Butterflies & moths to look for in April — Holly Blue Butterfly

Holly Blue Butterfly
Photo credit: Sue Smith

Where to look

A common garden visitor, also seen in parks, churchyards, hedgerows and woodland paths.


The Holly Blue (Celastrina argiolus) is the only blue butterfly regularly seen flying in gardens and city centres. It emerges well before other blue butterflies. and tends to fly high around bushes and trees where it gathers around Holly (in spring) and Ivy (in late summer) to lay its eggs. Once hatched, the caterpillars feed on the buds and flowers then drop to the ground to pupate (turn into chrysalis). Their wings are blue, but females have black wing edges.  The numbers of holly blues varies massively every year due to their relationship with a parasitic wasp (Listrodomus nycthemerus). The wasp injects a single egg into the living Holly Blue caterpillar. The wasp larvae will then feed on the caterpillar, eventually killing it after it has changed into a chrysalis. The wasp only feeds on Holly Blue caterpillars and some years will kill too many, leaving not enough for the next year, so the wasp numbers go down as well. This allows the butterfly numbers to increase again until the wasp numbers catch up and it starts all over again! 

For more info see https://butterfly-conservation.org/butterflies/holly-blue

Where we've found Holly Blue Butterflies

Holly Blue Butterfly spottings journal (9 seen)

Last seen Location Spotted by Group Notes
20 Apr 2021 Thornbury Golf Course Alex Foxmoor Primary Quite small, in amongst flowers
19 Apr 2021 Stroud Valleys Project
30 Apr 2020 Centre Stroud Trinity In our garden in the centre of Stroud
30 Apr 2020 St Briavels Izzy St John's on-the-Hill We have seen several holly blue butterflies a round the cow parsley in the field .
27 Apr 2020 Camborne garden Simon Camborne
15 Apr 2020 In our garden All of us! Buckley-Nolans Holly blue We love you
9 Apr 2020 Polzeath Daisy Blended This Holly Blue landed right next to my foot!
9 Apr 2020 Polzeath Gav Blended Lovely Holly blue female.
8 Apr 2020 Stroud Tamsin Stroud Valleys Project


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