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We've had a report of a pristine male Chalkhill Blue on Devil's Dyke, Newmarket Thursday 2nd Oct. This came from the regular transect recorder. Not a species that I would have expected a second brood. Does anyone know of any previous examples?

Rob

Very interesting and a notable observation! The only reference I can find to 2nd brood Chalkhills is here:

http://www.biodiversitylibrary.org/item ... 8/mode/1up

Cheers,

- Pete

Memory serves me badly but I am certain I saw Chalkhill Blues in more than one October in the 1970s on Denbies Hillside, Surrey. I had thought it quite normal for late emerging stragglers (not second brood) to occur very late in fine season.

Jack

Thanks Gents.
Looks like both instances could refer to the legendary summer of 1976.

I know they've got a long emergence period and the Dyke has a huge population, but the past month's butterflies points to this being a second brood individual. We've had a full third brood of Wall Brown and partial second White Admiral.

cheers
Rob

In Switzerland chalkhill blues always fly into October and the species is considered exclusively monovoltine. In some years I still find it in November and have photographed individuals in good condition in the second half of October. If there were several records at Devil's Dyke after the species had been absent for some weeks it would certainly point to a second brood but I'm not sure any conclusion can be drawn from a single individual off the edge of the bell curve.

Guy

Fair comment, Guy, based on initial singleton.

I see that the transect walker has returned today, perhaps out of excitement and recorded 2 fresh males. I've checked the UKBMS table for the last couple of years and the normal count can run to the end of September, but I suspect that these would be worn females. The transect walker certainly thinks that 'something's up'.

I've had an email from the observer:
".... Last male seen on Aug 27 when I saw 26 butterflies. Two tatty females on Sep 3 then nothing until Sep 30 when I listed 1 tatty female. .... there was another recorder there yesterday from Northants who also saw the butterfly. "

Hi Rob/all,

This is an interesting observation. I think it is possible that highly atypical, late individuals sometimes arise as the result of another phenomenon, rather than representing additional broods, when the individual has gone through most of the next life-cycle (e.g. fourth brood Small Copper), or has emerged very early from a pupa which would normally over-winter (e.g. Duke of Burgundy).

Although we are increasingly seeing additional, partial broods in some species, these form a wider pattern of increasingly common sightings as climate change encourages some species to try out bivoltinism, or trivoltinism. These include Duke of Burgundy and White Admiral in the former category, and quite a number of species in the latter (Brown Argus, Small Blue, Holly Blue etc.).

In the case of Chalk Hill Blue, which usually overwinters as an egg, an additional brood would have to rely upon a far more remarkable sequence of events than the cases cited above, requiring the early stages to develop at significantly more than twice the normal pace, from an egg which is programmed to carry through winter. That’s a big ‘ask’.

However, we know that a percentage of pupae in some species (well documented in e.g. Orange Tip) are held over until the following year. This might occur more widely than we realise, and would represent a good system of spreading risk. I suspect that emergence from these particular pupae may occasionally be triggered by, for instance, an unusually warm and extended autumn.

I therefore think that it’s possible that these Chalk Hill Blues have emerged from pupae which were destined to hold back until next July/August, but have been ‘tricked’ into a life of solitude and misery by the weather. This might also explain the sighting of a male Chalk Hill Blue by my father and me on May 16th 2007, following record-breaking April temperatures. I believe this may have been omitted from the national database, on the basis of its extreme departure from the norm, but is documented by the ever-thorough Colin Pratt in ‘A Complete History of the Butterflies and Moths of Sussex’ (2011).

BWs, Neil

Hi Neil,
Yes, that makes sense. Must confess, I hadn't appreciated that Chalkhills overwintered in the egg. I did think that some very cold August nights followed by weeks of warmer weather could have triggered something, but any larvae would have had to progress at a phenomenal rate to reach the adult state in October.
Another similar example to your May Chalkhill would be the Oak Eggar moth larvae that over-winter twice in the North and emerge as adults earlier, in the spring rather than during July in the South.
All that said, I'm still intrigued by the article that Peter found - if someone has managed to do it in captivity with only 30 ova......Maybe only future climate change will give us the answer.
Cheers
Rob

I suppose the chances are that these individuals are indeed simply “late”, but as they are males (which tend to hatch early) and there seems to have been a reasonable gap between the previous butterflies disappearing and these ones hatching, could Rob’s original idea still be valid?…
Here’s a theory (albeit unlikely) which I’ve been thinking about since I heard about them. Probably bonkers (and maybe another word with one more letter beginning with the same two letters), but humour me for a short while….

Although Chalkhill Blues invariably overwinter as eggs, fully formed caterpillars are sitting inside these eggs over that period. (according to Jeremy Thomas’ “Butterflies of Britain and Ireland” they are fully formed, but remain within the eggshell until April the following year). If tiny caterpillars form inside the eggs reasonably quickly after they are laid, perhaps a vanishingly small percentage of these do not actually go into diapause, but carry on and hatch. This might be caused by the lack of an enzyme which would normally help to produce a protein necessary for them to commit to overwintering. A faulty gene could potentially be responsible. We all know of cases of pupae which hatch into adults if kept at elevated temperatures when they would normally stay dormant until the following year. Why could this not happen with an egg? The chances of finding one of the resulting caterpillars at “the wrong time of year” would be very small indeed and normally, all would die before reaching adulthood, so nobody would even suspect it. The first Chalkhill Blues seen on Devil’s Dyke this year were at the end of June and mating pairs were seen within a week or so of that date. Soon the Chalkhill Blue season kicked off in earnest and the numbers seen there exploded into the hundreds. The numbers of eggs which would have been laid must have been absolutely phenomenal this year. Even if only a tiny proportion of eggs hatched without overwintering, they might possibly have had chance to grow up (in the elevated temperatures of the summer - certainly faster than those hatching from the egg in April) and pupate in time to hatch by the beginning of October? Another of the Neil’s “risk-spreading” strategies? - this time eggs hatching early rather than pupae being held over for an extra year?

Alright… I’ll get my coat!

Trev

Saturday 25th October - 5-6 males and 1 female Chalkhill Blue reported on Devil's Dyke!

Just to point out, the Devil's Dyke in question is the one in Newmarket on the Cambs/Suffolk border.
It's SW-facing and the branch manage the grassland twice a year. This Sunday is the next work party, so we are hoping that the weather holds. It will be a bizarre feeling if we actually see one in early November!

Similar to elsewhere, we are continuing to get the odd report of fresh emergences of other species from urban areas, e.g. 3rd brood Holly Blues (Cambridge & Southend-on-Sea), and fresh, spiralling male Speckled Woods in East London.

regards,
Bertie