the habitat of meadow margins and hedges; field gates are often in such locations, thus the gatekeeper can be found much more frequently in such locations than the meadow brown, for example. Recent expansion and genetic diversity Early in the 20th century, P. tithonus was common in southern Britain, but sparse in the north. In fact, the population contracted before re-expanding beginning in the 1940s. Over the past three decades, the flight range of the gatekeeper has extended northwards in Britain. Furthermore, the length of the flight period has been observed to be significantly shorter close to the edge of the range, suggesting that the extension of flight period and expansion of range are likely to be related. However, the mean flight date and length of flight period are not related. Larger individuals have been found to cover longer distances, and this recent expansion of the gatekeeper may explain the larger size of recent populations. As a result of recent expansion, the gatekeeper is found in a wide variety of habitats. Some of the largest colonies can be found in scrubby grassland, woodland rides, country lanes, hedgerows, and other similar conditions within its range. This has led to a greater degree of genetic diversity in the gatekeeper compared to other species, such as P. aegeria, which are seen in more limited habitats. However, the contraction of abundance in the early 20th century has limited the potential of this genetic diversity, as bottlenecks and repeated founder events could have occurred during range changes. Much of the data on changes in P. tithonus population size has been gathered from the UK Butterfly Monitoring Scheme, which has recorded changes of abundance for 71 species between Britain and Ireland since 1976 through visits to more than 1500 monitoring sites. Food P. tithonus is a characteristic field-margin species; it feeds on grasses as larvae and nectar as adults. The larvae of the Satyrinae all feed on grasses, such as rough meadowgrass (Poa trivialis), smooth meadow grass (Poa pratensis), and sheep's fescue (Festuca ovina); they are usually green or brown. The pupae are a flimsy chrysalis either hanging upside down or lying in grass. The adults are often found around blackberry plants. The adult butterfly has a short proboscis and the shallow flowers of the blackberry provide an excellent nectar source. Larval food plants The primary larval food plants are bents (various Agrostis species), fescues (various