Holly Blues, Celastrina argiolus, in East Lothian

I have mentioned the Holly Blue in many of my annual round-ups, but think it deserves a post of its own!

Since I started collating the butterfly records for East Lothian in 2007 there has been the odd record each year of a Holly Blue. When I was working as a Countryside Ranger in the late ‘90s there was an established colony of Holly Blues on the western boundary of East Lothian at Newhailes and Brunstane. They were more or less unheard of anywhere else in Scotland at the time and there was a bit of suspicion about how they had arrived there.

Despite the knowledge that they were regularly seen in the Newhailes/Brunstane area there are surprisingly few records for Holly Blues in that area.

Over the next few years I received records of one or two Holly Blues each year. These were mostly from coastal towns in the north of the county. In the spring of 2011 there was great excitement when I spotted three Holly Blues on a Holly bush in Aberlady. Unfortunately, there were no records of a second generation that summer, or any subsequent records from that site.

By 2013 the Newhailes colony appeared to have died out and I feared that two poor summers in a row had wiped out Holly Blues in East Lothian. However, I received one record in 2014, 2015 and 2016 from those towns in the north of the county, leading me to believe that somewhere in that area was a little colony, possibly in a large private garden.

Then in 2017 and 2018 I didn’t receive any records. But, in 2019 there was great excitement on Facebook, as someone had found a number of Holly Blues outside a garden on the edge of a golf course in Gullane. Later in the year they were also regularly spotted in two other locations in the village. That year I received 28 Holly Blue records.

The excitement grew the following year when Holly Blues were spotted in various villages about 8 miles away from Gullane. By the end of 2020 I had received records of 90 Holly Blue being seen.

In 2021 the expansion of the range and population continued, with Holly Blues being quite regularly spotted and reported to me. Again they had advance by about 8 miles  following old railway walks and river valleys.  By the end of the year I had received records of 101 Holly Blues.

And in 2022 the trend continued with 288 Holly Blues being reported to me from much of the county. By this time they had spread to Edinburgh and there were some sightings in the Scottish Borders.

Already this year they have spread further across the county and a good number have been seen in the Borders, Edinburgh and Midlothian. I can't believe that this little butterfly has managed to colonise the entire county in just four years!

The Holly Blue has two generations a year. The first being seen in April and May and the summer generation flying in late July and August. We have also seen the odd Holly Blue in October and November, as a very small third generation. During their flight periods it is worth checking any sunny patches of ivy or holly for these little silvery-blue butterflies.

In England the populations of Holly Blues fluctuate considerably over a five year cycle. This is because of a parasitic wasp, Listrodomus nycthemerus, for which the Holly Blue is its only host. The population of Holly Blues can be decimated, but the following year the wasp has very few hosts causing a drop in its own numbers. As the Holly Blues continues to extend its range in Scotland it will eventually join up with the English population and, possibly, the parasitic wasp!