What makes them different?
The head of a hoverfly is not only vital, but a fascinating structure designed for several functions some will be obvious and other less so. The intention of this blog is to do an overview of the components of the head that directly or indirectly contribute to flight, feeding, and sensory perception. A separate more in-depth article is probably required to delve into each component, watch out for those posts at some later date.
Let’s compare a hoverfly head with a bee’s head, which although it may look similar has several interesting differences, see below. I hope to explore those differences, whilst giving ecological and evolutionary reasons for such adaptations and pointing out taxonomical purposes along the way.
Outwardly there are six external features worthy of examination and discussion. Most of these features are connected to the brain and nervous system which not only processes the visual and olfactory information, but motor control for precision flight to assist in finding flowers and mates, and yet provides split-second decision-making needed to hover and evade predators.
So, let’s ‘head-in’ and see what we can find…. Sorry I couldn’t resist the pun.
Compound Eyes
Both compound eyes contain thousands of ommatidia (tiny lenses), enabling them both to detect movement and colour patterns, including UV light for flower recognition. The eyes are much larger on a hoverfly than a bee, the eyes in the fly giving almost 360 vision which is useful for predator avoidance. A bee on the other hand has a built-in defence mechanism, the stinger, so their eyes although more typical of a hunter, are just a relic from their evolutionary past, having evolved from Hymenoptera wasps.For most species of hoverflies, the males have larger eyes that meet in the middle (holoptic) whereas for females there is a gap (dioptic) this can be used for sexing. Colour and hairiness can be important in identification, eyes of the Eristalinus genera are even spotted, but most are orange-red-brown with little variation between species.
Here’s a question is it easier to catch a hoverfly or a bee?
Comment below if you know the answer.
Ocelli
These are simple eyes found in all insects, three simple eyes (lens) in the shape of a triangle used for light sensing. Both the bee and the hoverfly use what is called a time-compensated sun compass, which allows them to adjust their heading as the sun moves throughout the day. They are also thought to be used to measure day length and regulate their internal clock. In bees, its role is to assist in flight paths to and from nests whereas in hoverflies they are used for detecting predators, flight stability and for some species, migration.
It also helps to evade me capturing them, needed for further examination and identification before release. Sorry hovvies!!!
Click on this link to find out more about a hoverfly’s migration
Antennae
This is the most obvious difference between the two and at a glance the second most important visual identification to make in hoverfly spotting (the first being the colouration of the abdomen). Bees have evolved longer antennae, 13 segments used for colony communication and scent-based navigation. A hoverfly relies on visual cues rather than scent-based navigation, they are not colonial and therefore don’t require as many chemoreceptors for detecting pheromones and scents. So, they have much shorter antennae only 3 segments the 3rd being the largest and furthest from the face which bears the arista. The position and shape of the arista can be useful in species identification. Volucella species have plumose (feathery) arista much like a male moth, in most other species they are bare. Others have slightly different shaped antennae like those of Callicera, Chrysogastrini and Rhingia genera, see below. In the Cheilosia genera, little black jobs as I call them, antennae shape and colouration can be a key feature in species identification.
Mouthparts
Hoverflies have a retractable, tubular sucking organ with a sponge like proboscis, used for sucking up nectar, honeydew and collecting and crushing pollen, they have no mandibles like bees. Bees have mandibles to perform nest or colony activities, collecting pollen to line their cells in solitary bees or moulding wax flakes into a honeycomb as in the case of the honeybee. I often notice in my Foxglove (Digitalis purpurea) and Comfrey (Symphytum officinale) tiny little holes at the base of the flower. These holes are made by bees with short tongues like Buff tailed bees (Bombus terrestris) who have learnt to use their mandibles to pierce a hole, gaining access to the nectar source which would otherwise be unavailable. Clever….Most hoverflies have typically short tongues, and no mandibles with which to bite holes in the tubular flowers, so prefer more open flowers. But there are exceptions with some hoverflies having evolved longer snouts, i.e. the Rhingia species see above, this appendage adaptation allows it to have a longer tongue. They are sometimes referred to as ‘Heineken flies,’ in reference to a beer commercial on UK TV (1973-95), which had the slogan ‘refreshes the parts other beers cannot reach.’ So, the Heineken fly (Rhingia campestris and rostrata) can reach nectar sources other hoverflies cannot reach!
Labella – sponge-like pad covered in fine grooves called pseudotrachae. These grooves soak up nectar by capillary action.
Hypopharynx – slender needle-like structure running the centre of the proboscis.
Glossa – tongue in a bee used for mopping-up nectar.
Facial features & Sensory hairs
Many bees have hairy faces which assist in collecting pollen but also aid in warmth and insulation. Whereas for hoverflies most faces are bare or have a dusting of tiny, flattened hairs, which are less effective for carrying pollen but maybe important in detecting air movement. For some hoverflies, the face often has a bulge or knob resembling a nose, these along with the frons (brows) and cheeks can vary enormously between species and often is used in taxonomical identification. A lot of hoverflies have yellow faces, again an adaptive mimicry of wasps and bees.Brain
Although hoverflies and bees share similar head features, these traits evolved to support vastly different lifestyles and behaviours. It follows that their brains—and the neural wiring within them—must also differ to enable these adaptations. Bees have evolved neural networks suited to storing food, allowing them to use their senses to forage and return resources to the nest, or to support the colony. Hoverflies, by contrast, have developed neural systems adapted for a solitary existence, prioritising survival through precise flight control. While the two brains may appear outwardly similar, the underlying neural networks that drive these distinct functions are fundamentally different.To summarise:
• Hoverfly head = visual precision + mimicry + hovering flight. Adapted for solitary life, mimicry, and aerial precision.• Bee head = olfactory communication + pollen handling + colony/nesting tasks. Adapted for social organisation, resource collection, and nest/hive maintenance.
Sources:
Rotheray G.E & Gilbert F.S 2011 The Natural History of Hoverflies. Forest TextStuart, B & Morris R 2024: Hoverflies of Britain and Ireland, Wildguides
Further Reading
If you enjoyed this article please consider reading 'Are Hoverflies Masters of the Air?' about hoverfly wings.
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