Small Heath

Small Heath Coenonympha pamphilus (Linnaeus 1758)

Family: Nymphalidae, subgroup Satyrinae (The Browns)

Description

Photo above left by Mike Smethurst (same as header)

Photos above middle and right by Paul Simmons. The photo above right shows a paler version of the species

This is a small, brown and orange butterfly about same size as Common Blue or Small Copper. It always perches with its wings closed, therefore its orange upperwings are only seen in flight, when both bright and drab specimens may be distinguished. Perched, it looks rather like a small Meadow Brown, with drab lower wings, and a small but prominent eyespot on the upperwing which is set against an orange-brown background. Small Heaths can be separated from the somewhat larger Large Heath by the latter’s greyer appearance in flight, and multiple eyespots in closed-wing view. Some ID books suggest you can also use habitat to separate the two species. Whilst only the Large Heath is likely to be seen at Thorne and Crowle Moors near Doncaster, both species may be seen flying together on the North York Moors at Fen Bog YWT NR, one of Yorkshire’s few Large Heath sites.

Habitat

It favours rough dry fields with short grass and bare patches (eg animal footprints or tractor tracks) where it usually lays eggs on any of the finer grass species such as the bents, the meadow grasses and the fescues. Sheep’s Fescue Festuca ovina is especially popular. It uses a wide range of grassland including unimproved pasture, grassy acid moorland as well as calcareous grassland. The largest populations in Yorkshire are on the chalk pastures and disused quarries of the northern Wolds. The Small Heath can also be found on coastal cliff tops and sand dunes, along the Humber flood bank, on road and rail verges (especially disused railway tracks), railway sidings and industrial land, and even along sunny, open woodland rides. Although generally favouring dry sites it can sometimes be found in damper areas and even on the edges of marshes as at Fen Bog.

Distribution

The species is widely distributed in suitable habitats throughout the County, with the densest populations in warmer, lower areas, such as Spurn NNR, valley grasslands and quarries in the Wolds and restored colliery and brownfield sites in South Yorkshire. It is thinly but widely distributed over large regions of upland, with small concentrations in areas where there are warm, dry sites, with limited grazing. Rough acid grassland at around 300m on the moorland edges around the Yorkshire Dales provides typical upland habitat, and although it is rare to see two individuals together, many dozens may be observed on a long walk.

Flight seasons on higher ground to the north and west are much shorter and more likely to involve just one brood rather than two or more. Local declines are almost certainly associated with habitat loss and degradation caused by intensive agriculture which has previously been at its most destructive on land below 300m where most of the strongest colonies are found. In the last 15 years there has been an overall decline of 20% or more, but this hides local differences. Numbers in the eastern half of the County have declined, whereas there has been a notable increase in western sites.

Life Cycle

Small Heath has 1 or 2 overlapping broods according to height & weather, with perhaps a small partial 3rd in good years.

Pale green, barrel-shaped eggs are placed singly on grass blades. After laying around 100 eggs females then produce a smaller pale yellow version, the reasons for which are unknown. Eggs become paler with time and develop darker patches, then just before hatching (after about two weeks), they become almost transparent, with the young caterpillar visible inside. Larvae live low in the grass sward and when young, mainly emerge at night to nibble the tips of grass blades. They are green with narrow pale and dark stripes, which provide excellent camouflage in grassy situations.

Growth patterns are complex with 2 broods in the south of Britain (plus an occasional partial third), and only one in the north, with Yorkshire seeing a transitional zone between the two. The situation is further complicated by the fact that a proportion of each brood stay as larvae, becoming well developed by the end of the summer, and ready to pupate early the following year. They overwinter as larvae and may continue feeding throughout winter when mild enough.

The first of the attractive pupae (usually with purple-brown stripes edged with white on the wing cases) are formed by late April, hanging beneath grass stems. The first batch of adults emerges after about 3 weeks, often during May.

These are usually overlapped by adults from the later developing larvae which were offspring of the previous year’s 2nd and 3rd broods, leading to a peak of butterflies in Jun/Jul which is further boosted by offspring of the year. Annual and local climatic variations will influence exactly when this might occur. In good years adults are often on the wing continuously from May to Sept making it difficult to distinguish between generations, and individuals from the previous year which have simply developed at different rates (Blakeley 1997,1998; Whitaker 2001).

The flight stage of individual Small Heaths lasts around 7 days. Males spend most of their time searching for mates. Each establishes a territory near a prominent vegetative feature and perches or patrols the nearby area, occasionally straying more widely. Such territories are defended against other males and spiralling combat flights are commonly seen before one of the participants (often the one with shorter wings!) leaves the territory. Virgin females show extensive solicitation flights, flying back and forth about 1m off the ground. If they enter a territory it is usually to mate. Females will land on the ground whilst the male approaches with fluttering wings and head-butts her. Once mated, females then avoid males and set off in search of suitable open, grassy areas in which to lay their eggs.

Status

The species is not under threat.

Although the butterfly remains fairly widespread it is often in very low numbers and therefore much more likely to be affected by adverse conditions. It could be under greater threat than seems apparent especially as it does not normally appear to fly very far, putting its populations at increasing risk through isolation.

It is particularly vulnerable to the ‘tidying up’ of landscapes by amenity grass mowing and also by ‘conservation’ tree planting on what some people view as grassy ‘wastelands’. Brownfield sites are now subject to increasing development and the subsequent landscaping of what were previously suitable habitats. The species has lost out on intensively farmed grasslands where a fertilized or re-sown sward destroys the fine grasses it requires.

Aberrations


Paul Simmons last updated: 26/11/20