Invasive animal pests inflict many kinds of damage on the environment, and threaten native fauna and flora. We attempt to value the benefits from the extra biodiversity that is protected if these threats were removed. The NSW Rural Lands Protection Board is a major agency that undertakes pest control, and is organised into 48 districts across the state. A cross-sectional set of data on Board expenditures, pest abundance, and environmental and climatic characteristics, was compiled by district and analysed. The number of threatened native plant and animal species increases with pest abundance and with the total number of native species present in the district. But the number of threatened species decreases as Board expenditures on pest control increase. The value of preserving an extra species is derived from these changes in expenditure, following conventional economic principles. Then the potential gain in economic surplus is estimated if the threats to biodiversity were removed. The results so far suggest that the value of the total benefit of protecting an extra species is at least $44,250 per year, and the potential gain in surplus for New South Wales if the threats were removed is at least $132m per year. This change in surplus is also the total economic loss because invasive pests threaten native flora and fauna. If only half the native species could be protected, the avoidable economic loss is at least $95.7m per year. The assumptions and limitations of these estimates are discussed.