Holly Blue: variation in female markings between broods

[millerd]

There is a generally accepted clear difference in the degree of black marking between the first and second brood females in Holly Blues, the latter having markedly more black than the former. I have posted examples of third brood females over the last few years, and several people have asked me recently whether there is any noticeable difference between second and third brood examples. As a consequence I thought I would look at a selection from all three broods and see just what the extremes are. The periods shown for the broods are an approximation, between the first sighting (usually a male) until the last (usually a female).

First Brood: from the end of March until the end of June

2nd May

4th May

16th May

20th May

24th May

30th May

5th June

The last female seen from this brood was found laying on 30th June

30th June

As can be seen, these examples cover May to mid-June, though worn individuals were found for another couple of weeks. The first males from the second brood appeared about a fortnight later, in mid-July.

The next post will contain second brood examples, and the final one the third brood.

Dave

[millerd]

Second Brood: Mid-July to mid-September

11th August

17th August

17th August

17th August

17th August

17th August

17th August

21st August

24th August

5th September

Dave

[millerd]

Third Brood: October-November

9th October

10th October

22nd October

30th October

31st October

The last 2019 sighting (a male) was on 27th November. Here are some females from November in previous years for comparison in the absence of a 2019 November female.

16th November 2017

14th November 2018

Looking over the three broods it can be seen that within each there is quite a bit of variety (the various examples all seen on 17th August demonstrate this). Though the general rule remains true that the second has heavier black markings than the first, some of the first nearly approach the second in this respect. What can be seen however, is that the third brood females do not differ particularly from those of the second.

What actually determines the degree of black marking is difficult to pin down. The conditions under which the pupa develops are no doubt significant, but these will vary enormously with the only definite factor being that the spring emergence will have spent a relatively long time in cool conditions, and will undergo the period of the year when day-length increases markedly. The other two broods experience a shortening day, not much for the second but much greater for the third.

What it is that triggers the third brood itself, particularly those that appear right into November, is also mysterious. Days are very short, sunshine relatively weak even if the air isn't too cold, and there may even have been a few slight frosts. Why do some pupae not enter hibernation as the majority must?

I hope this has been an interesting study - even if it is not particularly conclusive, it may provide food for thought at least.

Dave

[Pete Eeles]

Excellent report, Dave!

the third brood females do not differ particularly from those of the second.

Thanks for the confirmation!

What actually determines the degree of black marking is difficult to pin down. The conditions under which the pupa develops are no doubt significant

My understanding is that the cells that contain the pigments are laid down shortly after the pupa has formed - some aberrations are artificially created by exposing them to extremes of temperature just after the pupa has formed. Since those formed at the end of the year will be in cooler temperatures (on average) than the offspring in the summer, then the environmental conditions (higher temperatures) may be the cause of the differences in colour.

I feel an experiment coming on

What it is that triggers the third brood itself, particularly those that appear right into November, is also mysterious.

With a 3rd brood becoming an increasingly frequent occurrence, and with second broods of other species more regularly appearing, it's almost certainly due to temperature I would suggest.

I hope this has been an interesting study - even if it is not particularly conclusive, it may provide food for thought at least.

One of the best this year

Cheers,

- Pete

[David M]

..Though the general rule remains true that the second has heavier black markings than the first, some of the first nearly approach the second in this respect. What can be seen however, is that the third brood females do not differ particularly from those of the second.

Thanks for this, Dave. Extremely interesting. I presume these findings are borne out on the continent where third brood Holly Blues are commonplace.

As you have found, the main distinction is between the spring brood and the first summer brood.

Perhaps time spent in the pupa plays a role?