Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
The flight mechanism and aerodynamics of the bumblebee (as well as other insects) are actually quite well understood, in spite of the urban legend that calculations show that they should not be able to fly. In the 1930s a German scientist, using flawed techniques, indeed postulated that bumblebees theoretically should not be able to fly, although he later retracted the suggestion. However, the theory became generalized to the false notion that "scientists think that bumblebees should not be able to fly."