Small Heath

Coenonympha pamphilus

General Distribution and Status

The Small Heath is widespread in Britain and absent only on the highest mountains and the far north of Scotland. It was probably always widespread but many colonies were lost in the last century owing to farming improvement and cessation of grazing. Since the 1970s there is concern that colonies are still dying out and existing colonies at monitored sites much less abundant than they used to be (Brereton et al., Fox et al.). Possible reasons are habitat fragmentation, overgrazing and climate change (Asher et al.). In Hertfordshire and Middlesex, there was a partial recovery at the beginning of 2010s but despite a setback in the middle of the decade (Wood, 2016) numbers have picked up again. 2021 and 2022 were disappointing years, however, with abundance well down especially ln the late summer.

UK distribution map
UKBMS Species summary (2020)

Habitat Requirements

This species is found on grassland where the sward is kept short and is most common on well-drained soils like chalk downland, heaths and coastal dunes. Smaller colonies can occur in woodland rides, roadside verges, disused quarries, waste ground and even large gardens.

Larval Foodplants

Sheep's Fescue Festuca ovina (Thomas & Lewington) is probably most frequently used. Bent Agrostis spp, Meadow-grass Poa spp.

Adult Food Sources

Buttercup Ranunculus sp. (41), Cinquefoil Potentilla sp. (36), Devil's-bit Scabious Succisa pratnsis (25), Common Bird's-foot Trefoil Lotus corniculatus (17).

Historical Records

The earliest reports indicate that the butterfly was common and widespread in Hertfordshire. Foster's 1937 report refers to it as 'abundant everywhere'. It was still common in the 1970s according to Waterton's 1970-81 report.

Local Distribution and Abundance

As shown on the map, the Small Heath occurs in the majority of tetrads in the Stevenage area but curiously the tetrads indicating absence contain grassy habitats which might be suitable for the butterfly. An estimated number of 50 near Watery Grove were seen on 13 July 2001 but about two-thirds of the reports submitted are for only one or two individuals. Knebworth Park, Frogmore Gravel Pit and Great Ashby Park are the best sites. In 2016, it was a poor year with only eight records submitted and nowhere were there more than two individuals counted on any one visit. 2017 was a much better season, however, with double-figure counts obtained on two occasions at Frogmore Gravel Pit on 25 May and 1 June. There was continued improvement in 2018 with some double-figure counts in Knebworth Park and more than two-thirds of all the records in that year reported in August and September. My observations indicate that 2019 was the best year on record with good numbers throughout the flight season. A report of two sightings at Little Wymondley on 23 June 2019 is the first in the TL22D tetrad since 30 August 1999. Generally, 2020 appeared to be have been better in terms of abundance with an average of approximately five specimens for each report compared to between three and four in 2019. There was a first record since before 1995 for the TL22J square in 2020 when a Small Heath was seen at the Chesfield Downs golf course on 16 June. Although there was a good first brood in 2021 numbers were low in late summer probably due to the mainly dull and cool conditions. 2022 was another relatively poor year with only one visit yielding other than a single-digit count - 15 off Ford Lane, Aston on 11 June. On the other hand, there were reports from two tetrads for the first time in 2022 on 16 June: Nursery meadow, Weston (TL22P) and off Walkern Road near Aston (TL22X). 2023 was a better year for the Small Heath with higher numbers in the spring than late summer. There was a first record during the survey for the TL22Z square (Cromer area) when several specimens were seen on 3 June 2023.

Transect weekly counts

Stevenage (South Fairlands Valley Park) transect 1993-2023

Before the Small Heath disappeared in 2000 the first year of the survey was the best year for the butterfly. All the specimens recorded in the 1990s were found in Canyon Field as it was then known. On 29 May 1993, 12 individuals were seen. The dramatic decline in the 1990s resulted from neglect in this field which became overgrown with shrubs and no patches of fine grasses upon which the butterfly depends. It was not seen again until 2013 when one individual was found about 100 metres north of the Scout Activity Centre. The recent cutting regime in the park may be benefitting the butterfly. 2019 saw a dramatic increase in numbers where most were discovered at Shackledell Grassland and the grassland strip to the west of it. However, 2020 was a disappointing year. One possible reason considering the increase in populations elsewhere is human disturbance of the habitat. The long drought in 2022 probably contributed to a big fall in numbers with only three seen all summer.

Knebworth Park transect 1996-2010 and 2017-2023

Fortunes continue to improve for this butterfly and 2020 was easily the best year during the survey with most specimens found in the north-western section of the park as in previous years. It is possible that extensive deer grazing has benefited this species although numbers dropped back on 2021. As for the Stevenage transect there was a significant drop in numbers in 2022.

Knebworth Woods transect 2017-2023

No Small Heaths were reported here in 2017 but several were seen in the field just south of Norton Green Common in 2018 and populations continued to increase when in 2020 at least half a dozen individuals would sometimes be seen. Numbers fell in 2021 especially in late summer. Although numbers overall in 2022 were similar to 2021 the vast majority were seen in August and September. A dramatic fall in numbers in 2023 is likely due to coarse grasses allowing to dominate around Norton Green Common in the summer.

Pryor's Wood transect 2000-2022

2019 was the best year for this species in line with the other two local transects with five specimens counted including three on 20 June. Prior to 2019, only five records (all of single individuals) were recorded in 2006 (2), 2011 (2) and 2015 (1). Three individuals were seen in 2020, one in 2021 and two in 2022.

Life History

Earliest date: 3 May 2011 at Frogmore Gravel Pit
Latest date: 1 October 2015 at Frogmore Gravel Pit

Two or three generations are produced each year but they often overlap so the butterfly can be seen anytime between May and September. About 95% of records used to compile the phenology chart were from the 1990s coupled with the comparatively small number of records may not totally reflect the situation today. Eggs are laid singly on a grass blade. Larvae spend much of their time at the bottom of a tuft of grass but will feed at night on the grass tips (Eeles). Larvae will either hibernate or develop to form pupae suspended on a grass stem.
More details on the UK Butterflies website

Behaviour/Observation notes

Males are very active when patrolling over open grassland around a suitable landmark in search for females but in the early morning or during cloudy weather they should be more approachable when perched on the ground. Mated females will stay in the vicinity of the foodplants and can be approached with ease. The butterfly always basks with its wings closed.

Variations/Aberrations

There is a form ssp. rhoumensis from Scotland where the specimens are duller than the English form with the hindwing undersides looking mainly grey and the white band narrower or absent. There are many classified aberrations in relation to the colouring and markings on the wings but none have been reported from Hertfordshire.
Find out more on the UK Butterflies website