As part of the Forest of Dean & Wye Valley Batscape Project, a hedgerow survey training day will take place at Puzzlewood on 26 April. If you wish to participate, booking is essential. For full details, please click on the link below.
This note was written for the national Hoverfly Newsletter and has been published in the autumn 2017 edition issued by the Dipterists’ Forum. It may interest some other naturalists too.
On 19 August 2017 I visited a large woodland site in the Cotswolds. The weather was cool and there had been rain during the night; the grass was still wet in the lower and more shaded rides. As there was very little insect activity I decided that I would spend some time photographing the Naked Ladies which were a conspicuous and colourful feature of the scenery. By Naked Ladies, of course, I mean the flowers of Colchicum autumnale, also known as Meadow Saffron.
My eye was soon caught by an unusually downward facing flower within which there seemed to be some activity going on. I found that there was a female Ferdinandea cuprea moving around inside the base of the inverted flower. The hoverfly may have been foraging for nectar or pollen but as the surroundings were devoid of flying insects, and because of the hesitant way it began to emerge from the flower on my approach, I formed the impression that it might have been sheltering under the tent of petals for some time.
The day warmed up later, but not very much, and the few flowering plants in the woodland continued to attract almost no hoverflies. I had walked some distance from my first sighting of F. cuprea when I spotted a particularly shapely group of Naked Ladies and decided to take their photograph. While I was getting into position I became aware that a fly of some kind was coming into view and was clearly moving towards the same flowers. I quickly took my shot, hoping that the fly might add some interest to the image. Fortunately, the fly came out almost as well-focused as the flowers, and is clearly again a female F. cuprea. On this occasion the hoverfly did not land on the flower; it apparently detected my presence, changed course and flew away.
These two separate sightings of F. cuprea with C. autumnale may be a random coincidence. However, as I am not aware of any reported association between this flower and any species of hoverfly, the observation may be of some interest. In Hoverflies of Surrey (Surrey Wildlife Trust, 1998) Roger Morris does not include C. autumnale either in the extensive list of flowers visited by hoverflies (Appendix 2) or among those mentioned in his account of F. cuprea.
No, the title of this note is not an unexpectedly pious exclamation from the script of a new Batman film, but rather the consequence of an idea that has been developing in my mind as one of the county fly recorders.
Our most common bee-fly is Bombylius major (Dark-edged Bee-fly) which appears quite early in the year (the first Gloucestershire records in 2017 are from 15 March). The species has two essential site requirements: the presence of solitary bees (because its own larvae feed on the larvae of the bees) and of the spring wild flowers which the adult flies visit for nectar. These requirements may be met in a wide range of habitats, including urban parks and gardens, but are not so easily found across intensively farmed countryside.
Although it is much less common, Bombylius discolor (Dotted Bee-fly) can also be seen in Gloucestershire. The two species are difficult to distinguish unless the pattern of dark markings on their wings can be seen clearly.
Last year it occurred to me that churchyards might be good places to search for bee-flies, particularly in the Cotswolds where some village churchyards provide oases of semi-natural vegetation within many square miles of agricultural land. This year I am continuing to explore this idea during the flight season of the adult bee-flies, which are active between March and June.
Sadly, even some of our most picturesque rural villages have churchyards in which the only natural vegetation permitted is tightly mown grass. The solitary bees may still make use of some of these places, but they are unlikely to attract bee-flies in the absence of unmanicured corners where native flowers can grow.
On the other hand there are churchyards subject to less intensive management (either deliberately or thanks to benign neglect) where springtime flowers can flourish; my experience so far suggests that, with a little patient searching, the Dark-edged Bee-fly can almost always be found in such places.
There are also, of course, intermediate situations, such as a spacious, mown grass churchyard I have visited where several trees have been removed in the recent past, but the ground flora of violets and celandine that they once sheltered is hanging on; presumably the surrounding grass will eventually overwhelm these flowers, but for the moment they are still attracting bee-flies. Unsympathetic management is an obvious threat to the flora and fauna of our churchyards; perhaps the presence or absence of bee-flies could play a part in assessing their wildlife value, in both rural and urban parts of the county.
During several recent journeys through Willersey, in the north of the county, I had noticed that the ornamental pond on the village green seemed to have become largely covered by some kind of vegetative growth, much of it a reddish colour. I eventually took an opportunity to park nearby and had a closer look. It turns out that the surface of most of the pond has been colonised by the Water Fern (Azolla filiculoides), an introduced species from the Americas which was first recorded over here, at Pinner in Middlesex, in 1883. I have come across this fern from time to time but it is sensitive to our winter temperatures and I am not aware of any persistent colony in our part of the country. It is quite likely that there will be no sign of it at Willersey next year!
Water Fern is very different from any of the other ferns found in the British Isles. It does not root itself in the soil, but floats free on the surface of still waters it has colonised. The individual plants remain tiny and reproduce readily by simply breaking apart. By this means the plant can spread quickly across the surface of a suitable body of water.
Although it is not well-known in this country (as a non-native, it has been given rather limited cover in the standard field guides) Azolla is a significant member of the flora elsewhere, particularly in rice-growing areas. Pockets within the leaf lobes floating at the water surface usually house the nitrogen-fixing cyanobacterium Anaboena azollae. In China and Vietnam the native Azolla pinnata was cultivated for hundreds of years so that the nitrogen rich ferns could be used as fertiliser for the rice crop; quite recently A. filiculoides has largely taken over this role as it has proved to be a little more cold-tolerant and a great deal less susceptible to insect attack. Azolla is also used as animal feed in its native regions, and for mosquito control (principally by denying egg-laying females access to the water surface).
Like other ferns, Water Fern can reproduce by means of spores, but very little seems to be known about the extent and significance of this within the British Isles.
Elsewhere, attempts to stimulate significant spore production for commercial purposes have apparently failed, so taking advantage of the plant’s capacity for prolific vegetative reproduction remains the only viable option where cultivation is practised. It is likely that accidental and deliberate introductions by aquarists account for much of the Water Fern’s British distribution but transport of spores and plant fragments on the feet and feathers of birds is also a possibility.
There is evidence that Water Fern has become more common in recent years; this could be a reflection of our changing climate. Perhaps we should be showing more interest in this introduced fern that may have become an established resident, particularly in view of the unique features of its biology and lifestyle. It would be interesting to know whether it is, in fact, persistent at any Gloucestershire sites and whether there is any obvious pattern to its occurrence in the county.
During a morning walk through The Mythe Railway Reserve on 20 April I was surprised to find at least six of these beetles (Platyrhinus resinosus: Coleoptera, Anthribidae) resting on a log at the side of the track. The weather was sunny but cool and it appeared likely that the beetles, scattered along the top of the log, were warming themselves there.
On previous occasions when I have encountered this beetle I have only seen single individuals, and it was strange to find so many in one place. David Atty (Coleoptera of Gloucestershire: 1983) particularly associated them with the fungus Daldinia concentrica (King Alfred’s Cakes) and seems to have regarded the species is as a relatively uncommon one in our area.
As the adult beetles spend a lot of their time keeping quite still, their resemblance to bird droppings probably provides both protection from potential predators and effective concealment from wandering naturalists; perhaps they are more widespread than we realise. When I passed the same log again a little later most of the beetles had disappeared, and after an hour they had all vanished, presumably to explore the nearby vegetation.