The holly and the ivy – and the holly blue butterfly
Aside from the Christmas carol, what brings holly and ivy together? Not just table decorations, but also a thoroughly festive butterfly
Yes, they might both be jostling for position in your homemade Christmas wreath. But did you know that both of these famously festive plants are also required by the holly blue butterfly, Celastrina argiolus?
Though ivy doesn’t feature in their common name, these delicate blue butterflies have a close relationship with both wintery evergreens. The prickly leaves of holly (Ilex aquifolium) are a must for this species in spring, whilst ivy (Hedera helix) is sought out in the summer.
By December, the UK population of holly blues are safely ensconced as chrysalises. This is the name given to the pupae of butterflies and moths – the hardened outer layer protects the soft developing insect within.
As the weather starts to warm, the butterflies begin to emerge. They are seen from early spring onwards; fluttering over gardens, hedgerows and woodland pathways in search of holly. Though holly blues prefer to lay eggs on female holly plants, you can often find them on male plants too.
The holly blue on ivy (Hedera helix)
This relationship leads to a boom-and-bust rhythm for the holly blue, in which the butterfly’s populations follow a four-yearly cycle. As numbers of the parasitoid wasp increase, the holly blue population suffers; resulting in a crash in wasp numbers the following year, since they have few hosts left. The holly blues then have a couple of years to recover before wasp populations build up enough to again have a large impact.
The holly blue on its namesake plant (Ilex aquifolium)
Not only does ivy support the holly blue, but it is a fantastic plant for wildlife in general. It provides cover for nesting birds, habitat for invertebrates, and is a valuable late-season pollen source for many pollinators, particularly the ivy bee. Recent RHS research highlighted just how much biodiversity can be supported by growing ivy up a wall – which also helps to keep houses cool in summer and reduces damp, too.
Fancy spotting the holly blue in your garden? Plant a couple of these top 10 AGM-winning hollies and ivies to give not just butterflies, but also birds, bees and other wildlife a helping hand.
