Re: Why are there are no skunks in England and no snakes in Ireland?

Skunks are exclusively New World animals.  There are several species of 
them (some found only in North America, some only in South America, some 
whose geographic ranges bridge the two continents) but they all have a 
common ancestor that migrated across the land bridge from Asia and then 
diverged into different species in the New World.  (Relatives of skunks 
in the Old World include various species of weasels, such as ermine, 
mink, and an animal that looks a lot like a skunk, and sprays like a 
skunk, the zorilla).  

Of course, many animals that evolved in one location end up in another 
location either by dispersing or because humans moved them.  The former 
usually happens either when an animal that can fly makes it to a new area 
under its own power, or when it is carried by a bird or by a log floating 
in the ocean.  For skunks, which obviously don't fly, it would be extremely 
difficult to get to England accidentally since it is such a long distance. 
 And it seems highly unlikely that any human would intentionally transport 
a skunk there!  If skunks were to end up in England, however, they would 
probably be quite happy.  Skunks eat almost anything (insects, small 
vertebrates like lizards and mice, bird eggs, berries, roots) and are very 
adaptable in terms of weather and habitat (esp. the striped skunk, which 
ranges from Mexico to Canada and coast to coast in North America).  They 
are also well-equipped to fend off predators!

I suspected that the answer to why there are no snakes in Ireland would be 
the same sort of answer as why there are no skunks in England--they just 
never got there.  Just to be sure, I asked a friend who studies snakes, and 
he confirmed that the Irish Sea could easily have prevented snakes from 
dispersing to Ireland.  He also suggested that, unlike skunks in England, 
snakes in Ireland would not be too happy, if they got there.  The Irish 
climate is cool and wet, and the topography is pretty flat--all things that 
snakes _don't_ like.  Apparently, attempts have been made to introduce 
grass snakes to Ireland (usually done surreptitiously by individuals, and 
invoking the rage of most Irish) but these have failed.  Such failures 
could simply be due to the small numbers of snakes introduced, or to the 
unappealing (to snakes) climate, or to a combination of these factors.