The “Siberian hamster” is two different species
The terms “Siberian hamster” and “Siberian dwarf hamster” are just another name for the either of the two Russian dwarf hamsters, the Campbell’s dwarf hamster or the Winter White dwarf hamster. Both of these dwarf hamsters can be found in parts of Siberia and that is why they are sometimes referred to as Siberian hamster. All the information in this blog is suitable for Siberian hamsters as they are also dwarf hamsters.
Although they look very similar, the Winter White and Campbell’s dwarf hamsters are actually different hamster species. Despite being different species, they can interbreed and create hybrid offspring. However, this does not happen in the wild though because the two species of hamsters would normally ignore each other or fight.
Siberian hamsters are difficult to tell apart
In case you were wondering what a Siberian hamster looks like, this is a normal winter white:

credit: http://commons.wikimedia.org/wiki/File:Primek_bed.JPG
And the one below is supposed to be a normal Campbell’s dwarf hamster (according to the owner)

By Alexander theo redgrave (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Hybrids of the two Siberian hamster species create problems
Creating hybrids of these two Siberian hamsters can cause many problems. For one, the Campbell’s dwarf hamster is larger than the Winter White so if they are bred and the female hamster is a Winter White, the hamster babies would be too big for her to give birth to and the female hamster would die.
Another reason is that hybrids are more prone to diseases and genetic problems. They also tend to die earlier than the purebred dwarf hamsters.
Sadly, even with these problems, some people crossbreed the two Siberian hamsters because the hybrids can have attractive colors. If you care about your dwarf hamsters, don’t buy hybrids and never breed Siberian hamsters when you are not sure which species they are.