The Wasp Empire has subjugated a significant number of other kinden within its borders. One way which these cities are kept suppressed is by the practice of taking Auxilians. This also helps to keep their large armies manned.
A portion of the fighting men of a conquered city are conscripted into the Imperial Army. The role they carry out is dependant upon their capabilities, but are always military. Heavy infantry, police, engineers and so forth: basically filling every role that the Wasps cannot or will not do themselves.