Small heath (butterfly)
The small heath (Coenonympha pamphilus) is a butterfly species belonging to the family Nymphalidae, subfamily Satyrinae (commonly known as "the browns"). It is the smallest butterfly in this subfamily. The small heath is diurnal and flies with a noticeable fluttering flight pattern near the ground. It rests with closed wings when not in flight. It is widespread in colonies throughout the grasslands of Eurasia and north-western Africa, preferring drier habitats than other Coenonympha. However, habitat loss caused by human activities has led to a decline in populations in some locations.
The larval host plants are grasses, found in various habitats, while adult butterflies feed on nectar from flowers. The males of this species are territorial, which plays a large role in obtaining a female mate, and they partake in lekking to establish dominance.
- 1 Geographic range
- 2 Habitat
- 3 Food resources
- 4 Parental care
- 5 Life cycle
- 6 Enemies
- 7 Mating
- 8 Thermoregulation
- 9 Interactions with humans
- 10 Conservation
- 11 Subspecies
- 12 Similar species
- 13 References
- 14 External links
The C. pamphilus is spread throughout the Western Palearctic, particularly in Europe where it has been reported in at least 40 different countries since 2002. It is commonly found in the United Kingdom, largely in England and Wales. Populations are also found in southwest Siberia, regions of Asia, and north Africa.
The small heath is a grasslands species and prefers open habitats with shorter grass compared to other related species. It is also found in an extensive range of environments including meadows, heaths, mountains (in the subalpine zone), and alongside railways. It has been sighted in calcareous grasslands throughout nineteen countries in Europe. For mating and oviposition, small heath butterflies prefer territories that are close to vegetation over areas that are open and clear.
The small heath also resides in biodiverse patches of green habitats (i.e. greenways, gardens, and parks) in urban areas. These fragments create less-isolated corridors throughout cities, which help butterflies disperse throughout this habitat.
The primary food resources for C. pamphilus larvae are different varieties of grass species. These include the Anthoxanthum odoratum, Poa pratensis, Agrostis stolonifera, and Festuca rubra, which commonly appear on some calcerous grasslands.
Adult C. pamphilus butterflies feed on floral nectar of a variety of flowers such as bramble, yarrow, and ragwort. This nectar has a high content of minerals and nutrients (particularly amino acids and sugar), and is highly important for male and female butterfly reproductive success.
Oviposition varies throughout the lifespan of a female small heath. The rate of oviposition is high for young females, particularly at the beginning of their reproductive life, while older females eventually lay fewer and yellower eggs.
Host plant selection for egg laying
C. pamphilus females prefer to lay eggs in grassland. They use a biological adhesive to lay its eggs directly onto host plants, plants near host plants, or wilting leaves. If the eggs are laid on or near host plants, the larvae are able to feed on the host plant. If attached to the dead grasses, they are forced to find their own food immediately after hatching.
Small heath eggs are round and sometimes laid on blades of grass. The eggs are occasionally in clusters, but usually alone. Initially, the egg is a light green with a slight depression on the top and an overall ridged texture. It later gains a white hue with a brown band wrapped around the middle and irregular brown speckles on the surface.
Egg color and weight changes throughout a female’s lifespan. Younger females initially tend to lay heavier, greener eggs at a higher frequency. These eggs then transition to an intermediate green-yellow color. After about 100 eggs are laid, or near the end of their lifespans, older females lay lighter, yellow eggs. Adult small heath butterflies have at least one or usually two broods of offspring depending on environmental factors (such as location and altitude).
By the end of the four instar, the small heath larvae are a leafy green color with a green stripe running along its back and stripes a lighter shade of green on its sides. It has pink anal points, a protrusion at the end of the caterpillar. They typically go through four instars and molt three times. The third instar signals a diapause in which the larva hibernates. Larvae will sometimes go through a fifth instar and enter diapause, which possibly signals an adapted response to environmental factors (primarily temperature). In diapause, the larva’s resources are used to reinforce and strengthen its already-existing larval adult structures. These larvae then develop into larger male and smaller female pupae.
The small heath remains in the pupae stage for approximately 3 weeks. The color of the chrysalis fully develops in four days. The pupa is light yellow-green and suspends from a plant stem with the head facing downward. The cremaster is a series of hooks at the rear of the pupa, which allows it to hang from the stem. The pupae is thick and has a length of 8.5 mm. It is slightly curved with dark dorsal stripes around the sides and light-yellow bumps on the abdomen. The wing covers along the side are a white pigment with small accents of red-brown.
The wings of an adult small heath butterfly are light brown. Males are darker and sometimes have gray-brown hues, while females are paler and occasionally a white-brown or yellow-white color. Other variations include a redder or yellower pigment with the occasional purple-brown color. Both males and females can have a brownish-gray border circling the edge of the wing. This border varies in thickness and appears to be more common in males than in females. The forewing can have a prominent or faint dark spot or, sometimes, no spot at all near the wing tip. The hindwings may also have eyespots or white dots. A white band runs along the underside of the wing and varies in width and fullness. Female small heath butterflies have a wingspan of 37 mm and tend to be larger than males that have a wingspan of 33 mm.
The small heath is diurnal, or is active in the daytime. It flies near the ground with a fluttering flight pattern. Small heaths are also lateral baskers, angling their bodies 90° to the sun with their wings closed when resting.
The Trogus lapidator (parasitic wasp) and other varieties of Ichneumoninae species will often parasitize Lepidoptera pupae as parasitoids. The parasite eventually emerges from the host pupae as an adult by slicing out a cap at the terminal end of the chrysalis and breaking through. In C. pamphilus pupae, staining can sometimes be seen around the cut site of the cap.
Interactions between males
Male small heath butterflies often establish their own territories and become stationary. Males with their own territories are more likely to mate successfully with females. This prompts aggressive male behavior between stationary males and wandering males who may contest territory ownership. Larger males are typically more successful in territorial disputes with other males, as they have longer wing spans and are superior in size and weight to smaller males. Thus, larger males have a significantly higher chance of successfully mating a female.
Temperature plays a role in male-male interactions as well. In low-temperature conditions, it is advantageous for a male to remain stationary and defend his territory. This leads to longer male-male interactions. However, when temperatures are high, choosing not to defend territory is a preferred and advantageous strategy in mating. This leads to shorter male-male interactions.
Interactions between males and females
Male small heath butterflies find mates either by defending their ownership of a territory or by drifting in search for a female. Virgin females also spend time in the air to find a potential mate, but females who have already mated avoid claimed territories. Due to its longer lifespan, virgin females seek mates less urgently than, for example, females of the C. tullia species. Virgin C. pamphilus females will allow males to pass by instead of seeking them out to begin courtship. They choose to perform a long, elaborate zig-zag flight pattern to draw attention after they reach a group of perching males, who will take part in lekking as a show of dominance. The female then selectively chooses her mate and begins a monandrous relationship. Most matings occur with residents within territories than with the wandering non-residents. Females often mate with males with larger wings, as territory owners are usually larger, and generally mate only once or twice in their short overall lifetimes.
Male small heaths aggregate and form leks often around bushes or trees, creating an elaborate visual display home to attract a female's attention. The female will approach by circling the lek, which attracts the males' attention more than being stationary. There are both costs and benefits of lekking for the female. Females benefit by typically mating with the dominant male and producing offspring with beneficial, heritable genes, as a result of their free choice in mates. They also have increased survival and maintained health because males cannot force the females to copulate. A few fitness costs include lost time to obtain more resources, risk of mortality through predation, and less time for oviposition, which all lead to decreased fecundity. The leks themselves do not contain resources for the females.
Copulation between male and female small heath butterflies last between 10 minutes and 5 hours, occurring at any time in the day. In 1985, a study observed that males often mate within their own territory (86.7% of 30 matings), and these copulations are generally lengthy, lasting over 100 minutes. Otherwise, copulations lasted approximately 10–30 minutes, especially for vagrant males. The study also found that either the male or female (but generally the male) is forced to leave the territory after copulation.
During copulation, male small heath butterflies transfer a nuptial gift to a female in the form of a spermatophore, which contains both additional nutrients and sperm. Males can use amino acids found in nectar from food resources to help produce these spermatophores, which are then passed to the female when reproducing. The spermatophore increases female fitness and aids female performance in reproduction, and its nutrients are also assimilated later into the eggs that are laid, leading to heavier larvae.
Small heath butterflies typically live well in dry, open landscapes with higher temperatures, in comparison to other species of satyrine butterflies. When temperatures are significantly high, lifespan is shortened but the C. pamphilus will fare better than shade-dwelling species, such as the speckled wood, Pararge aegeria. Like other butterflies, it has a small range of optimum temperatures and can regulate its temperatures in a small variety of ways, such as positioning its body to maximally absorb sunlight. In high temperature habitats, the C. pamphilus produces eggs at a relatively high rate, has good fecundity, and survives well as compared to woodland butterflies. Male butterflies will also tend to drift and be vagrant in their search for females rather than perch in their territories and wait, as they would do in optimum or sub-optimum temperatures.
Interactions with humans
As a grassland species, the effects of intense, widespread agriculture is a concern for the welfare of the C. pamphilus. Grassland management through periodic ecological disturbances (i.e. mowing) is considered necessary to maintain “semi-natural” grasslands. Negative effects of mowing include the loss of biodiversity, the conversion of natural grasslands into agricultural fields, mortality, and loss of nectar resources. However, a study shows that such disturbances of these habitats may actually lead to an increase in the population of grassland butterflies including the small heath.
Overall, the small heath is generally common and abundant throughout its geographic distribution, particularly in Europe. Urban habitats have become a significant focus in the conservation of the small heath due to the widespread green fragments forming chains of ecological biodiversity. In a study of elevated atmospheric CO2 levels on development, it was determined that larval development time increased due to elevated CO2 levels, suggesting an effect of CO2 on larval performance. Additionally, it was found that food-plant preferences of larvae might also be affected, which could play a future evolutionary role, although this is an area that requires further research.
Status in the Netherlands
In the Netherlands, two satyrine species also of the Coenonympha genus (C. hero, C. arcania) have gone extinct in the past century, and the distribution of one species (C. tullia) is significantly restricted as a result of climate change. One study shows that the C. pamphilus has adapted well to climate change and will continue to survive successfully due to its capability to adapt biologically to altered environments.
Status in England
The small heath, like its cousin the wall brown, has been in serious decline across much of southern England for reasons unclear, and was accordingly designated as a UK Biodiversity Action Plan Priority Species (research only) by DEFRA in 2007. These butterflies typically live in colonies, which have been negatively impacted by construction, human development, and general habitat loss in recent years. In 2007, the IUCN category status listed the small heath as near threatened.
Subspecies of the Coenonympha pamphilus include:
- C. p. lyllus (Esper, 1806) (southern Europe and Siberia, the Crimea, the Caucasus and Transcaucasia)
- C. p. marginata Heyne,  (southern Europe and Siberia, the Crimea, the Caucasus and Transcaucasia)
- C. p. fulvolactea Verity (1926) (middle Asia)
- C. p. centralasiae Verity (1926) (middle Asia)
- C. p. infrarasa Verity (1926) (middle Asia)
- C. p. juldusica Verity (1926) (middle Asia)
- C. p. ferghana Stauder (1924) (middle Asia)
- C. p. nitidissima Verity (1924) (middle Asia)
- C. p. asiaemontium Verity (1924) (Altai Mountains)
- C. p. rhoumensis Harrison (1948)
The butterfly loosely resembles a small meadow brown, but the brown of the wings appears noticeably paler in flight. Unlike the meadow brown and other common members of the Satyrinae subfamily, the small heath is a lateral basker, only ever resting with its wings closed and angled at 90° to the sun. It more closely resembles Coenonympha caeca (forewing without apical spots), Coenonympha tullia (forewing apical spot smaller), and Coenonympha symphita (underside of hindwing without white spot and almost always with a complete row of spots on the forewing).
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