Abstract: I review the distribution of ant genera in cold biomes of the northern hemisphere, and discuss opportunities and challenges in using ants as environmental, ecological, and biodiversity indicators in these biomes. I present five propositions that, if supported with future research, would allow ants to be used as biological indicators in north-temperate cold biomes: (1) Distribution of individual species or species groups are leading (early-warning) indicators of climatic warming at tundra / taiga or taiga / broadleaf forest boundaries; (2) mound-building species in the Formica rufa Linnaeus, 1761 group are ecological indicators for land-use changes in European taiga and broadleaf forests; (3) relative abundance (evenness) is a leading indicator of environmental changes whereas high species richness is an indicator of past or ongoing disturbance; (4) presence of social parasites and slave-making species are better indicators of ecological integrity than presence or abundance of their hosts alone; (5) occurrence of non-native or invasive species is an indicator of reduced ecological integrity. Important aspects of long-term sampling, surveying, monitoring, and experimenting on ants are discussed in light of future research needs to test these propositions and to further develop ants as indicators of changing environmental conditions in north-temperate cold biomes.