I've never noticed any Stormtroopers other than humans. The various Stormtroopers, Snowtroopers, Sandtroopers, and Scout Troopers armor always seems to be shaped for humans. Do the novels shed light on Stormtroopers that weren't human? If so, what other species were employed?
In a recent ( less than two years ago) Dark Horse comic series starring Jaina Solo, the new Empire employed at least human and Trandoshan Stormtroopers.
Following Jao's escape, Empress Marasiah Fel had assigned Ania with a mission to rescue Jao Assam and provided her with an escort force of Trandoshan stormtroopers.
It's likely that either there weren't any or they were at least few and far between. There are two reasons for this:
- The Empire was speciesist. The officers are all human as well, and in the EU it's established that they have quite pro-human policies that make it difficult for non-humans to succeed within the military. There's also the logistical problems- the cost for manufacturing things decreases the more you produce, so it would make financial sense to, if you can, use a single species with one set of requirements.
- Many stormtroopers, as of the start of the Clone War, are clones of a single human, Jango Fett. This was established in the films. In the EU it's established that the Empire took over Kamino, where the clones were created, using their own creations so that they could be coerced into creating more. I'm not sure what proportion of the Imperial Army were clones at the time of the Clone Wars, but it can be assumed it was a substantial amount. However, this would have declined sharply as no more were being created (according to Legends), so there may have been a low number by the time of the destruction of the first Death Star.