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.

Oak apple galls

Oak apple gall caused by cynipid wasp, Biorhiza pallida

The leaves have only just started to open on this oak tree, a Sessile oak I think, yet it is already covered by many galls. These rounded disfigurations – called Oak apples – are caused by a tiny (5-6 mm) wasp in the family Cynipidae, called Biorhiza pallida. 

Freshly emerging foliage on oak free, 9th April 2017

It is known that the galls are caused by the injection of venom by the wingless, parthenogenetic females, which cause the newly emerged leaves to soften and swell up. These females have emerged from galls growing underground, on the roots, and they have crawled up the tree to start a new generation in the Spring. (1) The eggs hatch and the larvae secrete chemical substances which also cause the tissues to grow and form into a ball; the apple gall.

Oak apple gall caused by the cynipid wasp, Biorhiza pallida

Remarkably, all of the individual wasps developing within a given gall, of which there may be as many as thirty, are of the same sex. (2) Although the gall is made of plant material, because it is induced by the wasp it is said to represent the extended phenotype of gall-wasp genes (Stone and Cook, 1998). (3)

Oak apple galls higher up the tree

The tree was located near the Felmersham Gravel Pits, a Site of Special Scientific Interest between the villages of Felmersham and Sharnbrook, in Bedfordshire.

Oak tree with Oak apple galls, Bedfordshire

The life cycle of these amazing wasps is even more complex than I have outlined here, with individual asexual females able to produce both males and females from unfertilised eggs; alternating sexual and asexual generations and way of life that utilities both the below-ground roots and above-ground shoots of the tree.