In their Policy Forum “Economic importance of bats in agriculture” (1 April, p. [41][1]), J. G. Boyles et al. address how a decline in bats might affect agricultural returns in the United States. The decline of bats due to factors such as disease and wind farm development is certainly an important issue, and one deserving of policy attention. However, as a motivation for conservation, the ad hoc calculation of the economic importance of bats to agriculture has serious flaws. We would not be able to estimate the total value of cropland across the United States based only on an extrapolation of the per-acre value of cotton in Texas. Factors such as the mixture of crops and their yields, production costs, market prices, and pests all vary greatly across the United States. Similarly, each of these variables plays a crucial role in influencing the economic value of pest control services provided by bats. Additionally, basic natural history tells us that the distribution, abundance, and feeding ecology of bats across widely varying ecosystems is likely to result in substantially different pest control values. By ignoring this variation, the authors' approach to calculating the economic value of bat pest services is tantamount to calculating the nation's gross national product based on a country-wide extrapolation of steel production in Pittsburgh. Boyles et al. 's extrapolation results in the remarkable claim that the value of pest regulation by bats is roughly 50% of the total crop value in states such as Montana, Oklahoma, West Virginia, and Wyoming. Yet the predominant crop in the latter two states—hay—is a crop that Helicoverpa zea (the pest for which the original bat service values were calculated) does not affect. ![Figure][2] In decline. Little brown bat with whitenose syndrome. CREDIT: MARVIN MORIARTY/U.S. FISH AND WILDLIFE SERVICE In the past 15 years, numerous advances in the science of measuring, mapping, and valuing ecosystem services have been made ([ 1 ][3]–[ 3 ][4]). Unfortunately, Boyles et al. 's study ignores these advances and perpetuates most of the early errors that ecologists and economists have attempted to overcome, such as ad hoc value transfers and confounding marginal and total values. The loss of bats is an important policy issue and one we need to take seriously, but studies on the economic value of biodiversity and ecosystem services that can inform decision-making are those that follow state-of-the-art methods in ecosystem service science. 1. [↵][5] 1. I. J. Bateman The Economics of Non-Market Goods and Resources, I. J. Bateman, Series Ed. (Springer, Dordrecht, Netherlands, 1998). 2. 1. I. J. Bateman, 2. G. M. Mace, 3. C. Fezzi, 4. G. Atkinson, 5. K. Turner , Environ. Resources Econ. 48, 177 (2011). [OpenUrl][6][CrossRef][7] 3. [↵][8] 1. N. E. Bockstael, 2. A. M. Freeman, 3. R. J. Kopp, 4. P. R. Portney, 5. V. K. Smith , Environ. Sci. Technol. 34, 1384 (2000). [OpenUrl][9][CrossRef][10][Web of Science][11] [1]: /lookup/doi/10.1126/science.1201366 [2]: pending:yes [3]: #ref-1 [4]: #ref-3 [5]: #xref-ref-1-1 View reference 1 in text [6]: {openurl}?query=rft.jtitle%253DEnviron.%2BResources%2BEcon.%26rft.volume%253D48%26rft.spage%253D177%26rft_id%253Dinfo%253Adoi%252F10.1007%252Fs10640-010-9418-x%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [7]: /lookup/external-ref?access_num=10.1007/s10640-010-9418-x&link_type=DOI [8]: #xref-ref-3-1 View reference 3 in text [9]: {openurl}?query=rft.jtitle%253DEnviron.%2BSci.%2BTechnol.%26rft.volume%253D34%26rft.spage%253D1384%26rft_id%253Dinfo%253Adoi%252F10.1021%252Fes990673l%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [10]: /lookup/external-ref?access_num=10.1021/es990673l&link_type=DOI [11]: /lookup/external-ref?access_num=000086456100002&link_type=ISI