Key to species of Hydrellia from the Saudi Arabia

1. Mesonotum only slightly darker than pleural areas, greenish to tannish gray generally, lacking a contrasted, lateral, mesonotal stripe; anepisternum uniformly unicolorous................................................................. 2

- Mesonotum with broad medial portion mostly brown, contrasted distinctly with lateral mesonotal, grayish stripe from postpronotum through notopleuron; anepisternum golden tan dorsally, gradually becoming grayer ventrally................................................................................................... H. latipalpis Cresson, 1943

2. Anterior fronto-orbital seta in front of anterior ocellus; lunula yellowish; antenna with four aristal rays; presutural dorsocentral seta lacking...................................................................... H. griseola (Fallén, 1813)

- Anterior fronto-orbital seta behind of anterior ocellus; lunula whitish; antenna with five aristal rays; presutural dorsocentral seta present............................................................................ H. maura Meigen, 1838