From staring at fence posts to staring at the ground

Flanders Moss NNR

You might recall us peering at crusty old fenceposts in search of the Rannoch Brindled Beauty (Lycia lapponaria) moths back in April as part of our ongoing research into the species and it’s habitat preferences.

Well, for every successfully-mated female we found (which hasn’t since succumbed to predation or any other unfortunate ending) there must have been a batch or two of eggs laid on these aforementioned fence posts, as well as birch trees, the odd pine tree and bog myrtle shrubs.

The wingless female ready to lay her eggs in the craggy fence post using her long ovipositor.

As these eggs have hatched, the larvae will have sent out a silky string to catch the wind and parachute (or ‘balloon’) away, aiding their dispersal across the moss. (I’m aiming to witness this one day!)

I’ve been finding out where they have ‘ballooned’ to. This is easier said than done as there is no sure way of knowing how far they might have travelled. Although the caterpillars tend to wait until conditions are ideal, putting their lives in the hands of the Scottish wind and weather there is every chance that they could have flown too far! In which case they may have landed on the wrong habitat and starved. I now know some of them managed to in the right place, though…

Over the course of about 6 weeks, I’ve managed to find 48 caterpillars dotted across the reserve with the help of the NNR team and some generous volunteers. This may not sound like many, but considering how widely the larvae has probably dispersed, I reckon this ain’t too bad!

Caterpillar-hunting involves… well, looking all over the ground basically!

Excitement over the first caterpillar of the day! ©Katty Baird

Species with ‘ballooning’ caterpillars tend to have a wide variety of foodplants. Makes sense really, considering they don’t know where they might land!

With this in mind, we needed to keep an eye out for the larvae on pretty much any plant we came across. When surveying in the right habitat, this is easy-going enough as there will be plenty of heather (Calluna vulgaris), cross-leaved heath (Erica tetralix) and/or bog myrtle (Myrica gale) to focus on. However, we’ve been finding them on cotton-grass, birch, bog cranberry and one was even just sitting on a carpet of sphagnum!

An RBB larvae munching away on some cross-leaved heath (Erica tetralix) ©Katty Baird.

We even had a go at a night-time survey, having heard that caterpillars show up well in torchlight. We found one…so it was worth it! Very cool being on the moss at night, although I wouldn’t recommend doing this without an experienced bog wizard.

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These surveys will allow us to better understand Rannoch Brindled Beauty distribution as well as their habitat and foodplant preferences. We may also be able to understand how climate change could be affecting the populations and potentially other species.

They’re a pernickety species. I’ve found myself recognising ideal habitats and conditions that the larvae prefer. The not-too-dry, not-too-wet bog. Not-too-tall, not-too-short vegetation. Not-too-healthy-looking bog myrtle (yep, they really like the scrubby stuff). Not too sunny, not too cloudy, not too loud…

A patch of ‘ideal’ habitat for finding RBB larvae on Flanders. Short, scrubby bog myrtle with Calluna and Erica intermixed. The canes are where I’ve found larvae. Maybe they came from that birch tree?

It’s been an incredibly interesting project so far and, despite frustrations of not finding many (or any) where you think they’d be, it’s been very enjoyable as well. Slowing down to look at bog-specialist plants has allowed the whole team to see new things that would be otherwise overlooked, even those who’ve worked on Flanders Moss for years!

Thanks so much to everyone who has helped with the searches!

I will end with this video of the most active caterpillar of the whole search. If only they were all this conspicuous.