- Published on Tuesday, 06 August 2013 14:44
The Silver-studded Blue caterpillars are either brown or green, with a black stripe along the back. They hatch from their eggs in the spring and quickly form a close relationship with Black Ants. The ants take them into their nests and accompany them when they emerge from the nests to feed, mainly young heather shoots. The ants appear quite agitated as they attend the caterpillars, tap their bodies with their antennae. The caterpillar produces sugary fluids for the ants from a gland at the rear of its body, and the ants protect the caterpillar from being predated by spiders or parasitised by small wasps, which will try to inject their eggs into the caterpillar’s body. The caterpillar grows and sheds its skin four times, and these stages are called instars, until it is ready to pupate in an ants’ nest.
The adult butterfly emerges from its pupal case in an ants’ nest early on a warm morning by climbing a stem of vegetation by just a few centimetres, usually grass or heather. The butterfly will stay there motionless with its wings closed until it has dried out its wings and is ready to fly, and this can take around an hour. During this time it is vulnerable, so the ants continue to protect it and the butterfly continues to provide the ants with fluids, until the butterfly is ready to fly off and find a mate. It is believed that this is the only species of butterfly which has a continued association with ants during its emergence, making it the only butterfly that has a close relationship with ants in all four stages of its life – the females locate their eggs adjacent to ants’ nests, the caterpillars are attended by ants, they pupate in ants’ nests and the ants continue in attendance as they emerge as adult butterflies.
Silver-studded Blues form very dense colonies, and in most years several hundred can be seen at Prees Heath. Some only fly a few metres from where they emerged, and they can often be seen fluttering low over the heather in small groups or singly in search of a mate. Often this will be a group of males competing for the attentions of a female who may remain lower in the vegetation. Females will lay their eggs singly a few centimetres above the ground, usually on heather but they will also use other plants such as gorse, broom and bird’s-foot trefoil, bending their abdomen as they do this. The former airfield main runway which runs down the centre of the reserve is the best place to see the butterflies, and the further you walk along the runway from the southern end the more you tend to see. In cool or wet weather and in the evenings the butterflies form communal roosts in taller vegetation such as long grasses, mature heathers and willowherbs.