The energetics of mosquito feeding by insectivorous bats

Dietary studies have long shown that insectivorous bats do not often consume mosquitoes, despite cosmopolitan distribution and occasional ubiquity of mosquitoes (Culicidae). The apparent avoidance of mosquitoes relative to availability may relate to their small size, as bats may have difficulties detecting and capturing mosquitoes or they may not return sufficient energy per unit effort of capture. We used bomb calorimetry to determine the energetic content of mosquitoes from Alaska and Illinois, USA, and compared resulting estimates to daily energy expenditure of several bat species. On a per gram basis, mosquitoes were energetically comparable with other insects (26.82 +/- 2.40 kJ/g dry mass); however, an individual mosquito contains little energy. Some small insectivorous bats could theoretically meet daily energy needs by foraging exclusively on mosquitoes for <2 h, assuming maximal estimates of the rate of successful capture of mosquitoes. Larger, omnivorous bats may require >25 h of foraging on mosquitoes to meet daily energy needs. Wet mass of the mosquitoes required to balance energy budgets represent 18%-92% of body mass of bats and tends to be higher for smaller species. Thus, it appears that a mosquito-based diet may be constrained by different factors in small and large bat species.