The immigration of thousands of Painted Lady butterflies into the UK has been well recorded but hoverflies are also migratory and we have seen a large increase in the very common Marmalade Hoverfly, Episyrphus balteatus, in the last couple of weeks. In past years, when this has happened there have been hysterical headlines in the popular press about mass invasions of wasps, although they were in fact hoverflies and completely harmless (unless you are an aphid!).
On 2nd I visited a local spring-fed marsh. In just over half an hour I found 5 species of Soldier Fly there. Oxycera nigricornis (Delicate Soldier), Oxycera rara (Four-barred Major), Nemotelus pantherinus (Fen Snout), Oplondontha viridula (Common Green Colonel) and Chloromyia formosa (Broad Centurion) were present in good numbers. Apart from the widespread Broad Centurion these are not well recorded in the county.
I found a Tachinid Fly, Sturmia bella, in the south of the county on the 9th. This is an introduced species, believed to have entered the country via someone importing larvae of Vanessid butterflies. It is a parasitoid of these butterflies and may be linked to the recent decline in Small Tortiseshell.
On 10th/11th I took part in a survey for the Wildlife Trust of a damp meadow area in Northampton. The weather conditions were poor so not much was found but I was pleased to find another Soldierfly, Pachygaster leachii (Yellow-legged Black Soldierfly) and the Hoverfly, Eupeodes latifasciatus. This latter species is believed to be partially migratory. It is widespread but scarce and fluctuates in numbers from year to year. It is associated with rushes in damp meadows. A couple of common snail-killing flies, Sciomyzidae, were also found: Ilione albiseta and Pherbina coryleti.
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