The ecological function of scorpion fluorescence under ultraviolet light is unknown. In fact, no response of any organism to scorpion fluorescence has been documented. To determine whether or not some potential prey, specifically aerial insects, respond to scorpion fluorescence, I compared the number of aerial insects captured on sticky traps containing fluorescent scorpions to the number captured on traps containing non-fluorescent scorpions during both full and new moons. The results show that aerial insects avoid fluorescing scorpions during the full moon, when fluorescence is at its peak, but not during the new moon when it is weakest. Avoidance of fluorescing scorpi-ons by potential prey is likely to reduce the scorpions’ prey capture rate. This apparent cost of fluorescence highlights the likelihood that fluorescence has a positive function which maintains the trait in spite of this cost.