Challenge on Nature Photography Part 3

 

My third photo for the ‘Challenge on Nature Photography’ (sadly the last couple of days have been rather busy, so these photos haven’t been posted when they should have been), is of 2 Common Blues. It was taken in June this year, in an out-of-the –way spot on ‘the patch’, an excellent site for this species, with the great drifts of Bird’s Foot Trefoil that turn it into a yellow sea come May sustaining the many adults with their nectar, and the larvae with their leaves.

It’s heartening to be able to find good numbers of a butterfly for which the name ‘Uncommon Blue’ seems to be growing increasingly appropriate on the patch, after it reached an all-time population low in the washout summer of 2012, and despite showing signs of recovery in 2013 and 2014, is still by no means ‘common’. I’m a big believer in the field of dreams philosophy ‘If you build it they will come’, and, with the Common Blue’s precipitous declines in mind, I’ve tried ‘do my bit’ for this delicate creature, and grow its foodplant each winter to plant out in the garden, on an area of poor sandy soil created after some building works. The idea is that this will (when grown alongside other species of nectar-rich wildflower like Knapweed) provide breeding habitat for the roaming adults which occasionally end up in the garden, and shore up their populations locally.




A female Common Blue ovipositing in the garden.

So far it’s been a great success, with females putting in an almost daily appearance during August, and well over 50 eggs laid on the succulent, green carpets of foodplant that have resulted from my efforts. The efforts themselves have been fairly minimal, soaking the Bird’s Foot Trefoil seeds in October, planting them in normal garden soil the next day, watching them germinate about a week later, and then planting out the seedlings next spring, it’s easy and effective – I’d encourage anyone with (or indeed without) an interest in Butterflies to do the same!



A Common Blue ovum on Black Medick.

A final instar Common Blue larva.

Common Blue eggs are most often laid on short, nitrogen-rich growths of foodplant (the kind produced from grazing by rabbits, or seedlings), before hatching a week or so later to produce a small cream-coloured first instar larva. Growing, and passing through several more instars, it becomes greener, before forming a pale, sickly-green pupa from which the adult emerges after 2 or 3 weeks. Larvae from eggs laid in late summer will hibernate in leaf litter or grass, before resuming feeding again in the spring, and pupating in April.



A Common Blue pupa.

The adults often fly in fairly large colonies in suitable habitat, and are well-known for forming communal roosts; with discrete bunches fluttering like silvery flags in the breeze. The main benefit of this social approach to sleeping, is the phenomenon known as ‘Prey dilution’ – safety in numbers. Basically, if a marauding Robin comes along, an individual butterfly is less likely to be eaten as part of a group than when it roosts alone. It’s also thought that the actual number of attacks on butterflies roosting in groups is less than those alone, though this has been observed in Heliconids, a tropical family of aposematically-coloured species, where the spectacle of many butterflies with bright warning colours provides a more powerful repellent signal than a single individual – so perhaps can’t be applied to less bright, (and presumably delicious) Common Blues.

Habitat loss has sadly been the main driver in the decline of Common Blues, with Britain now having lost 98% of its wildflower meadows; it’s not hard to see why. This, compounded with a string of bad summers has been enough to set this species back significantly, but perhaps, in a warming climate this will be one of the few that benefits, with increased temperatures enabling increased activity and breeding success. It’s certainly a possibility, but could it also be tempted into the climate trap recently thought to have snared the Wall Brown? When, in warmer summers it attempts a doomed third brood that reduces numbers the following year - a possibility too. The future’s a mystery for the Common Blue, but let’s hope it’s a part of it.

 

References

1.       Finkbeiner S., D., et al. (2012). ‘The Benefit of being a social butterfly: communal roosting deters predation. Proceedings of the Royal Society B. 10(1098). Available at http://visiongene.bio.uci.edu/Adriana_Briscoe/Publications_files/Finkbeiner_rspb.2012.0203.full.pdf, [accessed 28/11/15].

2.       Barkham P. (2015). ‘Butterflywatch: Can the blues be in clover once more?’. Guardian [online]. Available at http://www.theguardian.com/environment/2015/aug/06/butterflywatch-barkham-common-blue-adonis-silver-studded-meadows-loss, [accessed 28/11/15].

3.       Van Dyck, H., et al. (2014). ‘The lost generation hypothesis: could climate change drive ectotherms into a developmental trap?’. Oikos. 10(1111). Avaliable at http://onlinelibrary.wiley.com/doi/10.1111/oik.02066/abstract, [accessed 28/11/15].