|Animalia: Athropoda: Hexapoda: Insecta: Diptera: Syrphidae: Scaeva pyrastri|
After a fairly dismal weekend the sun has been shining for the past 2 days, with surprising results. The garden has been full of hoverflies, with 6 different species and also in higher numbers than I seen before. One of which is new to me and to the garden, the Pied Hoverfly, Scaeva pyrastri. This is a relatively large hoverfly, between 10-5-12mm in length1. The patterning is pretty distinctive with white, comma-shaped spots (yellow in S. Selenitica) on a black background. This, in conjunction with the inflated front, makes it quite unmistakable, swell that is for those who know what they’re looking at, I had to scour the fieldguide. Completely black individuals can occur, but are usually recognisable by the inflated front.
A migratory species which, like Red Admiral or Clouded Yellow butterflies, arrives in the UK in highly variable numbers. Something that Brexit will struggle with! In some years it is almost absent, but when it does occur it may breed locally. Although this species can turn up almost anywhere it is scarcer in the at altitude and the north in the UK. Being migratory first sightings can be variable, and I assume must depend upon the prevailing weather conditions. The season starts around May and continues through to November, peaking in August 1,2. As the larvae feed on aphids the spread north across Europe depends upon aphid blooms, and as their prey populations rise then the migration wave follows this northwards. In Ireland and western Scotland, the earliest records are in July, suggesting that it is does not usually manage to breed in these areas.
So where can I find? Well, my garden is certainly one place this year. But it can also be found almost anywhere, especially where there are aphids. Adults inhabitat clearings, tracksides, hedgerows, gardens 1,2. I can vouch for the fact that they are fast flying – having chased them around the garden trying to photograph them. The following is a list of flowers visited by adults: Umbelliferae; Calluna, Campanula rapunculoides, Cirsium, Convolvulus, Eschscholzia californica, Euphorbia, Hamamelis, Leontodon, Ligustrum, Lycium chinense, Parnassia, Pulicaria disenterica, Rubus fruticosus, R. idaeus, Senecio, Solidago virgaurea, Tripleurospermum inodorum, Ulmus 3,4.
S pyrastri is a member of the Syrphidae family of hoverflies, and they lay their eggs on leaves and stems of plants infested with aphids. In my case they seemed to be interested in the aphids on the Boarge, and so were the Marmalade Hoverflies – Episyrphus balteatus. The eggs hatch in 3 to 4 days into soft-bodied maggot-like larvae, and feed for 7 to 10 days, then drop to the soil to pupate. A life cycle from egg to adult is completed in 16 to 28 days5. Though I would assume this is dependent up in temperature. There can be between three to seven overlapping generations each year, but this is dependent upon the available food and weather conditions. But C. pyrastri doesn’t have it all it’s own way. The larva of Enizemum ornatum is parasitoid of the larva.
The UK distribution is widespread in the lowlands of the southern half of Britain. In northern England and southern Scotland records are noticeably clustered along the east coast, a reflection of it being a migratory species.
- Ball, S. & Morris, R. Britain’s Hoverflies: An Introduction to the Hoverflies of Britain. Wild Guides. (Princeton University Press, 2013).
- Pied Hoverfly – Scaeva pyrastri. Nature Spot Available at:
http://www.naturespot.org.uk/species/pied-hoverfly. (Accessed: 27th July 2017)
- Helyer, N., Cattlin, N. D. & Brown, K. C. Biological Control in Plant Protection: A Colour Handbook, Second Edition. (CRC Press, 2014).
- Bugg, R. L., Colfer, R. G., Chaney, W. E., Smith, H. a. & Cannon, J. Flower Flies ( Syrphidae ) and Other Biological Control Agents for Aphids in Vegetable Crops. Div. Agric. Nat. Resour. 8285, 1–25 (2008).
- Ralph, E. B. Insects and Mites of Economic Importance in the Northwest. (1998).