Whilst awaiting the installation of the bridge on Llyn Mawr, I was lucky enough to spot a bright yellow – male brimstone butterfly skipping between the knapweed.
Brimstones, whilst not threatened, are a somewhat elusive species, rarely sighted in the Garden and usually in spring. Like many species, they are closely linked to their food plants, and whilst the adults are not fussy, the caterpillars require buckthorn – usually alder buckthorn.
Brimstones are so named due to the sulphur yellow colour of the males, and may have been the original ‘Butter fly’.
A quick check of the records show only 2 alder buckthorn recorded on site, both on the site boundary.
Luckily, alder buckthorn is a part of our parkland planting mix, just for this very reason. A quick check in the tree tubes revealed some definite signs of caterpillar damage, although by now they will all be on the wing.
The increased planting of alder buckthorn within large scale planting schemes be paying off, with brimstones seeing the largest increase in recordings for 2018 in Wales, according to The UK Butterfly Monitoring Scheme, and an impressive 82% increase over 10 years.
So there we have it, we may now host a colony of Brimstone butterflies, so keep those eyes peeled.
Interestingly alder buckthorn was historically valued in charcoal making, producing a very fine gun powder. Its introduction into North America over 200 years ago has since led to it becoming an invasive species.
When it comes to conservation it is important that we know how these delicate ecosystems work, but its also vital that we take carful action where we can, not just for the attractive ones like the Brimstone, but also for the less photogenic species.
Oh and more good news, Devil’s Bit Scabious – a purple flowered plant which is the food plant of the rare Marsh Fritillary is also doing well on site, with large areas appearing at the top of Trawscoed meadow.