Black-rimmed snout hoverfly: the Heineken Fly!

Rhingia campestris Meigen, 1822 showing snout close-up
Rhingia campestris Meigen, 1822 inserting proboscis into Primula flower

The Black-rimmed snout hoverfly, Rhingia campestris Meigen, 1822 (Diptera: Syrphidae) is a common and widespread fly which is often seen visiting flowers or resting on nearby vegetation. The larvae live and develop in cow dung, whilst the adults feed on nectar and pollen. Pollen is required by the females as a protein source for egg development; nectar is needed by both sexes, and as such they are important pollinators of flowers, specialising in species such as bugle (Ajuga reptans), red campion (Silene dioica) and spiked rampion (Phyteuma spicatum). (1, 2).

Rhingia campestris Meigen, 1822 with proboscis inserted into corolla of Primula flower

This distinctive fly has a long, stubby, duck-billed shaped, snout and an extendable proboscis, as long as its body (7–11 mm). It also appears to have been given the name ‘Heineken fly’, after an advert on UK television, because it can supposedly reach the parts of a flower that other hoverflies cannot! I prefer the traditional name: Black-rimmed snout hoverfly. The black rims refer to the black margins of the tergites: the sclerotised plates on the dorsal (upper) sides of each abdominal segment. The similar, conspecific species, R. rostrata, lacks the black margins.

Rhingia campestris cleaning proboscis. Note black-margined tergites on abdomen.

An organ, if that’s what it is, of this complexity and functional importance to the fly must be cleaned and looked after. The proboscis, when not in use, is folded up and stored within the snout, as can be seen in the very high magnification photograph in link number (3). I wonder if anybody has studied the proboscis in detail and worked out exactly how it is extended and folded up? The following photograph is not very good, but is the best one I have of the extended proboscis in side view. The proboscis is clearly a complex structure and one that must have evolved to allow the fly to access deep nectar sources.

Rhingia campestris Meigen, 1822 with proboscis extended
  1. Haslett, J.R. Oecologia (1989) 81: 361. doi:10.1007/BF00377084
  2. Kooi, C. J., Pen, I., Staal, M., Stavenga, D. G., & Elzenga, J. T. M. (2016). Competition for pollinators and intra‐communal spectral dissimilarity of flowers. Plant Biology, 18(1), 56-62.

Bee-flies: the dipteran narwhals

White-tailed bee-fly (Bombyliidae) showing wing venation
White-tailed bee-fly (Bombyliidae), possibly Bombylius posticus, showing wing venation

I always enjoy seeing bombyliids (bee-flies). They sound like little helicopters, hovering and buzzing about, and their furry appearance gives them a certain cuteness. They are flies pretending to be bees!

Not the easiest of insects to identify from photographs though. This one looks rather like Bombylius posticus, which has a wide Palaearctic distribution, but I am not sure if it is found in northern Thailand, where I took the photograph. This species has prominent white tufted scales at both the base and apex of the abdomen. (1). Alternatively, it might be a variant of Bombylius major, which is found in Thailand.

White-tailed bee-fly (Bombyliidae), possibly Bombylius posticus, showing white scales
White-tailed bee-fly (Bombyliidae), possibly Bombylius posticus, showing white scales

Why would they want to mimic bees? One reason might be that they avoid predation by other insects which think that they are bees, i.e. armed with a harmful sting. Although they don’t have a stinging apparatus like a bee, they do have a very prominent, needle-like proboscis sticking out in front of their heads. They use this stiff, unretractable organ to penetrate and probe flowers for nectar. It almost looks like they are carrying a little spear or javelin; the dipteran equivalent of a narwhal! According to Wikipedia, some people in East Anglia call them beewhals. (2)

Bee=fly (Bombyliidae) in flight, showing proboscis sticking out in front
Bee-fly (Bombyliidae) in flight, showing proboscis sticking out in front

Another reason why they might benefit from resembling bees, is that they lay their eggs in the nests of bees and wasps. Indeed, they actually flick their eggs into the nests of some solitary bees, whilst hovering above the nest opening. (See links 3 and 4 for videos of this behaviour). Flicking, or shooting eggs from a safe distance, as one blogger aptly put it! (5) The tufts at the end of the abdomen are reportedly used to collect dust prior to flicking the eggs, something that would be fascinating to watch!

The bee-fly larvae are ectoparasitic, meaning that they attach onto the outside of the bee larvae in order to feed on their body fluids. Perhaps their bee-like appearance helps the adult bee flies get close to bees nests without being attacked? Different species are also parasites, and hyper-parasites, on a wide range of insects, including butterflies, grasshoppers, wasps, other flies, beetles and cockroaches!

White-tailed bee-fly (Bombyliidae) resting.
White-tailed bee-fly (Bombyliidae) resting.

The adults feed on pollen and nectar and are important pollinators, indeed some plants species depend upon them for their survival. There is a nice little blog about bee-flies in a Scottish garden (6).