If your life depends on clinging on to a bee, you better have a very good means of staying attached! Attachment is a key element in the relationship between a parasite and its host, including ticks, mites and unusual flies like bee lice, discussed here.

Like most organisms, honeybees, Apis mellifera L., can be afflicted by a variety of parasites and diseases. Perhaps the most familiar one, to beekeepers certainly, is the Varroa mite (below), which transmits at least five debilitating bee viruses, including the deformed wing virus (DWV).

Varroa mites originally only occurred in Asia on the Asian honey bee, Apis cerana (below), but jumped over onto A. mellifera in the 1950s, and spread globally, together with the viruses. Varroa mites have large disc-like arolia -soft pads – which also bear claw-like sclerites used to grasp onto the bee hosts.

Another type of arthropod found on bees, an insect in this case but superficially similar to Varroa mites in appearance (see below), are bee lice (Braulidae): for example, the ectoparasite Braula coeca (below and here and here). There are two genera in this family, Braula and Megabraula, containing eight species.

The tiny adult Braulidae (1.2 to 1.5 mm long) are highly specialised flies (Diptera), blind, with no wings or halteres, reduced antennae, and legs with claws modified into combs specially adapted for clinging to the body of bees (see here for some heavily infested bees from Mauritius).

The adult bee lice are small, reddish brown in colour, and several of them – many in some cases – can live on a queen bee; but usually only one occurs on a worker bee. Remarkably, 187 bee lice were found on one honeybee queen; a record. Unlike Varroa mites, bee lice are not generally considered to cause much harm to the bees, although this view is debatable, as the larval mines disfigure the honey combs and there is some evidence that they might also be transmitting viruses.

Queen bees are a good host to choose to live on because they live longer than the other castes, they do not leave the hive (except to mate), and they receive a lot of food from attendant workers. Drones and queens are reportedly more likely to be infested by bee lice in the beehive, after mating.

Honeybees and other social insects are meticulous about cleaning their homes and protecting the hives from aliens and invaders. So, parasites and inquilines – animals that live commensally in the nest – have to somehow fool the bees into accepting their presence. The way they usually do this is to smell the same as their host: chemical mimicry, also called chemical camouflage.

The larva of bee lice live in tubular burrows, which they make by mining the inner side of the capping of the honey cells in the comb of the bee hive. This produces an appearance of being intersected with fine fractures, similar to the mines of a leaf miner.

Braula adults often occur on the heads of honey bees, especially the queens, where they feed on food from the mouth of the bee, often as it is being fed by another bee (trophallaxis). Organisms that steal food in this way from other species are usually called kleptoparasites.

It is thought that the adult Braula can induce regurgitation from its host by stroking the upper edge of the bee’s labrum until the bee extends its proboscis. There is a 1926 description of a bee louse ‘frantically clawing’ at the clypeus of a honeybee!

The ability to cling on tightly to the body of the host is one of the key adaptations of bee lice. Without a strong and secure attachment to the bee’s surface, bee lice would be unable to get carried over into new bee colonies, and they do, in fact, die if they fall off!

The exceptional attachment ability of the ectoparasitic bee louse Braula coeca (Diptera, Braulidae) was investigated by scientists from Kiel University, in Germany, see here. They found that the specialized appendages found on the feet (the pretarsus) in bee lice are divided into a large number of comb-like teeth (below), which perfectly match the diameter of the bee host’s body hairs. The strongly broadened claws, of bee lice are superbly adapted for clamping onto the bee: the claw teeth effectively interlock with the bee hairs.

Bee lice, like B. coeca, not only cling on to bee hairs, but also attach themselves to smooth surfaces like the waxy surfaces of honey combs found in the beehive. Amazingly, Büscher et al. (2022) showed that bee lice do so by walking on their claws, i.e. with the claws completely folded inwards. This brings the soft, cushion-like pads, or pulvilli, on the feet into contact with the smooth surface. The researchers produced a number of interesting videos showing the locomotion and attachment behaviour of B. coeca, bee lice, see here.

N.B. There are four other species of Braula (B. kohli, B. orientalis, B. pretoriensis & B. schmitzi) found on different bee species around the world.

References

Büscher, T. H., Petersen, D. S., Bijma, N. N., Bäumler, F., Pirk, C. W., Büsse, S., … & Gorb, S. N. (2022). The exceptional attachment ability of the ectoparasitic bee louse Braula coeca (Diptera, Braulidae) on the honeybee. Physiological Entomology, 47(2), 83-95.

Ellis, J. D., & Nalen, C. Z. (2010). Bee Louse, Bee Fly, Braulid, Braula coeca Nitzsch (Insecta: Diptera: Braulidae). Department of Entomology and Nematology, UF/IFAS Extension. Original Publication, 1-3.

Martin SJ, Bayfeld J (2014) Is the bee louse Braula coeca (Diptera) using chemical camoufage to survive within honeybee colonies? Chemoecolgy 24:165–169.

Weems Jr, H. V., & Sanford, M. T. (2004). Beelouse, Braula coeca Nitzsch (Insecta: Diptera: Braulidae): EENY-171/IN328, 11/2000. EDIS, 2004(2).

Yusuf, A., Pirk, C., & Crewe, R. (2024). A Hitchhiker’s Ride: The Honey Bee Louse Braula Coeca (Diptera: Braulidae) Selects its Host by Eavesdropping. Journal of Chemical Ecology, 1-8.