Gatekeeper

Pyronia tithonus

General Distribution and Status

The Gatekeeper is widespread and common in England, except the far north, and Wales but its range is gradually expanding northwards. The reason for the expansion is probably due to climate change as the butterfly's habitat type is found throughout the country. The removal of hedgerows and fewer field margin habitats had affected this butterfly in the last century most especially in the arable east of England (Asher et al.) . However, since the 1970s expansion has taken place, albeit at a slow rate, but abundance at monitored sites has declined by over a third (Brereton et al.). In Hertfordshire and Middlesex, there has been a very slight expansion in range but with numbers on transect sites decreasing at a similar rate (Wood, 2016) and although 2019 saw a significant increase in abundance, numbers dropped notably in 2021.

UK distribution map
UKBMS Species summary (2020)

Habitat Requirements

This species is a butterfly of hedgerows, woodland rides and scrubland containing tall grasses. Heaths, under cliffs and downland sites are also visited if they contain scrub.

Larval Foodplants

Cock's-foot Dactylis glomerata, Annual Meadow-grass Poa annua, Rough Meadow-grass Poa trivialis, Sheep's Fescue Festuca ovina, Creeping Bent Agrostis stolonifera, Rye-grass Lolium spp.. Common Couch Elytrigia repens is also noted by Sawford.

Adult Food Sources

Bramble Rubus fruticosus agg. (748), Wild Marjoram Origanum vulgare (206), Buddleia Buddleja davidii (174), Common Ragwort Senecio jacobaea (166), Heather Calluna vulgaris (135).

Historical Records

The butterfly seems to have been common, and abundant in some years, throughout the 20th century with no apparent evidence of any significant decline during any period.

Local Distribution and Abundance

The Gatekeeper occurs widely in the Stevenage area. Overall, 2023 was the best year during the survey in terms of number of reports, 275 but abundance is much lower than in the past although 146 were counted during a Wider Countryside Butterfly Survey in the Knebworth Woods complex on 10 July. Hundreds were regularly seen in the late 1990s and the early part of this century in this area. The highest count recorded is an estimated 500 at Knebworth Park on 25 July 2001 reported by Trevor Chapman. Although the overall count is higher at Fairlands Valley Park as indicated on the map many more visits were made to the park during the survey. Some good populations have also been found at Great Ashby Park. 2018 saw a dramatic fall in numbers possibly owing to the hot and dry weather in June which may have left grasses desiccated, impacting larval development although there was a moderate recovery in 2019 and sustained in 2020 to 2023.

Transect weekly counts

Stevenage (South Fairlands Valley Park) transect 1993-2023

The pattern of abundance reflects generally what is occurring elsewhere. The peak in 2004 is pronounced because the conditions in Millennium Wood were ideal for the butterfly in that year. The woodland was previously improved grassland but in late 1999 hundreds of saplings, mostly of oak, were planted and the area was left unmanaged. By 2004, enough scrub had grown in the wood but still with sufficient light and warmth for the butterfly to thrive. However, in subsequent years, the area had become more overgrown and very few Gatekeepers are now seen in this part of the transect. More than half the numbers on the transect in 2004 were found in Millennium Wood, for example, 112 on 31 July against a total of 195. Undoubtedly some specimens dispersed to other areas of the park but the decline in recent years is mostly due to the loss of habitat in Millennium Wood and time will tell if the downward trend will continue. The poor showing in 2016, the worst during the survey with only 83 records can probably be attributed to cloudy conditions in that year. Very little improvement in subsequent years probably due to predominantly dry springs.

Knebworth Park transect 1996-2010 and 2017-2023

Since the peaks in 2004 and 2005, abundance has decreased alarmingly for this species. The counts since the transect was resumed in 2017 appear to suggest an ongoing downward trend. The north-western part of the park is the best area for this species.

Knebworth Woods transect 2017-2023

2019 was the best year after a poor season in 2018 but numbers fell back in 2020 probably due to the effects of the drought in the spring. Numbers continued to decline in 2021 and 2022 although there was a recovery in 2023. The open areas like Burleigh Meadow and the southern end of Norton Green Common suit this butterfly.

Pryor's Wood transect 2000-2022

As with the other transects the species showed a decline in the early part of this decade and although there were reports of the butterfly in 2015 and 2016 after a four-year gap there were no sightings in 2017 and 2018. It was seen on three separate occasions in both 2019 and 2020 but none in 2021 and 2022. The best year was 2003 with 24 individuals and the highest count for a single visit was on 30 July 2001 when 12 were recorded.

Life History

Earliest date: 21 June 2022 at Hitchin
Latest date: 10 September 2007 at Knebworth Park

Only one generation is produced each year. The butterfly's emergence begins in early July and lasts until the end of August with a few stragglers left in September. The peak usually occurs in the last week of July and first week of August. Eggs are laid singly on grasses in warm and sheltered situations but usually in shade. Larvae soon enter hibernation when they emerge. In the spring the larvae feed on the tenderest parts of grass before forming a pupa low down when fully grown.
More details on the UK Butterflies website

Behaviour/Observation notes

The Gatekeeper is often found basking on flowers for long periods in sunlit places and is an easy butterfly to photograph. The female can be confused with the female Meadow Brown for inexperienced observers. Although in most cases, the Gatekeeper has two white pupils in the eye-spots on the forewings and the Meadow Brown has only one, the differences on the hindwings are more reliable to distinguish between the two species. The upperside of the Gatekeeper normally has a white-pupilled eye-spot and the underside a row of white dots.

Variations/Aberrations

Many variations and aberrations appear for this butterfly chiefly relating to the pattern and number of spots. One of the most common aberrations is ab. excessa where one or more dark spots are found under the apical eyespot on the upperside forewings - see photo on the right. I have found this aberration fairly common near Watery Grove. There is an increased proportion of this aberration in the west of England (Barrington). The cloudier conditions in this part of the country may mean that the butterfly has to bask longer with wings wide open to attain optimum body temperature. The extra spots may act as a defence mechanism against predation from birds. Locally, although 2017 saw about double the numbers of Gatekeepers than in the previous two or three years not one ab. excessa was found. Did the fine and dry weather in the early summer of 2017 'normalise' the development of the immature stages to produce more normal specimens? Aberration ab. albida is a form where the ground colour is white and this has been seen in Hertfordshire. I saw an aberration where the hindwing spots are replaced by white blotches at Fairlands Valley Park in 2016.
Find out more on the UK Butterflies website