Question on Grass snake mating

[Ilian Velikov]

Last weekend (24.03.2012) while on a walk with my girlfriend near London, I saw two grass snakes mating. They were coiled next to the footpath with the female on top and the male underneath her. Only the female was able to see us and after a couple of minutes she got fed up with us standing there and watching, so she retreated in the vegetation draging the still attached oblivious male with her. I've never seen Grass snakes mating that early in the year but that's due to the nice weather conditions I guess. Usually when Grass snakes mate they form that ball of many males around one female which I'm sure most of you are familiar with. However these snakes were only two and no other males anywhere near them. So my question is - Is there any reason for that mating ball of males and one female other than that they all happened to be in the same place = does this help the female in anyway to select the most fit male or is it just a matter of who will reach the female first?

[Michal Szkudlarek]

The strongest male is honored to give genes. It is important for female- provides that her babies will be possibly the healthiest.

[Ilian Velikov]

The strongest male is honored to give genes. It is important for female- provides that her babies will be possibly the healthiest

Well, why this female mated with the first male she met than, withouth "testing" others ? Is it posibble that there has been a mating ball, this male won and the others just went away before we found them? How long does the copulation last?

[Berislav Horvatic]

Is there any reason for that mating ball of males and one female other than that they
all happened to be in the same place?

http://onlinelibrary.wiley.com/doi/10.1 ... x/abstract

...several males may simultaneously court a single female, resulting in a ‘ball’of mating snakes
in which each male ‘combats’with rival males by ‘tail wrestling’(see Madsen & Shine, 1993)

http://vipersgarden.at/PDF_files/PDF-1010.pdf

[Ilian Velikov]

Thanks a lot for the articles Berislav! Yes, I knew the ball is a competition between the males, but wanted to make sure because it seemed strange to me that this mating pair were alone with no other males or females around them and I started to wonder if we've missed the mating ball and this single male was the winner, or the two snakes met on their own and mated without forming a ball with other individuals.

[Mark Barber]

From New Naturalist - Amphibians and Reptiles - Beebee and Griffiths - 2000

Large females seem more attractive than small ones to male snakes. This may be because large females produce the most pheromone or perhaps simply because big females are the easiest to find. As they produce the largest clutches of eggs it is clearly beneficial for males to mate with them whenever possible, since by doing so males increase their own reproductive success.

How big was your female, if she wasn't huge this may be a possible theory?

Also

In, Italy, Luiselli (1996) watched 43 copulations in free-living grass snakes, 17 of which were single pairs with the remaining 26 comprising mating balls of a female with three to eaight males .........
Luiselli speculates that the incidence of mating balls in grass snakes may be related to climatic factors and might be highest in the north. At high latitudes the cold climate permits only a relatively short mating season. As not all females emerge from hibernation at the same time it is likely that the sex ratio will be skewed towards males and this will increase competition for females, and thereby likelihood of mating balls.

So in the UK as we have a long mating period, at any one time there will be less females compared to males, thus we should have more mating balls?

Oddly, though, mating balls have rarely been observed in British snakes.

I have heard of numerous mating balls being seen in South Wales over the last few years.

In my opinion it has to somewhat site specific - snake density and hibernation site potential etc. I.e. the more snakes there are and the more closely they hibernate to each other, the increased chance of mating balls taking place?

[Ilian Velikov]

How big was your female, if she wasn't huge this may be a possible theory?

I would say she was medium sized, neither too big nor too small! However, the male looked quite small. If I hadn't seen them mating I would've thought he was a juvenile/not yet mature. It's interesting that in most animals either the female or male makes the choice of a mate, while with grass snakes both sexes have a choice - males choose the larger females and females choose the strongest males.

Maybe the pair we saw were the "rejects" that couldn't find a mate within the ball..who knows?!

[Michal Szkudlarek]

Mark, can You explain why in Your opinion there is a dependence between length of mating season and mating balls commonness?

[Berislav Horvatic]

Luiselli speculates that the incidence of mating balls in grass snakes may be related to climatic factors and might be highest in the north. At high latitudes the cold climate permits only a relatively short mating season. As not all females emerge from hibernation at the same time it is likely that the sex ratio will be skewed towards males and this will increase competition for females, and thereby likelihood of mating balls.
So in the UK as we have a long mating period, at any one time there will be less females compared to males, thus we should have more mating balls?
Oddly, though, mating balls have rarely been observed in British snakes.

If a short mating season (at high latitudes or altitudes) should mean more mating balls, then
why should a long mating period in the UK also imply more mating balls? I don't get it.

And if mating balls have rarely been observed in British snakes, this would be in accordance
with a long mating period in the UK, not at odds with it. So why your "Oddly, though,..."?

[Jeroen Speybroeck]

There's a BBC doc (herp episode of Life series) that nicely shows the thermoregulation in such 'balls', with the cold female arriving amidst the hot males. If I remember well, some males cheat by producing female pheromones, thus attracting other males which share their bodyheat with him.

Interesting stuff...