Silver Studded Blue Male
One blessing moving to Dorset, I get to see lots of these lovely little butterflies.
They can only be found in a small number locations in the UK and mainly on heathland.
They can typically be found in large colonies, up to hundreds in one location. Because they don't travel far I suppose is one reason they tend to be found in the same location every year.
Also these butterflies have a relationship with the more common woodland and black ant, when the females lays her eggs she will often do so near an ants nest, the butterflies caterpillar release a sweet secretion which the ants like and collect, so the ants will often take the butterflies eggs into their nest and protect them from other insect predators. Even when the butterfly emerges the ants will still cover them and protect them until they have dried out.