Living on the National Trust’s Great Chalfield Estate gives me some interesting opportunities when it comes to looking for wildlife in the grassland/unimproved pasture/’wildlife-friendly’ farmland habitats that are so carefully and lovingly looked after here. After two and a half years of looking I’m not likely to find many new birds now (though Turtle Dove and Cuckoo are two obvious – and concerning – gaps on the GC list), but I am finding species from other groups that I know virtually nothing about. Which is fascinating.
It’s also a little bit humbling to think that I’ve been calling myself a ‘semi-naturalist’ for years whilst only knowing birds, southern butterflies and macro-moths, and the commoner dragonflies, but not having much of a clue at all about trees, arable plants, hoverflies, bees, shieldbugs, spiders, weevils or longhorn beetles – all things which I wish now I had bothered with decades ago. It’s never too late to learn though, and – as I said – living on a National Trust estate is giving me opportunities aplenty to discover what’s been under my nose all the time I’ve been out birding.
Large Bee-fly Bombylius major, Great Chalfield, April
Which brings me to Large and Dotted Bee-flies Bombylius major and B. discolor, flies that flick their eggs into the burrows of solitary bees where they hatch and apparently set about parasitising the larvae of the host bee species. I’m more than happy to admit right from the outset that while I had heard of Large Bee-fly (and perhaps come across as quite knowledgeable about it due to the elliptical style that blogging and Twitter encourage) I’d never seen one before I moved to Great Chalfield. They are, it turns out, not scarce, favour Primroses, and are so common this year that even the Daily Mail (which seems to be focussing ever more tightly on the Kardashians, the curvier TOWIE-ites, someone called Danielle Lloyd and similar major world-figures) ran an article on them, though labelling them ‘One inch monsters’ once again made it obvious that the UK media between them have barely a single naturalist on their combined staffs. Hey ho…
Large Bee-fly Bombylius major, Great Chalfield, March
The Dotted Bee-fly, however, was completely new to me until a few weeks ago. Similar to the Large Bee-fly but with dotted wings rather than dark-edged ones and dark hairs on the tip of the abdomen (which are surprisingly easy to see even in flight, when they have notably dark ‘rear ends’ unlike major), it’s a far rarer insect that is categorised as Nationally Scarce and until a few years ago was the subject of a UK Biodiversity Action Plan after a population crash in the 1960s and 1970s that correlated with a crash in solitary bees.
As I say, I knew nothing whatsoever about B. discolor until the end of March this year when a message appeared on the Bristol Wildlife Yahoo listerve. The observer talked about Dotted Bee-flies and asked how common they were in the region. Steve Covey, Wiltshire’s Odonata recorder and an excellent all-round naturalist, replied that “around Swindon and Wiltshire generally they are reasonably frequent. I have seen them at Morgan’s Hill, Devizes and my back garden in Swindon so far this year and they are widespread on Salisbury Plain“.
Now, if I look carefully enough I can make out the ridge of Morgan’s Hill Nature Reserve from Great Chalfield; Swindon is just 15 miles down the M4; and we can sometimes hear artillery fire rolling up from Salisbury Plain when the wind is in the right direction. The Dotted Bee-fly, according to various sites, favours unimproved pastureland with Ground-Ivy (common here) and colonies of (especially) Andrena flavipes which burrow into eg the soils of sparsely vegetated field margins – both of which we have here. It seemed likely, therefore that a Nationally Scarce insect would be here if I looked for it.
Obviously I found it, or I couldn’t have posted the photographs above. It was a very satisfying moment of course, but it does beg a question: just how scarce is the Dotted Bee-fly really? I would stake everything I own on there being very few people in Britain who have been looking for Dotted Bee-flies since the population crashed four decades ago. Professional entomologists are rarer than most Bee-fly species in the UK, and while the internet does now provide quite a bit of data on them you’d have to be looking for that info to find it and to want to know about discolor to actually absorb it. Is it therefore a species that could be more common than previously thought? With the caveat that ‘old-style’ intensive farming has meant the loss of plants, unimproved pasture, and host bee colonies, surely it is more widespread than currently suggested by the records (along with a host of other poorly-studied insects, plants, and fungi).
All of which led me to a question that I put out on Twitter and that (so far anyway) hasn’t been answered. Is there, I asked, a term used by ecologists which describes the revision that may need to take place when a previously rare or scarce but little-known species is discovered to be much commoner SOLELY because observers became familiar with it and went looking for it (as I did with the Dotted Bee-fly)?
My good friend Nick Moran, who runs BirdTrack, couldn’t find one but thought that perhaps the reason was that it would be very hard to prove an apparent downgrading was solely down to the increase in observers and not because of a natural climb in population. He’s probably correct, but ecologists must be aware of the ‘effect’ – because if not, surely population data for many of our lesser known flora and fauna must be inevitably skewed?
All images copyright Charlie Moores/Talking Naturally