Stuart
Stuart was an insect-like animal kept as a pet by Harcourt Fenton Mudd.

During his captivity by the Klingons in 2256, Mudd trained Stuart to steal food for him and spy on his fellow prisoners via a listening device attached to Stuart's body. 

In December of that year, Mudd used Stuart to spy on Captain  and Lieutenant . After discovering this, Lorca destroyed the listening device and threw Stuart against a wall, nearly killing him. Lorca and Tyler later escaped, leaving Stuart and Mudd behind. ()

Mudd later used Stuart in a devious scheme to free himself from Klingon captivity. However, afterwards Stuart followed his  natural instincts and escaped into the wild. ()

Stuart's species