WILDLIFE FACTFLIE: blue The Holly blue butterfly ( argiolus) is the first blue butterfly to emerge in early spring, March to May, with a second generation at the end of summer, July to September. The Holly blue is the most likely blue butterfly to be seen in gardens, woodlands, parks and churchyards. It flies high around bushes and trees while other grassland blue fly low to the ground. Holly blue butterfly caterpillars in the spring generation feed mainly on Holly, while the summer generation feeds on Ivy. Adult butterflies will visit a variety of sources for nectar such as Bramble, Holly and Forget-me-not. The adult male butterflies will also come down to the ground to get salts and minerals from damp mud and waste.

The Holly blue butterfly is bright blue with a 2.6 – 3.4cm wingspan and females have broad black edges to their wings. Summer generation females generally have broader black borders on their wings than the spring females. The underside of Holly blue butterfly wings is pale blue with black spots, while all other blue butterflies have orange spots.

The Holly blue butterfly is found across England, Wales and Northern Ireland but is mainly absent from Scotland. The population of this butterfly is on the increase and it is also spreading northward so it is not considered a conservation concern. The Holly blue is not threatened in Europe and is fully protected under the Northern Ireland 1985 Wildlife Order.

DID YOU KNOW? Photo credit: © Butterfly Conservation/Iain Leach Holly blue butterfly population fluctuate massively each year as they are parasitised by an ichneumon wasp which kills the caterpillars. As a result, the number of adults decreases the following year. This decreases the number of parasites, which allows the Holly blue populations to recover and the cycle starts all over again.