Holly Blue – Celastrina argiolus

Featured image: Holly Blue ([1] @Trevor)
  • Class: Insecta
  • Order: Lepidoptera
  • Family: Lycaenidae
  • Subfamily: Polyommatinae
  • Genus: Celastrina
  • Species: argiolus

Conservation status: No concern

 

 

 

Appearance:

  • Wingspan: 26-34mm [1]
  • Sexual dimorphism: Yes. Female forewings contain broad black borders not seen in the males
  • Wing Shape: Smooth round edges
  • Dorsal Wing: Bright blue with black edges. Small White fringe.
  • Ventral Wing: Pale blue with black spots
  • Body: Blue body, antennae have black tips
Male Holly Blue ([1] @Nick B)
Male Holly Blue ventral surface ([1] @Clive)
Female Holly Blue ([1] @Neil Freeman)
Female Holly Blue ventral surface ([1] @Mark Colvin)

The presence of the blacks spots on the underside of the wings is a useful way to distinguish this species from the Common Blue.

Distribution:

holly-blue-distribution
Holly Blue distribution across Britain from 2010-2014 [3]

The Holly Blue has a very widespread distribution across the world including, temperate Europe, North America, North Africa and Asia [2]. Within Britain, the Holly Blue is confined to Southern England and Wales with little record of its presence in Scotland [1].

Suitable habitats include Gardens, Parks, woodlands and anywhere else their food plants can be found [1,2]

The populations fluctuate largely in a few years cycle due to the impact of the parasitic wasp (Listrodomus nycthemerus) has on its life cycle [1,2]. The wasps lay their eggs directly into the Caterpillars and then adult wasps emerge whilst the Holly Blue is in its pupal form, Killing the individual [1].

Life Cycle:

The Holly Blue undergoes two broods each year. In more northern species there may only be one brood [1]. The main larval food plants are Holly (Ilex spp.) and Ivy (Hedera helix) [1,2]. Bramble, dogwoods, gorses and snowberries are also used [1].

Butterfly:

  • Overwintering pupa butterflies emerge in April
  • Non-overwintering butterflies emerge in late July/Early August

Eggs: The white eggs are laid singularly at the base of unopened flower buds [1]. The first brood is known to lay its eggs upon Holly plants and the second brood uses Ivy plants [1]. The eggs will hatch after two weeks.

  • First brood are laid in May
  • Second brood are laid in August

Caterpillar: The caterpillar is plain green and very camouflaged. To feed they will bore a hole into the flower bud and scoop out the contents from inside [1]. The caterpillars are vulnerable to the parasitoid wasps and in some years, the number of wasps is higher which greatly influences the amount of caterpillars that are affected reducing the population of butterflies [2]. The caterpillar stage lasts for 3-4 weeks [1].

  • First brood caterpillars hatch from May to early June
  • Second brood caterpillars hatch from August to early September

Pupa: The pupa forms and either on or near to the ground [1]. They have a relationship with ants whereby the pupa secretes nutrients to feed the ants and in turn the ants protect the pupa from predators [4].

  • First brood pupa form in July and last for 2-3 weeks.
  • Second brood pupa form in September and hibernate during winter, reawakening in Spring.
Holly Blue egg ([1] @Pete Eeles)
Holly Blue caterpillar ([1] @Pete Eeles)
Holly Blue pupa ([1] @Coopera)

 Behaviour:

The Holly blue is not shy and can be approached closely [4]. They are seen flying high off the ground which is a characteristic not seen amongst other blue species [1].

They prefer to feed upon the honeydew/sap of plants rather than the nectar in the flowers [1]. They primarily feed on Sap, Bramble, Bugle, Buttercups, Forget-me-not, Holly, Ivy and privet [1,2]

When feeding they keep their wings closed but in early mornings they can be seen basking in the sun with their wings held slightly open [2].

Holly Blue in Northumberland:

holly-blue-2015
2015 Sightings across the Northeast [7]

North East England Status: Uncommon resident [5]

The Holly blue has not been recorded from Northumberland [6]. In woodlands with holly and ivy the climate in Northumberland is not warm enough to support populations [6]. However since this book was published there has been a steady change in climate and the Holly Blue has spread north which means that there may be more sightings in the near future [1].

2013 and 2014 were disappointing years for Holly Blues with only 56 and 45 butterflies sighted respectively [7]. 2015 saw an increase with 101 individual sightings in the Northeast [7]. However the numbers in the Northeast have been increasing, in 2001 and 2002 there was a combined sighting of only 4 individuals [7].

Most of the 2015 sightings came from within Newcastle Upon Tyne with the furthest north sighting being made in East Holywell near Whitley Bay on the coast [7].

References:

[1]  UK Butterflies (2017) Holly Blue http://www.ukbutterflies.co.uk/species.php?species=argiolus Accessed 13 February 2017

[2] Learn About Butterflies (2017) Celastrina argiolus http://www.learnaboutbutterflies.com/Britain%20-%20Celastrina%20argiolus.htm Accessed 13 February 2017

[3] Butterfly Conservation (2017) Holly Blue http://butterfly-conservation.org/50-923/holly-blue.html Accessed 25 February 2017

[4] Hammersley D (2003) A butterfly notebook. The book guild ltd. East Sussex

[5] North East Butterflies (2017) Butterfly Species http://www.northeast-butterflies.org.uk/speciesb/butterflies.html Accessed 13 February 2017

[6] Cook NJ (1990) An atlas of the butterflies of Northumberland and Durham. Northumberland biological records centre, the Hancock museum. Newcastle Upon Tyne

[7] Fleming S, Waller I, Perkins M, Norman R, Dover, Donnelly A (2015) Butterfly summary 2015. Northeast England branch. Butterfly Conservation. http://www.northeast-butterflies.org.uk/download_files/2015ButterflyReport.pdf Accessed 25 February 2017