sanctuaryofwings
Dusky Large Blue (Phengaris nausithous), a species in the family Lycaenidae.
Photo: Didier Descouens · Wikimedia Commons · CC BY-SA

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Contents
  1. Identification
  2. Range and habitat
  3. Life cycle and host plants
  4. Behaviour and flight period
  5. Conservation
  6. Similar species

The Dusky large blue, Phengaris nausithous, is a blue butterfly of the family Lycaenidae, found across Europe and western Asia, including Armenia, Austria, Azerbaijan, Belarus, Bulgaria, the Czech Republic, France, Georgia, Germany, Hungary, Kazakhstan, Moldova, Montenegro, the Netherlands, Poland, Romania, Russia, Slovenia, Spain, Switzerland and Ukraine. It belongs to the same small genus as the Alcon blue and the Large blue, whose caterpillars spend most of their lives away from any plant, inside an ant nest.

Identification

On the upperside, males resemble the Scarce large blue, while the female is quite black-brown above. The underside is coffee-brown and bears only a single row of eyespots (ocelli). A reliable wingspan figure could not be confirmed from an openable source this run.

Range and habitat

The species lives in damp meadows, the same wetland grassland habitat that supports its host plant. Its life cycle is strongly tied to the herbaceous plant great burnet (Sanguisorba officinalis), so a meadow without that plant, however damp, cannot hold the butterfly.

Life cycle and host plants

Eggs are laid on great burnet, in the same way as the related Scarce large blue. The young caterpillar is pale at first, later turning purple-brown and finally probably yellowish-brown, and it feeds at first on the flowers of great burnet and later on the leaves. Its close relatives, the Alcon blue and the Large blue, are known to complete their development inside an ant nest, but no openable source confirms this stage, or the ant partner, for this particular species, so it is left unstated here.

Behaviour and flight period

Adults are on the wing in July and August, in Europe. The Dusky large blue has exactly the same habits as the Scarce large blue, with which it frequently flies together, and is usually still more plentiful than that species where the two occur.

Conservation

The IUCN category for this butterfly, given in the facts box, comes from its Wikidata record.

Similar species

  • Alcon blue (Phengaris alcon): a close relative with the same ant-nest life cycle, but on a different host plant, marsh gentian rather than great burnet.
  • Large blue (Phengaris arion): another relative in the genus, raised on wild thyme and a different host ant rather than great burnet.
  • Scarce large blue (Phengaris teleius): the species it most resembles and most often flies alongside, sharing the same habits in the same damp meadows.
  • Mountain Alcon blue (Phengaris rebeli): another close relative, tied to its own combination of host ant and food plant.

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