RAUK - Archived Forum - feeding habits question

I have a question about grass snake feeding habits; we know that some grassies (individuals and populations) avidly take common toads whilst others don't seem to.  Is there any evidence that this difference has any genetic basis or is it simply that a hatchling faced with nothing but toadlets will become habituated to the presumably more challenging / distasteful meal of a toad and graduate to bigger toads if in a frog-free zone ?  If the latter, can a frog-eating grassy adapt to a change in circumstances and start eating toads if frogs become less plentiful ?

Cheers, Will

There isn't really any research on why some grassies exhibit this behaviour, it just seems that some of them have a preference for e.g. toads, which could just be due to toads being the most nourishing compared to energy expenditure, or it could well be habituation.

I wouldnÆt class a toad as a challenging / distasteful meal to a grass snake anyway, the toads secretions donÆt affect them apparently and all that inflating they do to make them selves look big àà pah, grassies just laugh à as they slowly consume them à. pushing the air out like a whoopee cushion .. mmm

These animals could well be feeding on other creatures as well, unless we watch the animals 24/7 and more importantly all year round, we canÆt be sure. But I think grass snakes are adaptable enough to change diet if circumstances change.

Will native Natrix in captivity will take live fish, newts, frogs or toads without hesitation regardless of the animals apparent previous preferences, the important issue seems to be the movement not the specific prey item.

Most will instantly adapt to eating goldfish in captivity. From my very early observations of a 'toad' eating population, i.e. one where the norm was for toads to be regurgitated on capture, specimens from the population would avidly feed on palmate newts, frogs or any small fish if they were offered in captivity. Palmate newts were readily available to this population but I only once saw an adult from this population actively hunting for palmate newts in the wild, though I observed sub-adults taking them regularly.

I think it is entirely down to what is available and what would constitute a satisfying meal. I'm deeply distrustful of studies which show a particular item in the diet as a 'specialism' as it may simply be seasonal abundance or site specific and I believe Natrix to be a generalist.

In my view it could not be proven that there was some form of preference within a population unless it could also be established that the alternative prey item occurred in the same abundance and offered the same nutrition/effort of capture ratio at the site. I simply don't think this is the case with frogs and toads. I tend to think that one tends to find large numbers of common frogs in different habitats to where one finds large numbers of common toads and grass snakes are likely to be found preying on them when either situation occurs and are mobile enough to prey on different amphibian populations as the fancy takes them. So a result of 'toad' eating population becomes very suspect in my opinion, as it most likely reflects 'toads abundant' - hence why the grass snake population is detected.

One strange thing though, I've never heard of a population in the UK that generally regurgitate fish when captive Natrix will happily take them, so perhaps there is generally a bias towards amphibians in wild UK Natrix populations.

Of course the captive situation doesn't really prove anything either, a predator placed in a small space with a possible prey item is very likely to eat it! This might be quite different to the situation when they are actively hunting for prey in the wild.

I ought to point out that my days of throwing palmate newts to grass snakes ended many years ago when doing such things didn't seem quite so un PC  Though I always figured that they would have been eating something if they were in the wild so it didn't matter in the greater scheme of things.

The last captive I had proved to me something I had often wondered about though, many say that native Natrix will convert to dead mice, I have never ever actually observed this, I've seen them sniff at dead mice but never seen the feeding response triggered in a Natrix of native origin by a dead mouse. Some European specimens yes, but never ever one from the UK.

On occasion I have been asked by people who had sick or injured grass snakes in their care what they should do as the animal would not feed on dead food. In nearly every case the answer was to offer live prey which instantly would trigger a feeding response, fish being the most easily obtainable. Hours of wiggling bits of dead trout in front of my last captive proved to me that movement was a key trigger and oddly, that being dead was a very good reason for the grass snake to drop the item instantly after striking at it.

Gemma,

about the fish thing. I know and have photographs of many incidents in EF where Natrix take fish in large numbers from small ponds.

Cheers

Rob

• lies,
• damned lies,
  
• and statistics."

The last captive I had proved to meásomething I had often wondered about though, many say that native Natrix will convert to dead mice, I have never ever actually observed this, I've seen them sniff at dead mice but never seen theáfeeding response triggered in a Natrix of native origin by a dead mouse. Some European specimens yes, but never ever one from the UK.

Al were they live or dead voles?

I believe the point of the thread was about certain populations of grass snake that only appear to eat a particular species of amphibian most of the time, whether this is actually the case and why is not known!

From my literature research I found examples of grassies feeding on .... fish, small mammals, nestling birds, invertebrates (earthworms, bees, slugs and juveniles snapping at & consuming robber flies) and reptiles (common lizards and slowworms)

 "On the Greek archipelago of the Cyclades the grass snake predominantly feeds on geckos, lacertid lizards and small mammals"

Very clever buggers!

Al were they live or dead voles?