Gatwick's butterfly transects - 2019 (Year 2)

The two transects under the UK Butterfly Monitoring Scheme (UKBMS) commenced at Gatwick in 2018 and have been continued in 2019. These intensive surveys are brilliant at providing an in-depth picture of butterflies on our sites, but also results in a weekly site walkover covering a large area, providing a good opportunity to collect additional species records throughout summer.

River Mole, North West Zone

Upper Picketts Wood, Land East of the Railway Line

2019 was the first full year for weekly transects in the Land East of the Railway Line (LERL), which had first begun mid-way through 2018. Across both the North West Zone (NWZ) and LERL, the average survey temperature was 18.7 °C, with sunlight at 73% in NWZ and 78% in LERL. 24 weeks out of 26 were completed in the NWZ; two were missed due to inclement weather early in the year. 21 weeks out of 26 were missed in LERL, again due to inclement weather but the final two weeks there was no access to this site.

Purple Hairstreak (Favonius quercus), LERL

Green Hairstreak (Callophrys rubi), NWZ

The highlight of the year for all of us must have been seeing Grizzled Skipper (Pyrgus malvae) in the NWZ for the first time since 2016; this is a Section 41 species of principal importance under the NERC Act in England. It typically occurs in small colonies, and on our well-recorded site it seems this species may occasionally fall under the observational threshold.

Grizzled Skipper (Pyrgus malvae)

Grizzled Skipper - aberrant form

Another surprise was finding Marbled White (Melanargia galathea) in the Land East transect along the Y-lagoon footpath; it is likely to have blown over from the Gatwick Stream floodplain. We have many records of this species along the stream banks and the River Mole.

Small Tortoiseshell (Aglais urticae) seemed to do better than last year (with only 2 spotted in the NWZ in 2018). This year in NWZ, 6 individuals were seen in the first week with the odd individual spotted throughout the summer. A single individual was reported on 3 separate occasions in LERL.

An influx of Painted Lady (Vanessa cardui) showed up in LERL toward the end of June, with a peak count of 8. In NWZ there was another influx as 10 individuals were counted in mid-August. Vince then confirmed breeding on site when he discovered caterpillars feeding amongst thistles.

Painted Lady caterpillar

Painted Lady

Clouded Yellow (Colias croceus) and Brimstone (Gonepteryx rhamni) were missing from the NWZ transect this year.

White-letter Hairstreak (Satyrium w-album) was seen just outside of LERL transect in 2018 and counted as a roving record, but was missed entirely from the site this year. The species is often recorded on the northern section of the River Mole, which is off the NWZ transect. Purple Emperors (Apatura iris) have been previously seen here too; a lone female was seen egg-laying in 2016.

Dingy Skipper (Erynnis tages) typically occurred in good numbers in the NWZ (a peak count of 10 were seen on one day). Roving records have previously picked up this species in LERL 2016, but it has not been seen since.

Brown Hairstreak (Thecla betulae) occurred on both transects again this year, however in slightly lower numbers (a peak count of 2 compared to 5 in the NWZ in 2018).

Silver-washed Fritillary (Argynnis paphia) were in good numbers in LERL in this year, with a peak count of 9 in mid-July. Also good numbers of White Admiral (Limenitis camilla) were seen along the woodland glades in LERL, although most were just outside of our transect.

River Mole grasslands

Out of a potential 33 species, 30 species in total were recorded across the transects this year, not inclusive of the White-letter Hairstreak in LERL which counts as a roving record. A peak count of 633 individual butterflies occurred in the NWZ on July 1^st 2019 - that was a long day! The highest species count on any one day was 20 in LERL on July 16^th. The species total for NWZ was 28 (one less than last year) and 27 for LERL.

The below table shows the last recorded year of all butterfly species in the biodiversity areas at Gatwick, based on our butterfly survey data and roving records from 2012 to present day

Common name	Species name	NWZ	LERL
Brimstone	Gonepteryx rhamni		✔
Brown Argus	Aricia agestis	✔	✔
Brown Hairstreak	Thecla betulae	✔	✔
Clouded Yellow	Colias croceus
Comma	Polygonia c-album	✔	✔
Common Blue	Polyommatus icarus	✔	✔
Dingy Skipper	Erynnis tages	✔
Essex Skipper	Thymelicus lineola	✔	✔
Gatekeeper	Pyronia tithonus	✔	✔
Green Hairstreak	Callophrys rubi	✔
Green-veined White	Pieris napi	✔	✔
Grizzled Skipper	Pyrgus malvae	✔
Holly Blue	Celastrina argiolus	✔	✔
Large Skipper	Ochlodes sylvanus	✔	✔
Large White	Pieris brassicae	✔	✔
Marbled White	Melanargia galathea	✔	✔
Meadow Brown	Maniola jurtina	✔	✔
Orange-tip	Anthocharis cardamines	✔	✔
Painted Lady	Vanessa cardui	✔	✔
Peacock	Inachis io	✔	✔
Purple Emperor	Apatura iris
Purple Hairstreak	Neozephyrus quercus	✔	✔
Red Admiral	Vanessa atalanta	✔	✔
Ringlet	Aphantopus hyperantus	✔	✔
Silver-washed Fritillary	Argynnis paphia	✔	✔
Small Copper	Lycaena phlaeas	✔	✔
Small Heath	Coenonympha pamphilus	✔	✔
Small Skipper	Thymelicus sylvestris	✔	✔
Small Tortoiseshell	Aglais urticae	✔	✔
Small White	Pieris rapae	✔	✔
Speckled Wood	Pararge aegeria	✔	✔
White Admiral	Limenitis camilla		✔
White-letter Hairstreak	Satyrium w-album

Total no. species

NWZ = 28

LERL = 27

Species previously recorded but not detected on one or both transects in 2019

Common name	Species name	NWZ	LERL
Brimstone	Gonepteryx rhamni	2018	2019
Clouded Yellow	Colias croceus	2018	2017
Dingy Skipper	Erynnis tages	2019	2016
Purple Emperor	Apatura iris	2016	-
White Admiral	Limenitis camilla	2017	2019
White-letter Hairstreak	Satyrium w-album	2019	2018