Geographic variability of the thoracic chaetome in females of Coquillettidia richiardii (Ficalbi, 1889) and Culex modestus Ficalbi, 1890 was revealed for the first time. We found statistically significant differences in the number of setae between populations from various regions. In particular, Coquillettidia richiardii females from Romania and Moldova have on average a greater number of postpronotal and prealar setae as compared with conspecific females from St. Petersburg and Leningrad Province of Russia. Culex modestus females from Uzbekistan, Kyrgyzstan, and Leningrad Province have on average fewer postpronotal, prealar, mesepisternal, and upper mesepimeral setae than the females from Rostov Province of Russia.