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Tuesday, September 23, 2014

Snake poop and the adaptive ballast hypothesis

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Alternate title suggested by David SteenWhy snakes might benefit from holding it 

Most people probably spend as little time as possible thinking about poop, especially snake poop. Some animals produce enormous amounts of poop, like dairy cows. Others make lots of little poops - up to 50 a day in small birds.  In contrast, snakes don't poop much at all. In fact, because they eat so infrequently, snakes probably poop the least often of almost any animal. Anyone who has kept a snake as a pet can tell you that a few days after they're fed, most snakes tend to poop once (often in their water bowls, for some annoying reason), and they might poop again within a few more days. Like bird poop, snake poop is made up of two parts - the brown stuff (the fecal fragment, aka the actual poop) and the white stuff (the uric acid fragment, aka the pee, in a solid form). Also like birds, most reptiles use uric acid rather than urea to excrete their excess nitrogen, which helps them conserve water.

A young Racer (Coluber constrictor) that has eaten a
Ring-necked Snake (Diadophis punctatus) nearly 92% its length
You wouldn't think there would be much that's interesting about snake poop, but to a snake biologist everything about snakes is interesting. In 2002, Harvey Lillywhite, Pierre de Delva, and Brice Noonan published a chapter in the book Biology of the Vipers that detailed their studies on snake poop. Their most amazing finding was that some snakes can go for a really, really long time without pooping. As in, over a year. It's not because they're constipated though - these long fecal retention periods have actually evolved for a purpose in snakes. Here's what happens: most snakes eat very large meals, and they eat them all in one piece. That means that when a snake eats a meal, its body mass can more than double all at once, and it can only digest that meal from the outside in, because it hasn't chewed or cut it up into small pieces to increase its surface area. Even for the insane digestive tract of a snake, this is an incredible feat.

And the python's small heart grew two sizes that day
Figure from Riquelme et al. 2011
A well-publicized series of studies by Steve Secor and Jared Diamond on snake digestion is more than fascinating enough to warrant some digression. They revealed that some snakes actually let their digestive tracts atrophy between meals, and rebuild them (and many of their other organs, including their hearts, which double in size) each time they eat. If that sounds strange, remember that some snakes only eat a few times a year, unlike we mammals who must eat every day. In one paper on the subject, the authors used an analogy with driving a car in normal traffic vs. stopping at a railroad crossing. It's fine to keep the engine running during a brief stop, but turning the engine off saves fuel while waiting for a train to pass. By shrinking their organs, snakes are saving energy during the long fasts between meals. The flexibility of their body temperature and fundamental differences in their mitochondria are two of the ways in which snakes are able to endure these extreme fluctuations in their metabolic rate. As their gut size and metabolic rate change, so does their ability to uptake nutrients, which brings us back to the production of poop.

Uromacer oxyrhynchus just can't hold it's poop
Poop is what's left behind after your gut has extracted all the nutrients it can from a meal. The ability of a snake's gut to extract nutrients from its prey can change a lot as the gut itself is rebuilt following a meal. Specifically, it is highest following feeding and tapers off as physiology and morphology return to their pre-feeding states. Normally, once food has been reduced to poop, it doesn't hang around for long. This is true in mammals and birds and in some snakes, including ratsnakes, which normally take about two days between eating and pooping. Even that's relatively long compared with we humans, who are clinically constipated after three days. Other relatively slender or arboreal snakes such as bush and tree vipers (3-7 days) and tree pythons (~6 days) poop fairly regularly, and fecal retention time is at a bird-like minimum of 23 hours in the slender Hispaniolan Pointed-nosed Snake (Uromacer oxyrhynchus). But in other snakes, particularly in heavy-bodied species of henophidians and especially in terrestrial vipers, poop stays in the hindgut for months, even when they are fed often. The maximum values recorded by Lillywhite for boas and pythons fed mice are impressive: 76 days in an Emerald Tree Boa (Corallus caninus), 174 days in a Burmese Python (Python molurus), and 386 days in a Blood Python (P. curtus). For vipers, the figures are just as astounding: 116 days for a Puff Adder (Bitis arietans) and 286 for a Rhinoceros Viper (B. nasicornis) are among the longest, although nothing holds a candle to the heavyweight champion: one Gaboon Viper (B. gabonica) in Lillywhite's dataset that didn't poop for 420 days!

A Burmese Python intestine before (top), two days
after (middle), and 10 days after (bottom) eating.
From Secor 2008
The intestine of a snake can hold a lot of poop. Lillywhite & colleagues measured this by pumping (dead) snake intestines full of saline and found that an average viper hindgut can hold about twice as much total volume as that of a ratsnake. The cumulative mass of the poop stored by the vipers in their study totaled between 5 and 20% of the total body mass of the snakes. In humans, this kind of thing would cause an awful, awful death (some say that's what happened to Elvis). Why did these snakes do this? Lillywhite and colleagues put forth what they called the adaptive ballast hypothesis to explain their observations. When I first heard about the adaptive ballast hypothesis, I actually thought it would be that snakes held onto their poop so that they could use it defensively, in case they needed it to spray onto their would-be assailants during some future predation attempt or capture by a herpetologist. But in fact, it goes something like this:

Poop from this African Rock Python's last meal might help anchor it
as it laboriously swallows this wildebeest
Clearly, being heavy is not advantageous for arboreal snakes, so they poop on a regular basis shortly after eating. In terrestrial snakes, however, a little extra weight can give a snake a distinct advantage in capturing and handling large, potentially dangerous prey. Stored feces contribute an easily-altered component to the body's mass, an inert ballast that, unlike muscle, requires no energy to maintain (so long as the animal is sitting still and doesn't have to drag it around, a perfect fit for the sedentary lifestyle of pythons and vipers - no word yet on fecal retention in the sluggish elephant trunksnakes). This extra mass is concentrated in the posterior of the body, where it presumably increases both the inertia of that region and its friction with the ground. Essentially, the humongous mass of poop could anchor the back end of the snake during a strike or while constricting. Although no one has explicitly tested this idea, it's compelling, because the same evolutionary pressures that caused pythons and vipers to have heavy bodies in the first place could be selecting for these long retention times if they help the snakes more easily obtain food. What's more, the snakes could jettison their ballast quickly if it became a liability, such as following a new meal, before undertaking a long-distance movement, upon becoming pregnant, or prior to hibernation, thereby reducing their body mass by as much as 20% at one go.

In addition to providing ballast, the long time the fecal material spends inside the intestine could potentially increase the absorption of nutrients and water, although it probably doesn't take many months before the snake has got all it can out of its old meals. Uric acid and feces are normally mixed in snakes with short passage times, but in heavy-bodied viperids, boids, and pythons, feces are usually more compact and are more separate from the uric acid.

Few people have looked very deeply into these patterns of defecation (perhaps few would want to), so a lot of questions remain: does more frequent activity induce premature defecation? Do drinking or skin shedding influence defecation patterns? Do these patterns hold up in the field? What other functions might snake poop have? One study showed that captive snakes pooped more quickly after their cages were cleaned, whereas control animals whose cages were merely rearranged did not, which suggests that snakes might be using their feces for marking...something (we really don't know what since they aren't generally thought of as territorial, although they are a whole lot more social than most give them credit for). The mysteries are many.


Thanks to Pedro Rodriguez for allowing the use of his photograph.


Castoe, T. A., Z. J. Jiang, W. Gu, Z. O. Wang, and D. D. Pollock. 2008. Adaptive evolution and functional redesign of core metabolic proteins in snakes. PLoS ONE 3:e2201 <link>

Chiszar, D., S. Wellborn, M. A. Wand, K. M. Scudder, and H. M. Smith. 1980. Investigatory behavior in snakes, II: Cage cleaning and the induction of defecation in snakes. Animal Learning & Behavior 8:505-510 <link>

Cundall, D. 2002. Envenomation strategies, head form, and feeding ecology in vipers. Pages 149-162 in G. W. Schuett, M. Höggren, M. E. Douglas, and H. W. Greene, editors. Biology of the Vipers. Eagle Mountain Publishers, Eagle Mountain, UT <link>

Lillywhite, H. B., P. de Delva, and B. P. Noonan. 2002. Patterns of gut passage time and the chronic retention of fecal mass in viperid snakes. Pages 497-506 in G. W. Schuett, M. Höggren, M. E. Douglas, and H. W. Greene, editors. Biology of the Vipers. Eagle Mountain Publishers, Eagle Mountain, UT <link>

Riquelme, C. A., J. A. Magida, B. C. Harrison, C. E. Wall, T. G. Marr, S. M. Secor, and L. A. Leinwand. 2011. Fatty acids identified in the Burmese Python promote beneficial cardiac growth. Science 334:528-531 <link>

Secor, S. M. and J. Diamond. 1998. A vertebrate model of extreme physiological regulation. Nature 395:659-662 <link>

Secor, S. M. and J. M. Diamond. 2000. Evolution of regulatory responses to feeding in snakes. Physiological and Biochemical Zoology 73:123-141 <link>

Secor, S. M. 2008. Digestive physiology of the Burmese Python: broad regulation of integrated performance. Journal of Experimental Biology 211:3767-3774 <link>

Creative Commons License

Life is Short, but Snakes are Long by Andrew M. Durso is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.


john said...

A random thought entered my mind while reading this most informative post. What if fecal retention plays a role in thermo-regulation in snakes?
On another subject, I always assumed that snakes defecated shortly after cage cleaning because cleaning the snake's cage causes increased activity as the snake is returned to its cage with new scents to explore. And I thought that it was the increased activity that prompted defecation.

Andrew Durso said...

I'm glad you enjoyed the post John. I suppose it's possible that extra mass helps maintain a more stable body temperature - as far as I know, no one has looked at that. Makes sense what you say about the increased activity prompting defecation, but again I don't think anyone has explicitly tested that idea either.

John Scanlon, FCD said...

Biologists who aren't fascinated by poop and pooping must be, oh, I dunno, botanists or something.

I especially like the Dr Seuss reference!

Andrew Durso said...

Thanks John! The Grinch has always been one of my favorites.

MyIttyBittyDarkSide said...

In my experience with the snakes I keep (especially my Eastern Indigo), even if I haven't cleaned their enclosures, the act of taking them out and putting them back in sparks activity. Without fail, the active snake will poop. Some within minutes, some within hours.

Thank you for your information. Its extremely interesting & helpful.

Andrew Durso said...

Interesting observation! Thanks for reading!

Rosie Gall said...

I came across your site whilst trying to identify poop on our deck. I think its from a diamond python (New South Wales, Australia). There are two different deposits-brown obviously fecal bits and hard white calcified bits. I found similar poop in exactly the same location about 4 months ago which is interesting given your comment about territorial marking.

Andrew Durso said...

Very interesting observation. Have you seen diamond pythons in your yard before? Bird poop also has this brown and white part, so it's possible it could be from a bird.

Rosie Gall said...

Thanks Andrew. I think it sould have to be a mighty big bird!
The white bits are like rocks- about an inch x 3/4 of an inch.
Over the last rhree years we have found python skin shed in the yard
(all scrunched up until we stretched it out) and also when cleaning out gutter on roof.

Andrew Durso said...

Cool! That is huge. You guys have some mighty big birds down under, but I suppose you'd know if you had emus or brush turkeys in your yard. Other non-avian reptiles also make poops like these, so you could consider a large monitor lizard, but I see no reason to believe it's not a python if you've found a shed and have no better candidate. I'm jealous :)

Unknown said...

I have a Woma ball python that we just got about nine months ago. She is taken out of her cage often so she is a pretty active snake. She eats once a week at the pet store, but she's only eating about once every 4 to 5 weeks now that we have her. I noticed that her first real defecation happened a couple of days ago and like I said we had her nine-months. She had a very small defecation about a month prior to this one. The defecation that was small a month ago came after we had to move her tank. Even though it was the same tank it was a new location a freshly cleaned tank and new bedding. This kind of leads me to believe the territorial aspect mentioned here. Because I am a new snake owner, I am unsure and worried about her new eating habits. She has gone from once a week, to more than a month in between feedings, as I have stated. Is this normal? She is about 4 yrs old now, and about 4 ft long. She seems very healthy and she is offered food every week at first and now about every 3. She is fed in a separate container as they did for her whole life span. I am not sure if her eating habits have changed because she is mature now or some other reason, or if I should be worried? Thanks for the help in advance :)

Unknown said...

Also, is she more likely to eat now that she has had a normal defecation? (I forgot to ask that, and that was my main question, lol)

Andrew Durso said...

Hi Catherine, I'm sorry about the slow reply. Eating (and pooping) once every 4-5 weeks sounds pretty normal to me, either for a woma or for a ball python. The eating habits of snakes may change with a new environment, with age, or with the seasons.

Unknown said...

HI i rescued a 16'reticulated python that was skin and bones pretty much almost starved to death. i have been feeding her rabbits weekly and she is looking soooo much better now its almost night and day. however she hasn't pooped in two months someone told me that she could be impacted and i was scared however i honestly felt like she was retaining all the food to absorb everything she can since she probably has no idea she is going to eat again due to her previous keeper. i felt relieved when i read that some have help poop over 300 days so this gives me hope. she keeps accepting food every week so i assume its a good sign. anyhow thanks for this post it makes me hopeful that she is indeed retaining all the nutrients to rebuild and be healthy again. she is a 16 year old Gstripe retic and i love her dearly. I currently keep 46 snakes and two of them are rescues.

Andrew Durso said...

Really good to hear Robert. Yes, it's quite amazing how long they can go, and it really messes with the human sense of what's right and wrong. Keep up the good work!

Teresa said...

My Brazilian rainbow boa just pooped, 2 months after his last poop. I’ve had him for about a year and always get worried because he hardly ever poops so I’m glad I found this!

BRBs are semi-arboreal so that doesn’t jibe with the ballast thing, but I wonder if the infrequent pooping has to do with the fact that he hardly ever goes to his warm area (and BRB temps are lower than most reptiles) and he is also pretty inactive and spends the majority of his time buried in his substrate. I actually saw him soaking in his water bowl last night which is pretty normal for BRBs but not him in particular, and he also was hanging out in the warm side of his enclosure for once—I wonder if he instinctively did all that to move things along.

Andrew Durso said...

Great! Glad you found this information useful. Temperature is definitely one of the most important drivers of all physiology for most reptiles.

Unknown said...

Hi. I have a 6 year old Jungle Python who we have had for about two & a half years now. My partner used to have her at his workshop but as he is now working interstate, I have had her at home for 8 or so months now. As she is quite inactive in her enclosure, about once a week I will take her outside on the grass for some exercise. About 3 months ago when she was outside, she done a poo. I had never seen her poo before & wanted to know more about her bowel habits as I think it’s important to know. Ever since her first poo outside, she does not poo in her enclosure anymore. I feed her a large frozen rat every 2-3 weeks. Anywhere from about 5-7 days after her feed, she gets taken outside to see if she would like to go to the toilet. She normally will do quite a decent sized poo, it actually looks like a large dog poo, but other times she will just do a little bit which then I will take her back outside normally about 3-4 days later to do her big poo. I was unsure what the hard, white poos actually were but after reading your article, I now know. Sometimes she will have a bit tiny bit of yellow in with her white poos. I always inspect her as she is pooing just to make sure everything is going normal for her. I just like the idea that she will only pop outside now. I tell everyone I have a toilet trained snake!!

Andrew Durso said...

That is way cool! Thanks for sharing.

Unknown said...

Just thought I’d throw this out there, I had an Atropoides olmec go 115 days (March 18 - July 11) without pooping recently. When she finally did I got 13 fangs out of it, I dig through all my snake poop for fangs and this one was full of treasure!

Andrew Durso said...

Holy cow! That's awesome. I bet that poop looked like a porcupine...