Brighton Blues Festival (Part 5) 13.9.20
Sunday morning proved to be 'business as usual' at Whitehawk Hill, but in the early afternoon, after the majority of visitors had dissipated, the butterfly action stepped up a couple of gears; there had been a major emergence of Long-tailed Blues that morning and they were now taking to the air. By mid-afternoon there were at least 20 individuals (probably 25) flying, including a significant number of virgin females, which were relentlessly hunted down by fresh, Sussex-born males.
Over just a couple of hours, in just one small area, three courtships and pairings were observed. I suspect that plenty more went unnoticed; it was difficult enough to observe and record what was going on with these amorous couples, much of it simultaneously.
The pattern of courtship that Max Anderson and I observed on 9 September (between a late wave immigrant male and Sussex-born female) was repeated on each occasion (this time between exclusively Sussex-born insects), with the females playing 'hard to get' and at first seeming to vigorously reject the male's advances. The females fly away from the males, in short 'hops', then flutter their wings rapidly while dropping deep into undergrowth, or apparently trying to hide below leaves. The males must pursue them with equal vigour and it takes several attempts for the male to latch onto the female with his oversized claspers. It is tempting to suggest that this ritual is designed to test the male's reproductive 'fitness'.
Mating occurs for approximately 45 minutes in the heat, but may last for two hours (or more) if the weather cools significantly. When the female does decide to uncouple, the process appears difficult to achieve (those claspers are strong!). There is much fidgeting, kicking and wing-quivering by the female, and she often takes short flights with the male in-tow, until separation is achieved.
It is interesting to observe what then happens to the females, which immediately begin a phase of frenetic nectaring. These individuals are often seen doing the same, the following morning, but, assuming reasonable weather, they are then never seen/photographed again. The females apparently disappear from the site around, or soon after, midday. Whereas the UK-born males will hang around, and behave in a colonial manner, gradually deteriorating in condition, the females will not. This is the pattern I've observed consistently over the eight years I've been studying the Long-tailed Blue on British soil (across Sussex and Kent).
This is one of the many lines of evidence for reverse migration in the species, much of which is summarised in
The Butterflies of Sussex (pp. 261-265). Another, of course, is that these females do not lay any eggs on the BLEP plants in Britain, which are now dying off and won't be of any further use to the LTB, at least until the fresh buds and flowers are available to the next wave of migrants in August (occasionally late July) of the following year.
What with climate change happening how much longer would you guesstimate before the LTB is a permanent species in the UK? They seem to have set up a pattern of migrating here and conditions can't be too dissimilar now to what they experience on the continent so I'm assuming (and I know that's a dangerous thing to do 
)that eventually our winters will reach a similar meteorological 'standard' as where they're currently found on the continent and so they will be able to survive the winter?
