[1] Given its preference for warmer weather, the restriction of range expansion can be assumed to be due to climate.

[clarification needed] Colonies vary in size depending on the available habitat, and can range from a few dozen to several thousand butterflies.

[2] Named for its rigorous patrol of hedges and woodland rides, the gatekeeper butterfly is a prime pollinator.

A large number of aberrant forms are known, such as excessa, where specimens have two to four extra spots on the fore wing upperside.

[7] The male has a dark patch on the upper side of the fore wing that contains scent-producing scales known as the androconia.

Some of the largest colonies can be found in scrubby grassland, woodland rides, country lanes, hedgerows, and other similar conditions within its range.

[2] 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.

The adult butterfly has a short proboscis and the shallow flowers of the blackberry provide an excellent nectar source.

), carline thistle (Carlina vulgaris), devil's-bit scabious (Succisa pratensis), fleabane (Pulicaria dysenterica), hemp agrimony (Eupatorium cannabinum), wild privet (Ligustrum vulgare), ragwort (Jacobaea vulgaris), red clover (Trifolium patense), thistles (Cirsium and Carduus species), thyme (Thymus praecox), and water mint (Mentha aquatica).

[13] The gatekeeper is a relatively active butterfly, but not very mobile, as seen when comparing it to a similar species, Maniola jurtina.

As a result, females usually only mate once, so they have more time available for resting, nectar feeding, host plant selection, and oviposition.

[14] This weather trend may explain why P. tithonus numbers have been low in northern Britain because of the cooler summers and that range expansion has resulted from climate change.