Scientific illustration involves learning about your subjects, as well as illustrating them. I've always been amazed by the blue butterflies (family Lycaenidae); partly because of their vivid hues; and equally because of their fascinating life-cycles and interractions with ants.
Most of the information in this blog comes from the website of Butterfly Conservation, a charity concerned with recording and researching British butterflies and moths, and preserving both them and their habitats. With the blues, as with many butterfly species; if you can get the right food plants, turf length, and habitat; then you can hope to sustain a healthy population of the butterflies too.
The Common Blue (Polyommatus icarus) is widespread across the Uk. It can be distinguished form other blues by its wing margins; white without black veins. As with most blues, the female is brown on top with orange markings toward the wing margins (in the background of my illustration below); she is sometimes confused with the very similar looking Brown argus butterfly (Aricia agestis) whose males and females are brown with orange wing margins.
Common Blue (Polyommatus icarus)
Eggs are laid singly on birds'-foot trefoil, and the caterpillars feed on the underside of the leaf. In their fourth (and last) instar, they become attractive to ants by emitting sounds as they pulse their head in and out of their body. Ants come and tend to them, protecting them and may even take them into their nests. They do the same for the pupa, which lie on the ground; looking after and sometimes burying them.
The blues are often very species specific in their food-plants; the Small blue (Cupido miniums) only feeds on kidney vetch; the Common blue on bird's-foot trefoil; and several species rely on Horseshoe vetch. The Holly blue (Celastina argiolus) has a more varied diet; switching from holly to ivy in the summer.
The Chalkhill blue (Polyommatus coridon) is much paler than its cousin species with milky blue wings and a black wing border. Its population is currently in decline, mostly due to habitat loss.
Chalkhill blue (Polyommatus coridon); detail of larger image
The one food plant of this butterfly is the horseshoe vetch.
It too has a close relationship with ants; in this case the Yellow meadow ant (Lasius flavus). It attracts the ant with secretions from its honey gland, and is then protected by the ant colony who bury the larvae (and thus help it escape predation).
Yellow meadow ant (Lasius flavus)
The Adonis blue (Polyommatus ballargus) lays eggs in short, grazed turf; caterpillars feed on horseshoe vetch. They produce sweet secretions form their "honey glands" to attract ants who protect them, burying them at night. The caterpillars overwinter, and pupate in the soil early in the spring, often within an ant nest. Although the Adonis will interract with many different ant species, they seem to like the red ants (Myrmica subleti) and black ants (Lasius alienus).
The Silver-studded blue (Plebeius argus) also relies on ants, and the females only lay eggs if they can detect pheremones from an ant colony (normally the black ant Lasius niger or, on chalkier habitats, L. alienus). The ants pick up the caterpillars soon after they hatch and take them to the ant hills where they're tended til emerging as adults by the ants. This species feeds on heather plants.
The Large blue (Maculinea arion) is our rarest blue butterfly, and easy to spot due to the large black spots on its forewing.
Large blue (Maculinea arion)
It lays eggs on the buds of wild thyme, and once the caterpillars have fed and grown to about 5mm long they drop to the ground, and wait to be found by red ants (M. subleti).
The larva attract them by producing sticky secretions from a "honey-gland". The ants carry the caterpillars to their nests, and this is where it becomes wonderfully macarbre.
The caterpillars feed on the grubs in the ant nest, overwintering, and hibernating til they emerge from their pupa in May; unable to spread their wings until they're free of the soil.
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