Dark Green Fritillary [Argynnis aglaja]
Male Dark Green Fritillary. Males are mainly consistent in appearance though some variation in the size of the upperwing spots occurs.
The female Dark Green Fritillary is highly variable in the appearance of its upper surfaces. Some individuals have an almost completely cream ground colour while variation in the extent of black markings also occurs. Many Irish specimens are referable to subspecies scotica.
The sight of a large bright orange butterfly engaged in a Herculean battle with powerful cliff-top gales is a memorable experience and is often the first encounter one has with a Dark Green Fritillary. The butterfly is extremely active which makes it difficult to observe for any length of time. Although it feeds from nectar sources especially favouring thistles [Cirsium ssp], knapweeds [Centaurea ssp] and Red Clover [Trifolium pratense] visits are momentary and involves the butterfly stabbing its proboscis frenetically into the bloom and fleeing to surge powerfully across the open expanses of its habitat. With an impressive display of grace and muscle it is tempting to regard this as a successful and resilient species but sadly this is proving not to be so. Our second largest fritillary inhabits a range of flower-rich habitats such as coastal areas where sand dunes, machair grassland and cliffs occur as well as cutaway bogs, limestone grassland, heaths, rough open hillsides and occasionally woodland clearings. The grassland habitat must be particularly rich in wild flowers including violets [[Viola ssp] the larval foodplant] and often contains some scrub and/or taller ranker vegetation such as coarse grasses and Bracken [Pteridium aquilinum]. In short a mosaic consisting of shorter and longer flower-rich turf preferably with some scattered scrub is required.
Unfortunately the flower-rich habitats the butterfly needs are in decline in Ireland. Coastal erosion along the east coast, over-grazing by sheep along the west coast, expansion of golf links, agricultural intensification and abandonment, removal of limestone pavement and the natural processes of scrub and woodland development on limestone and cutaways have caused declines in this and other species. According to the findings published in: Ireland Red List No.4-Butterflies. [National Parks and Wildlife Service, Department of the Environment, Heritage and Local Government, Ireland] a population reduction of greater than 30% in the past is suspected. With the decline in habitat quality set to continue further losses are expected. The species is classified as vulnerable in Ireland based on the IUCN [International Union for the Conservation of Nature] criterion that a population reduction of >30% is suspected to be met in the future as a result of decline in habitat quality.
Currently the stronghold of the species is around the coast where soils are thin, unfertilised and most likely to contain an abundance of native flora and some variation in sward height created by rough extensive grazing, natural erosion and human disturbance. The Burren region, North Sligo, Donegal and South Wexford hold strong populations but in many other areas populations are very low or have disappeared.
Why is this apparently robust creature so tied to flower-rich grasslands? Grassland species such as the Meadow Brown is partial to nectar and there is no evidence of a serious decline in the Meadow Brown. A clue to the restricted distribution of this fritillary lies in the requirements of the caterpillar.
The female deposits one or more ova on or in the vicinity of violet plants growing in bright situations under or close to scrub, Bracken or protruding from or growing up against a grass tussock. These hatch after two weeks or so and larvae hibernate without feeding on the foodplant. The following spring, in late March and early April the caterpillar begins feeding on the tender youngest violet leaves. On a site in The Burren I observed three larvae feeding close to each other but on separate plants. All the violets received full sunlight and faced south-east. The plants were located at the base of a Hazel plant [Corylus avellana] sheltered from the west by Hazel scrub. The proximity of limestone and the bare soil from which the plants sprouted created a warm micro-climate. Extensive cattle and horse grazing practiced here during winter and spring creates disturbance that allows for some open vegetation and germination of violet seedlings. The feeding behaviour observed may also provide a clue as to its special requirements. Young larvae feed by taking a few bites from the leaf edges [leaving diagnostic half-moon shaped leaf edges] and swiftly abandoning the leaf, hurriedly crawling down the stalk, moving to the adjoining leaf and repeating the process before departing the plant and hurrying away. Despite the appearance of purpose larvae soon stopped and remained motionless on the warm, bare soil for lengthy periods. [The ants and spiders present did not attack the larvae during the observation period but the hurried feeding might be related to the need to avoid predation. The final instar larvae were not as nervous in their feeding habits and spend longer periods feeding on a single leaf so that over half of a large leaf was devoured during the same feeding session. The larger size of the older larva presumably makes predation by small spiders less likely]. The time spent motionless in sunshine by young larvae indicates basking to digest food. At this early stage larvae studied ranged in length from 4mm-9mm and were covered in dark branching spines, possessed a prominent white dorsal stripe and golden lateral markings. The generally dark appearance helps heat absorption and concealment on dark soil with thin, mainly dry wispy vegetation. At this time of the year air temperatures are low so basking in warm, sunlit sheltered situations is important to young caterpillars. The larvae of all four fritillary species resident in Ireland bask but only in the Marsh Fritillary is this habit well known because its larvae bask communally in very open situations and this makes them conspicuous. While the Meadow Brown is able to thrive in uniform knee-high grassland that contains some nectar sources the Dark Green Fritillary needs a more varied grassland structure so its larvae can develop in the warmer micro-climate. These conditions seem to be met only in especially flower-rich grassland habitats that receive extensive or occasional light grazing and in scrubby grasslands similarly managed and with some scrub control. The loss/decline in quality of these habitats explains the Dark Green Fritillary’s decline.
Final instar larva on Common Dog Violet
The final instar caterpillar is a handsome creature livered in red and black. When fully-fed it draws loose vegetation together before forming a dark brown pupa inside this shelter. The pupa measures about 21mm and wriggles violently when disturbed and continues to do so some time after disturbance has ceased. Pupation occurs from about mid-May and lasts about 25 days. Emergence occurs from early June up to about mid-July. The flight period lasts from early June to late August but some individuals have been found in early September. The apparently strange insistence of the males in flying directly into powerful winds in the exposed areas it inhabits is explained by its search for a virgin female. Newly emerged females generally remain on the sward awaiting discovery by patrolling males. It is likely that unmated females release a pheromone so it makes sense for males to fly into the breeze. The mating ritual is brief but dramatic. The male mounts the open-winged female while flapping his wings over her. This is done to shower her with scent from his androconia [scales located mainly on the forewings of some male butterflies containing an aphrodisiac].He dismounts, stands at a right angle to the female and snaps his wings open and shut. He then walks around to her hindwings [the female’s wings remain open] and strikes the hindwings with his antennae. Finally, he stands parallel to her, bends his abdomen towards hers and the pair join. Mating is brief lasting only about 35 minutes. The female feeds for a few days before starting to lay her eggs while the male seeks a new mate.
Mating pair with the female on the left. Note the pristine appearance of the newly emerged female.
Another interesting feature of the Dark Green Fritillary is its communal roost. Typically at around 6pm in early July, the butterflies gather in tall grasses often with up to 8 individuals per square metre. Following preliminary basking the butterflies insinuate themselves deep into the grass tussocks where their greenish undersides and silver spangles that reflect the surrounding hues add to their blending ability. When the butterflies gather to roost an excellent opportunity arises to closely observe, admire and photograph this otherwise elusive icon of flower-rich wilderness. Article copyright © Jesmond Harding 2010.
What can Butterfly Conservation Ireland do to protect this butterfly?
We will continue to lobby NPWS for the implementation of light grazing management of habitats within reserves and national parks and to disseminate this and other conservation techniques to others whenever suitable means and opportunities occur. We are also directly involved in two site management projects to keep the habitat suitable and to create suitable habitat. The projects are based at Fahee North in Clare and at Lullybeg, County Kildare. We participated in the process of drawing up the Butterfly Red List which should inform conservation priorities on behalf of this magnificent butterfly.