How many species of black flies are reported in the Twin Cities?

B is the correct answer because recent studies and reports have documented that there are 18 species of black flies found in the Twin Cities area. This number reflects local biodiversity and ecological conditions, including the availability of suitable habitats for different black fly species. Black flies are known for their role in the ecosystem, often serving as indicators of water quality and aquatic health, which may account for the variety within this specific region.

Monitoring the presence of different species can provide valuable data for pest management and public health, particularly since some black flies can be vectors for disease. Understanding the species composition in urban environments like the Twin Cities aids in developing effective control measures and improving the overall management of these insects.