* Шмель (shmel) is the most common and general term for "bumblebee". It's the most accurate translation.
* Земляная пчела (zemlyanaya pchela) literally means "ground bee" and can also be used for "bumblebee".
* Шершень (shershen) is more specifically a hornet, but it can sometimes be used colloquially for "bumblebee" as well.
Therefore, the best translation for "bumblebee" in Russian is "шмель" (shmel).