Hoverfly Common Dronefly (Eristalis tenax)

Common Dronefly (Eristalis tenax) Size 9.75-13.0mm. Flight Mar-Nov.

Species of the week – 3^rd November.

This is a hoverfly that, as the name suggests, is common and can be spotted any month of the year. As I write this in November it is one of the few hoverflies that I can come across on a milder day, because females are known to hibernate. In Spring it is often one of the first hoverflies I see hovering in a shaft of sunlight, lekking over a dandelion flower in the hope of mating with a passing female. This hoverfly is known to dangle its legs as it hovers, so is identifiable in the air even if out of reach to see its markings. Come Autumn go to any Ivy bush in the sun and I am sure to see one of them, along with its cousin the Tapered Dronefly (Eristalis pertinax).  

The Common Dronefly is often spotted in gardens but more so ‘beyond the garden gate’. It is often seen around the flowers of Blackthorn and Hawthorn early season, as well as Bramble, Dandelion and Thistle flowers. They are vital for pollination of crops like Carrots, Onions, and Radishes, especially under cooler conditions when bees are less active. All these flowers are typically not garden plants, but the Dronefly will visit open flowers like garden daises if they can get their short tongues to the nectar.

Common Dronefly belongs to a group of hoverflies with a distinctive loop in its wings, see diagram below. Although a distinctive feature, there are other tribes namely the Merodontini to which the Narcissus Bulb Hoverfly (Merodon equestris), as well as other Eristalini i.e. Footballer (Helophilus pendulus), where this loop in the wing can be observed - so caution in identification is advised. 

Diagram 1: Typical wing of a Dronefly

The Dronefly belongs to a group with ten other hoverflies, each with similar markings on the face and abdomen, so care is required when identifying it. At first glance it looks like a male honeybee, known as a drone, from which it gets its name. The large eyes and smaller antennae of a dronefly should help distinguish it from a honeybee with smaller eyes and large antennae, see below. 

A Honeybee (Apis mellifera)

A Common Dronefly has typically a dark body with orange markings on tergite 2, the segment close to the thorax; there could be an orange marking on tergite 3 (often only seen in males) but not usually the 4^th. A bee in comparison has typically more complete orange bands on the abdomen, between the tergites, see above. Check to see if the face has a dark broad black stripe. Books often stipulate to check for vertical stripes on the eyes, but this is not an easy feature to observe in the field and could be just lighting, thus resulting in misidentification. If the front, middle, and back legs are dark and the middle segment of the back leg is enlarged and curved, an imitation of a bee’s pollen sac, then it is more likely you are looking at a Common Dronefly. If the front and middle feet are wholly orange, then it is a Tapered Dronefly, especially if its abdomen is conical shaped.

The annotated photographs below show the loop in the wing, darkened body with orange markings on the tergites of the abdomen and the enlarged curved back leg. These are the features I look for when out in the field. For more information about how to separate it from the other 10 Eristalis species then please do check out the books page for recommendations.

The adult dronefly will look for a natural rot hole or man-made hoverfly lagoons to lay its eggs. The adult will lay its eggs into a soup of detritus material, rotting vegetation of leaves or grass, preferably where the larva can live and feed once hatched. The larva is cream white with a long tail which functions as a breathing tube, a snorkel to take oxygen from the air. Here it will live, going through 3 moulting stages, before crawling out and turning into a pupa where it can metamorphose into an adult when conditions are right.