evolved on some of the vertebrae:

Their tracheas are specially flattened so that they’re not occluded when swallowing an egg. This allows the snake to breathe during the time-consuming process of swallowing.

After they pierce the egg and squeeze out every drop of the contents, they regurgitate the shell.  Here’s Krupa holding the remnants of a large egg that’s been nommed.  Note the neat piercings down the center, where it’s come against the vertebrae:

And a video of the whole remarkable process, which I didn’t see.  I believe this is the Southern brown egg eater, Dasypeltis inornata:

It’s easy to envision the evolution of this ability.  Some snakes, like the rat snake, already eat smaller eggs as part of their diet.  If you lose your teeth, and evolve some protrusions on your spine, you suddenly gain access to a rich source of nutrition unavailable to other snakes.

44 Comments

  1. Posted October 20, 2010 at 6:22 am | Permalink

    Fascinating, but… evolved? Shurely shome mishtake. God created these in a fit of boredom, probably around 2.15 on Wednesday.

  2. Posted October 20, 2010 at 6:26 am | Permalink

    “Some snakes, like the rat snake, already eat smaller eggs as part of their diet.”

    Ah, that was my question, but you answered it at the end. I thought some common North American snakes did eat eggs.

  3. Seth
    Posted October 20, 2010 at 6:29 am | Permalink

    Lovely! Snake dentition and foraging behavior is amazing. See here for a case of snakes evolving asymmetrical dentition to better make use of their snail prey. The whole thing falls apart though if the snail operculum is on the wrong side.

    http://evilutionarybiologist.blogspot.com/2009/06/left-handed-snails-beat-snail-eating.html

    • Dominic
      Posted October 20, 2010 at 6:39 am | Permalink

      Fascinating – & I learnt a new word – operculum!

  4. Insightful Ape
    Posted October 20, 2010 at 6:32 am | Permalink

    Very creepy. No pun intended.
    And of them speak Hebrew?
    Good thing serpents don’t have to worry about cholesterol, heart disease and stroke.

  5. Dominic
    Posted October 20, 2010 at 6:34 am | Permalink

    So they presumably rely on an extended egg-laying period for their prey species, then have a torpid season when birds are not laying, or do they find year round nests & eggs? Do any of them eat reptile eggs as well or do they concentrate on birds?

    • Hempenstein
      Posted October 20, 2010 at 7:23 am | Permalink

      Since it sounds like they’re equatorially distributed, I’ll guess that there’s a pretty dependable supply of nests with eggs more or less year-round.

  6. Robert
    Posted October 20, 2010 at 6:51 am | Permalink

    Thanks. I’ll be using these as my organism of the day to start my intro lectures today and tomorrow. Neat little critters.

  7. Posted October 20, 2010 at 7:20 am | Permalink

    Wow–I think my mouth was hanging open as far as the snake’s:)) That was so cool I watched it twice! You could better say he enveloped that egg than ate it–at least until he crushed it and spat up the shell.
    (Operculum–great word! Thanks Seth!…remember…remember:))

  8. jimvj
    Posted October 20, 2010 at 8:07 am | Permalink

    Sorry if this is a bit OT, but this reminded me of the havoc the brown tree snake (& other snakes) have caused on the bird populations of islands like Guam. They also cause electrical outages by climbing up utility poles & straddling wires.

    Is there a way to control or eradicate these exotic snakes by placing suitably poisoned chicken eggs (or smaller eggs of non-threatened birds)? I’m assuming that bird eggs are not eaten by native predators.

    • Sven DiMilo
      Posted October 20, 2010 at 1:42 pm | Permalink

      Brown treesnakes are not particularly interested in eggs, as I understand it. They’ve eaten all the birds and are now starting on the lizards. Last I heard there was a plan to parachute in poisoned mice.

  9. Posted October 20, 2010 at 8:10 am | Permalink

    What did these snakes live on as vegetarians before the Fall?

    • ambulocetacean
      Posted October 20, 2010 at 9:33 am | Permalink

      They eated froots. I heared teh creation science sez teh snake venoms is for softening froots.

      But if these snakes no has venoms then maybe the other snakes softens up teh froots for them.

      I can has Templeton grant?

  10. Posted October 20, 2010 at 8:29 am | Permalink

    Many moons ago, somebody observed to me that people tend to like snakes and dislike spiders or vice-versa. Even if they didn’t care for either, they usually tend to not like the one and loathe the other. Those who like both usually only get really excited about the one.

    Me? I like snakes. I can appreciate spiders on an intellectual level and as abstract art…but, viscerally, I’d rather not have anything to do with them.

    Anybody else notice a similar pattern?

    Cheers,

    b&

    • Seth
      Posted October 20, 2010 at 8:44 am | Permalink

      I dig both. On the spider side Salticids a.k.a. jumping spiders are my favorites. They have telephoto eyes, and some of them are spectacularly intelligent.

      • TrineBM
        Posted October 20, 2010 at 8:51 am | Permalink

        I like snakes! And I think that I’ve matured a lot in recent years, since I do not per default kill any spider near me anymore. No, some spiders get to cohabitate with me … even though I’m still not very happy about it.
        My son dreams of having a terrarium with an egg-eating snake. “But mom, they don’t even have teeth! Pweeeezzzeee can I have one???? huh? huh???”

        • Kevin
          Posted October 20, 2010 at 3:38 pm | Permalink

          I have a strict rule which all the spiders understand…

          Outside spider = good spider.

          Inside spider = dead spider.

          • Hempenstein
            Posted October 21, 2010 at 8:59 am | Permalink

            I’ve never had a problem with any in-house spider. A couple yrs ago I had a Drosophila infestation in the kitchen from some pears that came in off my tree in the fall. Then I noticed a little spider tunnel by the sink drain. Whenever a fly would get near the opening, he’d spring out and nab it. When the Drosophila invasion eventually subsided, the spider went elsewhere. If you kill spiders, the bug level rises, and then you have more spiders clamoring to get in. The self-limiting approach seems to work well.

    • TheBear
      Posted October 20, 2010 at 9:37 am | Permalink

      I think both snakes and spiders are amazing creatures, and would be hard pressed to give you a hard preference for either.

      More rl-experience with spiders though (and usually the small cute kind). Thought living in scandinavia, the local wasps are more dangerous than either the local spiders or the local snakes (and those I don’t like)

    • Diane G.
      Posted October 20, 2010 at 1:03 pm | Permalink

      I like both, tho I seem to have an inherent arachnophobia that sometimes crops up when spiders appear unexpectedly (which is their forte). Snakes, tho equally “sneaky,” just don’t elicit that pit-o’-the-stomach queasiness for me. I do have 8 tarantulas that fascinate me–the oldest is 9 years old & I’ve raised her since she was a very small spiderling…this familiarity has helped a ton with the phobia thingy…

  11. Josh Slocum
    Posted October 20, 2010 at 9:21 am | Permalink

    Very, very cool. Something I wouldn’t have said 10 years ago, when I was still suffering from a Shuddering Terror at the very sight of a snake. Making friends with a herpetologist at a local college helped – he let showed me his collection, and encouraged me to hold some of the friendlier specimens. After the initial heebie-jeebies, I found they really are quite beautiful, both in their appearance, and in their fascinating locomotion.

    Legless lizards, however, are another story. On that same trip to the herp lab, the little bastard decided he was cold, and started flipping his stiff body from side to side so as to wriggle up the sleeve of my shirt. Stark. Staring. Horror. Oh, sweet jesus, get that thing out of my clothes.

  12. M31
    Posted October 20, 2010 at 9:35 am | Permalink

    Fascinating. Do they have a problem if the chick in the egg is well developed? It seems like they crack the shell and then squeeze the liquid out.

    • Diane G.
      Posted October 20, 2010 at 1:09 pm | Permalink

      Very good question. In addition to the not-flowing-out-of-the-shell problem, an advanced chick embryo would have bone & feather that might not suit the snake either.

      I’d expect the snake can somehow ‘judge’ the development of the egg…amount of sloshiness, that sort of thing…

      In the vid, I loved the way the snake stood the egg on end–easier to corral it that way, rather than having it slide along on its long axis…

      • Diane G.
        Posted October 20, 2010 at 1:14 pm | Permalink

        Google is my friend…from Wikipedia:

        They are agile climbers, and have a keen sense of smell to tell whether an egg is not rotten or too far developed to be comfortable to eat.

  13. ambulocetacean
    Posted October 20, 2010 at 9:39 am | Permalink

    Is this really that uncommon? I thought a lot of snakes were egg suckers.

    When I was a kid I heard a story about snakes getting into chicken pens, swallowing eggs and then getting stuck in the chicken wire because the egg wouldn’t fit through the mesh. Then the guy who owned the chickens would cut off the snakes’ heads with a shovel.

    Might not be true, I guess.

    • Marella
      Posted October 20, 2010 at 4:47 pm | Permalink

      I heard the same story but it was entire chickens that got swallowed, not just eggs. Mind you this story came from Queensland where the snakes are often pythons!

  14. CSN
    Posted October 20, 2010 at 11:33 am | Permalink

    How do the spikes puncture the egg without also puncturing their own digestive tract?

    • Sven DiMilo
      Posted October 20, 2010 at 1:44 pm | Permalink

      The specialized vertebral spines actually do protrude through the esophagus wall.

      • Posted October 20, 2010 at 5:16 pm | Permalink

        Thanks! I’ve always wondered about that. Do you know if the North American species, like the rat snakes, simply rely on muscular contraction to crush the egg? Which would be an impressive feat, really…

  15. Posted October 20, 2010 at 11:40 am | Permalink

    wow very neat.

  16. Posted October 20, 2010 at 12:01 pm | Permalink

    “If you lose your teeth, and evolve some protrusions on your spine, you suddenly gain access to a rich source of nutrition unavailable to other snakes.”

    Suddenly? Paging Dr Behe, paging Dr Behe.

    Hahahaha

    • Josh Slocum
      Posted October 20, 2010 at 2:29 pm | Permalink

      “Thank you for calling the Department of Irreducible Complexity. Your call is very important to us. Unfortunately, Dr. Behe is busy defending himself against other interlocutors. Your expected wait-time is forever.”

  17. prasad
    Posted October 20, 2010 at 5:26 pm | Permalink

    Is there a reason they couldn’t simply break the egg and get at the contents? Why with the swallowing whole and becoming temporarily defenseless?

    • whyevolutionistrue
      Posted October 20, 2010 at 5:29 pm | Permalink

      How would a snake break an egg? Those shells are pretty smooth and tough!

      • Sven DiMIlo
        Posted October 20, 2010 at 5:58 pm | Permalink

        How would a snake break an egg?

        ball-peen hammer?

      • Hempenstein
        Posted October 21, 2010 at 8:49 am | Permalink

        Occurs to me that either use of DDT was not widespread in the egg-eaters habitats, or the birds whose eggs they eat are not particularly susceptible to the shell-thinning effects. Otherwise, the shells should have become so thin that they’d be broken as the snake started to get its mouth around one, pushing them toward extinction.

    • Posted October 20, 2010 at 10:30 pm | Permalink

      I was wondering the same thing – especially doing it the hard way, taking the egg in side-on. With teeth or fangs they could pierce the shell and just suck the contents out. Maybe the shells are thicker than we’re used to (in defence against snakes?) and maybe they worked up from smaller more swallowable eggs.

      Teach not thy parent’s mother to extract
      The juices of the infant bird by suction;
      That good old lady can the feat enact
      quite irrespective of thy kind instruction.

  18. Posted October 20, 2010 at 5:27 pm | Permalink

    Great post, but then again, I’m a snake lover. The video of the egg-eating snake is especially impressive. You made me throw up my own snake post that has been stewing for the past couple of days, but I don’t have cool video.

    The aggressive display is interesting, especially for what it lacked. Even non-venomous snakes fake strikes and open-mouthed attacks, so it seems strange that the lack of teeth would cause this to stop. I was going to speculate about the potential lack of other dangerous, striking snakes for predators to be familiar with, but mimicking a mamba puts that idea to rest. Curious.

    I also noticed no tail vibrating, which is a common warning display in North American snakes at least. Does anyone know if this is common in other areas? It seems to work very well, even without something to rattle with or against.

    Very cool, thanks!

    • Diane G.
      Posted October 21, 2010 at 12:48 am | Permalink

      Even non-venomous snakes fake strikes and open-mouthed attacks, so it seems strange that the lack of teeth would cause this to stop.

      Maybe it’s the fangs displayed in such activities that makes them successful fakes, then?

      I, too, was kinda wondering just how that aggressive display was very, well, aggressive. Except that watching the “sinuousity” was pretty mesmerizing!

      I wonder if it could have something to do with keeping a potential predator unsure of just where the head-end of the snake is, as I think snake predators often go for that end…Which would make it more defensive than aggressive, of course…

  19. Jan-Cor Jacobs
    Posted October 26, 2010 at 4:19 am | Permalink

    I kept some of these snakes some years ago (and even bred them). They are real fun to keep and watching them eating and spitting out the egg scales is really fascinating!

  20. Posted June 18, 2012 at 12:05 pm | Permalink

    I’ve captured a rat snake in my hen house. Seems to have an egg half way down his length. A ceramic egg is missing. If he swallowed it, can it pass through its system or is the snake doomed? Usually, I tranport these snakes a good ways and release them, but if this one is going to suffer, I will put him down.

    • Diane G.
      Posted June 18, 2012 at 7:36 pm | Permalink

      June, what a fascinating, if bizarre, predicament. Poor snake. Interesting that the snake would not have noticed the “artificialness” of the egg-like object, but then I guess they didn’t evolve with ceramic imitations…

      I hope an actual expert responds, but since this is an old thread, you may need to find another information source to consult.

      My first thought is that the more distal reaches of its GI tract would probably not be capable of such extreme expansion…

      (But then I never thought I could have a baby, either; until push came to shove, as it were…Sorry, couldn’t resist.)

      • whyevolutionistrue
        Posted June 18, 2012 at 7:46 pm | Permalink

        We have an expert in hand, and June has been contacted. If she can get the snake to an animal surgeon, a quick and efficacious fix is likely

        • Diane G.
          Posted June 18, 2012 at 7:58 pm | Permalink

          Glad to hear that!

          (And also to know I’m not the only chicken keeper with snake-empathy.)


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