Male stable flies require at least one or more blood meals to reach sexual maturity and are often caught in CO₂- baited traps. We tested the hypothesis that young male stable flies (one to three days, one blood feeding session) would be more responsive to CO₂ bait than older male stable flies by monitoring the upwind movement of different-aged male stable flies exposed to CO₂ using a wind tunnel. The proportion of males moving upwind toward CO₂ decreased with age (days), from 49% for males <= 3 days old, to 4.5% for males > 3 days old. To further test this, we conducted daily sampling of stable fly populations at a beef farm using a CO₂-baited cloth trap. We found that days on which a high proportion of males were caught, females were predominantly from early developmental stages, indicating that proportionately more males were caught from field populations made up of younger cohorts. These results were consistent with the wind tunnel experiment patterns.