2nd brood Marsh Fritillaries?

[petesmith]

Up until a few days ago, I had thought that the Marsh Fritillary was strictly single-brooded, with the larvae being obligate hibernators on entering the fourth instar. I also thought that it was univoltine, not just in the UK, but across Europe as a whole. All the books say so, or so I thought.

I was very surprised therefore when reports started coming through of a few adult Marsh Fritillaries on the wing in central Lincolnshire last Friday.

Today I went out to look for myself, and took the photographs below:

E.aurinia - 2nd September 2019 - Lincolnshire Limewoods

A little more digging, and I found this in "La Vie des Papillons" by Lafranchis, Jutzeler, Guillosson, Kan & Kan :
"De rares chenilles grandissent plus vite et atteignent le derniere estade en fin d'été. Elles se nymphosent pour produire d'exceptionelles émergences d'imagos de seconde génération en Septembre."
(translation: Rare caterpillars grow more quickly and reach the final stage at the end of summer. They pupate to produce exceptional emergences of second generation adults in September.)

Is this a case of a 2nd generation in Lincolnshire this year?

There is an alternative possibility that the adults currently on the wing (and there are only a few so far) are the result of delayed larval development from earlier this year.

This particular colony has experienced a massive population explosion over the past two years, to such extent that many thousands of larvae left the main breeding area to move into surrounding woods this spring. Some successfully completed their development on honeysuckle; many hundreds perished. During the main flight period (early May-June-early July) many thousands of adults were on the wing, but at the same time it was possible to still find small, post-hibernation-sized larvae. At one point in early April, the Devil's-bit Scabious had been almost entirely stripped across large parts of the site, and at least one group of 4th instar larvae was found later in early summer, having apparently gone back into diapause. For several weeks in late June one could find pupae, adults, eggs, 1st, 2nd, 4th, 5th and 6th instar larvae simultaneously.

My question to the collective wisdom embodied within this group is this: does anyone have any experience of putative 2nd brood Marsh Fritillaries, either in the UK or in Europe? Does anyone have any comments or theories as to why in early September it is currently possible to find adult Marsh Fritillaries at nectar on the larval foodplant (photographs such as those above are a complete novelty to me! I would have previously deemed them fake...) here in central Lincs? Or indeed has anyone experienced 2nd broods of this species in captivity?

All theories and thoughts welcome!

[David M]

Up until a few days ago, I had thought that the Marsh Fritillary was strictly single-brooded...

Me too, but clearly they aren't, as your images prove.

I think both of those theories are plausible, and certainly if ever there was a time for it to happen then this year in Lincolnshire is it.

From what I've read, there were extraordinary numbers during the normal flight period, and this may have contributed to slight changes in the pattern of phenology, leading to an 'exceptionally rare' second emergence of adults.

Well done with the observations (as ever), Pete, and thanks for sharing the information.

Food for thought.

PS - I presume that's the foodplant they're nectaring on?

[petesmith]

Hi David,

Agreed - this year was always going to be exceptional for them!

And yes - it is Devil's-bit Scabious that they are pictured on - the plants recovered incredibly well from almost total annihilation in early spring. Quite amazing.

Next year could be even more interesting as we currently have a meadow covered in larval webs...

[Chris Jackson]

.... My question to the collective wisdom embodied within this group is this: does anyone have any experience of putative 2nd brood Marsh Fritillaries, either in the UK or in Europe? ....

Hi All,

Regarding putative 2nd brood Marsh Fritillaries, in Europe, here below is a link to the south of France PACA sightings for E. aurinia (PACA = the 6 south-eastern 'counties' of France):

https://www.faune-paca.org/index.php?m_ ... =sp&y=2019

You can switch from one year to another by clicking on [2019], [2018] etc.
There are a couple of years where the sightings seem to show some late emergers, a month or so after the majority of adults have stopped flying. These charts do not differentiate between altitudes, however.

Cheers,
Chris

[petesmith]

Thanks for that Chris - interesting additional data to consider.
As you say, a shame that there is no differentiation regarding altitude, given the occurrence of this species at high altitude in the Alps.

[bugboy]

I think it's worth noting that there don't seem to be any reports of second brood Marshies anywhere else so my gut feeling points to some late developing larvae rather than a true second brood due to the massive population explosion.

[MrSp0ck]

It seems that the Glanville, Heath and Marsh Frits did all produce small Second Broods this summer, probably due to the weather in February, July and warm spells inbetween.