1. The interspecific relationship between the distributions of consumers and resources is examined, using data for macrolepidoptera (moths) in Britain.

2. Monophagous moth species feeding on host plants with small geographical ranges also have small ranges, whilst those feeding on host plants with large ranges may have small or large ranges themselves. Likewise, there is an approximately triangular relationship between the proportion of the range of its host that a monophagous moth occupies and the size of the host range.

3. Most monophagous moths occupy a small proportion of the range of their host, and only feed on hosts that have relatively large geographical ranges.

4. Factors determining both the range size of a monophage and the proportion of the host plant’s range that it occupies are independent of taxonomy.

5. Monophages tend to have smaller geographical ranges than congeneric polyphages, but do not occupy a smaller proportion of the ranges of the plants that they consume.