John Attiwell, Seasonal Survey Officer for the Cairngorms region, takes us down to a hidden part of the Highland Wildlife Park, to meet a very special creature and learn more about the work being done to save it.
In the shed, something moves in a jar of ‘woodchip soup.’ It resembles a curious mix of maggot, white goo and string, a centimetre or so long. Its movements are undulating and slow, as it moves through the wood shavings, grazing on the saproxylic bacteria which feed on rotting wood in their millions. A breathing tube protrudes from its back end, stretching improbably to the water surface, a snorkel, connecting this air-breathing Pine Hoverfly larva to the world of air above. Affectionately referred to as ‘goo babies,’ some might find them unappealing, but the several thousand Pine Hoverfly larvae here represent the future of their species in Scotland.
Pine Hoverfly larvae in a jar of 'woodchip soup'. John Attiwell, RZSS Highland Wildlife Park.
Though listed as Least Concern by the IUCN, the UK status of the Pine Hoverfly (Blera fallax) could barely be more critical; the species is edging ever closer to local extinction. It’s thought to hang on at only one Cairngorms site, kept a closely guarded secret by those leading the desperate drive for its conservation. And its global status is not secure; though colonies exist across cold temperate Europe, many are reported to be declining. In the case of Blera fallax, ‘Least Concern’ does not mean without concern.
Today a special bunch of Royal Zoological Society of Scotland (RZSS) keepers and scientists are looking after Pine Hoverflies in captivity, at the Highland Wildlife Park, which hosts an invertebrate breeding facility alongside its Polar Bears and Snow Leopards. Jar upon jar of ‘woodchip soup,’ a mixture of pine shavings and rainwater, capped with moss line the shelves of a climate-controlled cabin. Biosecurity is tight and the hoverfly larvae are not on public view, for a variety of reasons, including risk from insecticides and insect repellents, potential pathogens, and the demands of maintaining the conditions for the larvae to thrive. Most of the public, gazing at the Tigers and Arctic Foxes, would not know they were there, but captive breeding represents some of the Society’s most important work.
Pine Hoverfly larvae. Genevieve Tompkins
Pine Hoverfly require conditions which mirror those they would find in the wild, and remarkably, can survive the water in which they live being frozen solid, and thawing, on multiple occasions through the winter. When RZSS first took this species into captivity, nobody was clear if captive breeding was even possible. Now they have written the book. Soon, their precious larvae will be removed from the relative safety of their state of the art, climate controlled facility which is definitely not a shed, and taken out into the wild, where they will complete their life cycle. The adult Pine Hoverfly is a splendid black fly, with a hint of Bilberry/Red Tailed Bumblebee mimicry. They have a small patch of orange-red at the tip of the abdomen, more extensive in the male, and a black thorax and abdomen. They seldom hover, indeed, and perhaps adaptively for a species tied to these cooler pine woods, tend to spend long periods basking or standing. I have not seen an adult, wild or otherwise, and the adults are said to be hard to detect, but they are one more species dependent on natural, well managed forest. The restoration of ancient Caledonian forest in Scotland has long been a conservation priority, and a key part of that mission is returning land once used for pine plantations to a more natural, wilder forest state. The RSPB and other landowners are hard at work opening gaps in the canopy, removing some of the pines by winching, ring barking and felling, to create standing deadwood, and the conditions for natural regeneration, and allowing deciduous trees such as Rowan, Aspen and Birch to return to these habitats, supporting a greater range of biodiversity. This felling represents an opportunity for the conservators of the Pine Hoverfly. Artificial rot holes are created, by a guy with a chainsaw, in the felled logs or the high stumps, into which the jars of soup and larvae can be emptied, and the larvae return to the wild with a helping hand. The rot holes support a range of species, including other hoverflies and detritivore millipedes. Further, the deciduous species will support the recovery, Pine Hoverfly emergence is timed with the appearance of Rowan flowers which are a vital nectaring resource for the adults. Gaps in the canopy and greater sunlight penetration to the forest floor provide basking opportunities, allowing the adults to warm themselves in the sunshine, providing the energy they need to continue their breeding cycle, and hopefully go on to secure the next generation, ensuring the species recovery alongside that of their ancient and precious habitat.
Pine Hoverfly adult. John Attiwell, RZSS Highland Wildlife Park.
Main image: An adult Pine Hoverfly on white flowers. John Attiwell, RZSS Highland Wildlife Park.