Monday, January 31, 2011

Cottonmouth Myths II: Cottonmouth Breeding Balls


Cottonmouths, Agkistrodon piscivorus, are so feared and misunderstood that perhaps the most terrifying thing the average citizen can imagine is these snakes in the process of making even more Cottonmouths.  I would guess it is a combination of fear, rural folklore, and maybe just the fact that Cottonmouth biology is not often brought up in school, but there is a lot of inaccurate information about how these vipers reproduce.  One tale I have heard from time to time is that of the casual fisherman or boater coming across a giant, swirling, tumultuous mess of snakes: a Cottonmouth breeding ball.

A snake breeding ball occurs when there are many male snakes competing over a single (or a few) female snakes.  Wrestling each other for the first opportunity to mate, a breeding ball can be a spectacular sight.  Although there are a number of snake species that are known to engage in this interesting behavior, Cottonmouths aren’t one of them.

Successfully reproducing is one of (if not the most) important activities an animal can accomplish.  This is, after all, the way an individual is assured that their genes may pass on to the next generation.  What kind of species is not driven to reproduce at every opportunity? The extinct kind.


For females of many species, once they are pregnant they are unable to reproduce again for a relatively long time.  This means that when there is a ready, willing, and able female in the area, many males are likely to have their interest piqued.  And if necessary, these males are going to compete against each other strongly for the first opportunity to mate.

Male watersnakes (of the genus Nerodia, for example) may detect a female ready to breed by picking up on her pheromone trail.  If there are many males in the swamp, they may converge on the female at the same time.  There is a huge incentive for being the first male to breed, not only does the male secure a good chance his sperm will fertilize the female’s eggs, but male watersnakes of some species are known to deposit a plug in a female’s cloaca that temporarily prohibits other males from inserting their hemipenes (a male snake’s reproductive organs).  So, with this in mind, the males writhe all over each other (and the female) attempting to be the first to maneuver into position, resulting in a snake breeding ball.

            There are other ways for males to compete for females in the animal kingdom.  One method is by defending a territory from other males, securing the right to breed with nearby females.  Another technique is to impress a female with elaborate displays.  But for male Cottonmouths, the way they secure breeding rights to a female is one that may be familiar to anyone that has spent a lot of late nights in the local bar.  That is to say, when two male Cottonmouths have their eye on the same female, they will simply fight over her.

Cottonmouth combat is probably similar to that seen among other vipers, such as rattlesnakes, wherein the males engage in a ritual combat, raising the front third of their body in the air and becoming intertwined with each other as they attempt to wrestle each other to the ground.  Eventually, one will be determined as stronger, and the victor will proceed to court the female while the loser flees. 

            Unfortunately, we don’t know much else about the behavior surrounding Cottonmouth courtship.  But, it is likely that the winner of the combat has the best chance of mating with the female.

            So, how did the Cottonmouth breeding ball tale start?  I would venture a guess and say that this aquatic viper has simply been once again struck by a case of mistaken identity.  I don’t think it is a stretch to imagine a breeding ball of watersnakes being misidentified as Cottonmouths in the muddy twilight of an isolated swamp.  Watch your step.



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This isn't the first time I've written about Cottonmouths.  For a discussion of Cottonmouths allegedly dropping into boats, click here.

I wrote about how these snakes are quick to show up when a lot of toads (= food) appear here.  I've also written about accompanying Cottonmouth researchers as they wade through swamps to catch snakes in the spring as the reptiles try to take advantage of the new warmth and at night in the summer as the venomous snakes swam around me.  Finally, I provide some tips on recognizing Cottonmouths from non-venomous watersnakes here.

First and third Cottonmouth pictures provided courtesy of Fingerprince Prints.

Much of what I write is based on my experience in the field, however I also rely on the research of others, citations of some relevant scientific articles are below.

Herrington, R.E. (1989). Reproductive biology of the brown water snake, Nerodia taxispilota, in central Georgia. Brimleyana, 15, 103-110

ALDRIDGE, R., BUFALINO, A., & REEVES, A. (2005). Pheromone Communication in the Watersnake, Nerodia sipedon: A Mechanistic Difference Between Semi-aquatic and Terrestrial Species The American Midland Naturalist, 154 (2), 412-422 DOI: 10.1674/0003-0031(2005)154[0412:PCITWN]2.0.CO;2

Shine, R. (1978). Sexual size dimorphism and male combat in snakes Oecologia, 33 (3), 269-277 DOI: 10.1007/BF00348113

2 comments:

Dale Hoyt said...

You might remember a very popular television mini-series, Lonesome Dove, starring Robert Duvall and Tommy Lee Jones. In one episode they are driving a cattle herd across a river and one of the cowboys receives a fatal bite from a breeding ball of cottonmouths. I don't recall the specifics, but I think the setting of Lonesome Dove is outside the range of the cottonmouth. As I remember it the cattle drive started in trans-Pecos Texas and went north. You could probably get details from the Larry McMurtry novel on which the series was based. I recall thinking at the time that it shouldn't be possible to encounter a cottonmouth where they were.

David Steen said...

Hi Dale,

From the best I can determine, you're right. If we are to define Trans-Pecos Texas as west of the Pecos River then it is further west than the known range of the Cottonmouth, although it looks as though the species may have been found near the mouth of the river where it empties into the Gulf of Mexico. If Duvall and Jones did head north from Texas, they wouldn't have encountered Cottonmouths up there either. Good eye.

The geographic range of the Cottonmouth will be the topic of a future Cottonmouth myths column.

Dave