- Episyrphus balteatus, which seems to be having a good year and was far more abundant than expected in the winter.
- Eristalis pertinax, which has appeared to be poorly represented in recent data.
- Eristalis tenax, which appears to have been more dominant in recent data.
- Helophilus pendulus, which has generated regular comments about its apparent scarcity.
- Rhingia campestris, which has been notable by its absence even though it is a highly distinctive species.
Episyrphus balteatusThis is an aphidophagous species that occurs throughout the year but in particular dominates the records at certain times. In mid-summer, it vastly outnumbers all other hoverflies but peaks at differing times.
|Figure 1. Episyrphus balteatus|
Eristalis pertinaxThe larvae of Eristalis (and Helophilus) are aquatic. E. pertinax usually has two peaks, one in the spring and the other in late-summer. Numbers should start to rise in July but as yet that has not been detected.Late autumn abundance is very variable, depending upon both temperature and sunshine. It usually starts to disappear in late October but can be abundant into December during warm autumns.
|Figure 2. Eristalis pertinax|
Eristalis tenaxAdults usually hibernate, but in recent years this has been considerably less clear from the data. Winter 2018-19 was relatively warm but the numbers of E. tenax recorded seem to have been lower than the longer-term trend.
|Figure 3. Eristalis tenax|
Helophilus pendulusMonitoring the Facebook group has pointed to this species having not been as numerous in previous years. The phenology for 2019 is somewhat odd, with a much shorter spring generation.
|Figure 4. Helophilus pendulus|
|Figure 5. Helophilus pendulus phenology in England & Wales|
|Figure 6. Helophilus pendulus in Scotland|
Rhingia campestrisThis is a highly distinctive species whose larvae develop mainly in cow dung, although its distribution suggests that a wider range of dung is probably utilised. It is a species that has, historically, been considered to respond to hot summers and for some generations to almost completely fail. This was detected in 2018 and the response in 2019 is therefore of interest.
What emerges is a response that seems to be completely different in Scotland. Whilst there seems to have been a uniform crash in England and Wales, numbers in Scotland appear to be robust and possibly higher than in recent years. I suspect that the data for northern England may ultimately show a similar pattern to Scotland once records from various very active recorders are absorbed into the dataset (at the end of the year). Those from more southerly regions seem to suggest that numbers are exceptionally low; which is consistent with the failure of the summer generation in 2018 and thus a failure of breeding success to create the spring generation.
|Figure 7. Rhingia campestris in England and Wales|
|Figure 8. Rhingia campestris in Scotland|