Orchid bees – flying jewels that pollinate flowers

Male of Euglossa heterosticta approaching flowers (right) and landed on them (left), La Selva Field Station, Costa Rica, June 2018; © M. O’Donnel.

Honeybee males are called drones (see also here). They do not have sting, do not make honey, do not even feed themselves but are rather fed by worker bees; their primary role is to mate with virgin queens. As result, drones have acquired a rather negative reputation among humans. From the ancient times till now, drones have been regularly described as ‘lazy loudmouths’, ‘greedy lozells’ or even ‘virulent weeds, to be eradicated’ (Fig. 1). They “lazily consume the labours of the bee” – said Hesiod in his Works and Days (c. 700BS); so drones were not even seen as the bees. Thomas Moffet (1658) in his Insectorum wrote about drones:

“Both God and man disdain that man

Which Drone like in the blue,

Nor good nor ill, endeavour can

Upon himself to live,

But idle is, and without sting,

And grieves the labouring Bee,

Devouring that which he home brings,

Not yielding help or fee.”

Fig. 1. Greedy drones, as depicted in Cotton’s Buzz-a-Buzz. © The Bodleian Libraries, The University of Oxford. In the frame at the left top corner, a honeybee drone from the collection of the Manchester Museum.

Sometimes drones are depicted as indolent, small-brained creatures that are anatomically unfitted for foraging, in other words, for doing THE important job – i.e., collecting nectar and making honey for us, humans. Indeed, what impudence!

Perhaps drones are not altogether idle and do help in warming and cleaning the hive, and secreting a special jelly used for feeding brood. Yet the truth is that after the breeding season all drones are evicted from the hive or slaughtered by female workers if they resist eviction. Their life is short and basically serves one purpose only – mating, but who would dare to say that this JOB is not important?

However, drones in some other groups of bees, for instance, orchid bees (see also here) demonstrate a far more complex lifestyle and are notable for their important role in pollination, especially of orchids – this is why their name. As the famous Spanish poet Antonio Machada (1875–1939) put it, “Bees, singers not for the honey but for the flowers”. Orchid bees are also distinguished by their shiny metallic coloration and resemble living jewels (Fig. 2).

Fig. 2. The male orchid bee Exaerete smaragdina from Costa Rica in the insect collection of the Manchester Museum. © The Manchester Museum.

Orchids are the most species rich plant family, accounting for more than 10% of all flowering plant species. Male orchid bees pollinate over 25% of the orchid species (c. 2,000) from tropical Americas. More than 600 orchid species depend solely on male orchid bees for pollination. Males do not specialize in one or a few orchids and visit many different species. Although females of some orchid bees pollinate nectar-producing orchids such as Sobralia (in that mode resembling other bee pollinators), it’s the males that are much more important in orchid pollination. This unique mode of pollination is sometimes called the ‘perfume flower syndrome‘ – that is a selective attraction of male orchid bees to orchid flowers.

Male orchid bees are strong flyers. While visiting numerous flowers, individual males are able to travel long distances from 400-800 m to 5-6 km in a single trip, or even to cross the distance of 45-50 km within a few days. The longest flight distance ever recorded for a male orchid bee (Euglossa viridissima) from Yucatán, Mexico was 95 km, crossed in 12 days. Isn’t that an impressive achievement for a housefly-sized creature?

But why do male orchid bees visit orchids and other flowers? Certain flowers are visited to feed on nectar and pollen, as all bees do. However, males do not collect nectar for producing honey. Making honey is still the duty of orchid bee females. Yet the majority of flowers visited by drones usually lack nectar but are very fragrant, with bees being attracted by flower scent. Indeed, they visit flowers to collect aromatic compounds to render themselves attractive to females, and also for chemical signalling to their rivals during territorial display. Males also collect fragrances from non-floral sources, such as plant wounds, fungi or even rotten wood.

Fig. 3. Male of Eulaema cingulata from the collection of the Manchester Museum: A – brusher of the front tarsi; B – tibial organ of the hind legs, modified from Dressler (1968: fig. 1).

While visiting a flower, a male brushes on the surface of the flower with hair pads of its forelegs (Fig. 3), collecting the fragrance oils. Usually the bee brushes for a short time, then hovers near the flower and transfers the collected substance via midlegs to a specialized hollow pocket in its enlarged hind legs in which the scents are stored. The male repeats this behaviour many times, sometimes remaining on one flower or inflorescence as long as 90 minutes. This behaviour is shown on the following short video.

Drone receives a pollen sac (=pollinarium) as it leaves the flower or during collecting fragrance oils, as shown in Fig. 4. Pollinaria are usually glued to a dorsal side of bees: head, thorax or abdomen (Fig. 5), also to antennae and legs. Individual bees often can carry the pollinaria of more than one orchid species. Having received pollinaria, drone flies away and then visits another flower of the same orchid species where the pollinaria are detached and pollination takes place.

Fig. 4. Pollination of the orchid Stanhopea grandiflora by male orchid bee Eulaema meriana: (A) The bees enters in the saccate base of the flower lip; (B) The lip is very smooth and slippery, the bee may fall while withdrawing, attaching pollinaria (in yellow) to its thorax; (C) Dorsal view of the bee with the pollinaria attached; (D) Outline of the bee showing placement of the pollinaria from side. Modified from Dressler (1968: fig. 2).

Many orchids are very scarce in nature, with individual plants being separated from each other by long distances. Therefore, male orchid bees are to be really strong flyers to visit several flowers of such orchids in a single trip. Indeed, these bees are strong flyers (see above).

Fig. 5. Outline of an orchid bee male showing how pollinaria of different orchid groups can be attached: (A) Notylia; (B) Lacaena; (C) Mormodes, goblin orchids; (D) Cycnoches; modified from Dressler (1968: fig. 4). On the right: male of Euglossa imperialis from Costa Rica carrying two pollinaria, © J.H. Marden.

According to one hypothesis, the main reason why male orchid bees collect floral fragrances is that it helps them to be more competitive when mating. A female seems to choose a potential mate based on its ‘quality’ which is associated with the complexity of a perfume presented by the male. Females prefer males with more complex bouquets, which can contain up to a dozen of aromatic compounds. A complex perfume is correlated with greater male fitness: i.e., its strength and physical characteristics. The male that is able to fly long distances and to visit more flowers can present a more complex bouquet; it also means that such male lived longer and hence its survival rate is higher. As male physical characteristics are heritable, the offspring from a stronger male will have higher chances to survive.

The orchid bees’ attraction to floral scents is used to study their diversity, daily activity, flight ranges, etc. by means of chemical baits. Please, watch the following video on how to attract and count orchid bees.

Further reading

Birchall E. 2014. In praise of bees. A cabinet of curiosities. Quiller, Shrewsbury, UK, 256 pp.

Cameron S.A. 2004. Phylogeny and biology of Neotropical orchid bees (Euglossini). Ann. Rev. Entomology, 49: 377-404.

Dressler R.L. 1968. Pollination by Euglossine bees. Evolution, 22(1): 202-210.

McHatton R. 2011. Orchid pollination: exploring a fascinating world. Orchids, June: 340-349; online

Roubik D.W. & Hanson P.E. 2004. Orchid bees of tropical America. Biology and field guide. Sna Jose: INBio, 370 pp.