On the odd warmer days, hoverflies have been more easy to find and more species have been emerging. In the early May blog I mentioned the appearance of the 'Heineken Hoverfly' Rhingia campestris. Its close relative R. rostrata is also on the wing now in our ancient woodlands. The two species can be separated in the field if good close views of them are obtained. On the wing it is very difficult to separate them. The former species has narrow black edges to its abdominal segments (tergites), brown to black legs and a bronzy top to the thorax, whereas R. rostrata has a pure orange abdomen, more orange legs and a bluish grey top to the thorax. This latter species has only been found in Northants for the past few years. It was formerly confined to the South and West of Britain but has been expanding its range North and East. It is now frequent in our local woods, although I have yet to see it in my garden.
Rhingia campestris showing more bronzy thorax, darker legs, black edges to the tergites and slightly longer "snout".
The most interesting hoverfly for me so far has been Criorhina berberina, a very good bumble bee mimic, which I saw feeding on wayfaring tree flowers in one of the Yardley Chase woods. These hoverflies have larvae that feed in rotting tree roots and are associated with ancient woodlands.
Now that the hawthorn is coming out, the St Mark's fly Bibio marci is becoming frequent. This largish black fly can be seen in swarms around the flowers of hawthorn. It gets its name from coming on the wing around St Mark's Day, 25th April. However the late Spring has delayed its appearance and I did not see one until 15th May. Another frequent visitor to hawthorn is the empid fly Empis tessellata. This is a large empid with a long, straight, downward-pointing proboscis, dark in colour with yellowish bases to its wings. It is a predator of other flies but can also been seen drinking nectar at a variety of flowers. I have seen one capture a Syrphus hoverfly and kill it.
Another very common empid at present is the smaller, yellow Empis trigramma. It gets its scientific specific name from the three dark stripes on top of its thorax. However, that is not enough to identify the species as there is another very similar empid also on the wing E. punctata. The two are separated from each other by the arrangement of bristles on top of the thorax. I have recorded both locally in the last couple of weeks.