Plan B(ee)

July found me in the Outer Hebrides, hoping to get out to the islands of St Kilda for 3 or 4 days.  This is always a chancy endeavour: easterly winds can make a landing impossible, and the tour operators do not risk the fifty-mile journey out into the Atlantic from Harris when the sea is too rough, whatever the wind direction.  Since I wanted to spend a few days on St Kilda watching the feral Soay sheep, my travel plans had to have quite a bit of contingency built in.  All the tours run as day-trips, and there are no fixed sailing dates, instead you book a two-day window and have to be poised and waiting the day before your window to see if your trip will go ahead, and if so, on which day.  If you want to stay overnight on the island then of course you have to book two two-day windows with no certainty that either will be feasible.

‘Make sure you bring enough food for a fortnight’, said Seamas, owner of the Sea Harris tour company, ‘In case the weather sets in and we can’t get back for a while.’

Prospects seemed poor, to say the least, when I reached Harris and made contact with Seamas.  A settled spell of weather was just coming to an end, and the forecast (correct as it turned out) was for brisk easterlies.  Sailing during my first two-day window was out of the question, and the second one was looking highly unlikely as well.  Seamas might be able to get me out the following week, but that would mean extending my holiday and neglecting family responsibilities so I resigned myself to giving Kilda a miss this year and having another go in 2018.

Hebridean Blues – spot the kite surfer!

However while Soay sheep were the main purpose of my trip, there are plenty of other good reasons for visiting the Outer Hebrides.  So I did not despair, I turned to Plan B.

There is a type of wildflower-rich grassland found only on the Atlantic seaboard of Ireland and North-west Britain.  This is known as machair, and it is at its finest and most extensive in the Outer Hebrides on Harris and the Uists, and at its most colourful in June and July.  I love wildflowers en masse, and although I had been to the Outer Hebrides several times before I had somehow never manged to coincide in place and time with the machair in bloom.  Bumblebees are a more recent interest of mine, and as well as its floral interest the machair has become the last refuge in Britain and Ireland for the Great Yellow Bumblebee (Bombus distinguendus).  Plan B(ee) was therefore to get to know the machair better and to find Great Yellow Bumblebees.

The cool, wet and windy weather on Harris did not make for an encouraging start, and it wasn’t until my third day there that I laid eyes on any bumblebee at all.  This was not a Great Yellow, but it was an exciting one.  I was on the closely grazed turf of the machair at the foot of Glen Cravadale, admiring the combination of flowering thyme on the ridges of the old lazy beds (ridge and furrow grassland) with daisies in the furrows and an abundance of bog pimpernel (Anagallis tenella) in the wettest patches, when in a lull between showers there was a loud buzz and a bright ginger bumble whizzed past me.  ‘Surely not a tree bumble!’ I thought.  Tree bumblebees (Bombus hypnorum) are a recent addition to the British insect fauna which, having first crossed the English Channel in 2001 are ‘doing a collared dove’ and spreading rapidly northwards.  They are on a roll, and I knew they had already reached the Central Belt of Scotland, but surely they couldn’t have already made it this far. (In fact, I met a fellow bumblebee enthusiast, Ptolemy McKinnon, on the Farne Islands in August and he told me he had seen them in Perthshire earlier this year; and when I checked online later, I discovered that they have even been recorded from the Isle of Mull, so it is certainly not beyond the bounds of possibility that they will make it to the Outer Hebrides within the next few years.)

That was the only bumblebee I saw that day, but the following one held far more promise – breezy, but bright sunshine – and I spent the afternoon on the machair at Northton.  This was much less heavily grazed – a pointilliste carpet mostly of white clover and yellow buttercups.  Machair is notable for the profusion of common grassland flowers rather than for rare plants, but despite the sunshine and the flowers it took quite a while to catch up with the bumbles.  I kept hearing buzzing and zooming noises behind me but by the time I had turned around the buzzers and zoomers had disappeared.  It was as frustrating as it would have been had I tried to spot a corncrake, two of which were scritching away in the marshy grassland down towards the shore.  Finally I got my eye in and started seeing bumbles – most were like the previous day’s ginger beauties, and in the sunshine it was easy to see that they were not tree bumbles, their abdomens being a very pale fawn above and black below – a combination that on a bee glanced in flight does resemble the white-tipped black abdomen of a tree bumble.  These however were Moss Carders (Bombus muscorum) a species I had not, to the best of my knowledge, seen before.  On the mainland Moss Carders look pretty similar to Common Carders (Bombus pascuorum), but out here on the western seaboard they are so bright that some consider them a separate subspecies.  The reason that, despite this, they were hard to spot lay in their foraging technique.  They were all feeding on white clover (Trifolium repens), and mostly staying on the undersides of the flowerheads, and keeping low when moving between the flowers.  When they did break cover, they did so at speed and usually shot off out of sight, whether in search of a fresh clump of flowers or heading back to their nests I do not know.  They were not particularly numerous, but outnumbered the White-tailed Bumblebees that were also feeding on the white clover.  White-tailed Bumblebees are a bit like Whiskered Bats in that the more closely they are studied the more it is realised that they are actually a complex of several species that look very similar to one another, and which it is certainly well beyond the competence of a novice to separate.  I did find a definitely different bumblebee with a white tail though.  This was a Gypsy Cuckoo Bee (Bombus bohemicus) a brood parasite, and rather than feeding it was hunting for the underground nests of white-tailed bumbles into which to sneak and lay its eggs.  It was exploring a rabbit warren, flying from hole to hole and disappearing into each for a minute or so before re-emerging to carry on its search.  However I saw no Great Yellow Bumblebees.

Machair at Northton, Harris

My next bumbling opportunity was two days later on North Uist at the RSPB’s Balranald Nature Reserve on a cool, grey afternoon.  The machair here was different again – a much lusher mix dominated by white and red clovers with lots of ragwort (Senecio jacobaea).  There were few bumblebees about, again mostly Moss Carders with a smattering of White-tailed Bumbles.  They were concentrating on the red clover (Trifolium pratense), but one Moss Carder at least was having a frustrating time.  It was a particularly small worker and drew my attention because of its frantic high-pitched buzzing.  Courtesy of my close-focussing Pentax Papilio binoculars I could see that it was in difficulty.  It had its face thrust firmly into the corolla of a red clover floret but was gripping on only with its front pair of legs.  The middle and hind pair were waving wildly as it attempted to reach the nectar within.  I presume it failed, for after a while it moved on and switched its attention to the, considerably smaller, white clover flowers.

Finally, just as I was about to give up in the failing light, I spotted a pale yellow bee on red clover – largish, but not especially so and hence something of an anti-climax, but nonetheless a Great Yellow.  It gave me the slip before I could get a photo.

Machair at Balranald, North Uist – ragwort and red clover

My final bumbling session was on the island of Berneray several days later (I did manage to get to [bee-less] St Kilda after all), still breezy, but dry and with patches of sunshine.  The machair here was wonderfully varied with colourful strips of weed-infested arable crops as well as clover-dominated ungrazed pasture and abutting grazed pasture, dune slacks and marsh.  There was a good variety of bumbles including White-tailed Bumblebees and the final two Outer Hebridean species – the Garden Bumblebee (Bombus hortorum) and the Heath Bumblebee (Bombus jonellus).  I only saw one Heath Bumble and it was feeding on Red Bartsia (Odontites vernus) while all the other bees were focussing on red clover.  As with everywhere else I had been, the Moss Carders were far and away the commonest species, outnumbering all the others put together.

Machair on Bernerary
Moss Carder on Red Clover
Corn Marigolds, Berneray
Red Clover – the quintessential machair flower

The weather took a turn for the worse after this and I was harried off the islands in wind and rain with no further opportunity to look for any more of the elusive Great Yellows.  This is, I gather, a not unusual experience for seekers of this species – they are very thin on the ground, only forage during sunny weather and have a very short active period during their life cycle.  Queens do not generally emerge until mid-June, and produce only a small number of workers.  The daughter queens (princesses?) and drones are on the wing in August, and by mid-September these new queens are all mated and tucked up in their hibernation sites, and everyone else is dead.

I wondered if this pattern of life cycle might be an adaptation to the short summers of high latitudes, but a bit of internet research indicates that this is not the case.  Although the distribution of Great Yellow Bumblebees does extend quite far north, they are found all across the mid-latitudes of Eurasia and are definitely not one of the subarctic specialists.  Rather they are grassland specialists, timing their activity cycle to coincide with the peak flowering season of the red clover and other legumes.  As such they are in Britain and Ireland confined to areas with extensive, traditionally farmed wildflower-rich grasslands.  Like the corncrake that still lives alongside them they were formerly widespread but have been driven to the fringes of the far north and west by the relentless deflowering of farmed grasslands consequent on agricultural intensification.  The climate on the machair may be less than ideal for them, but this is the only habitat left in the British Isles where their preferred flowers still bloom in abundance over wide areas so here they persist, hanging on by the tips of their tarsi.

Moss Carder on Kidney Vetch (Anthyllis vulneraria)

The story is somewhat different for the Moss Carders.  These rufty-tufty bees seem to be real specialists in damp, cool open habitats and it is surely their ability to cope with the rain and the wind that gives them the edge over all the other bumblebees in the Hebrides and makes them, rather than the Great Yellow, the quintessential machair bee.