The Fascinating Orchid Bees: Euglossa and Catasetum, the Dance of Fragrances and Pollinaria

The Fascinating Orchid Bees: Euglossa and Catasetum, the Dance of Fragrances and Pollinaria

By: Francisco López-Machado

Biologist, Entomologist, and Nature Photographer

We often hear experts and the general public alike stating that bees are the most important pollinators in most ecosystems and, by extension, essential for human food production. It is estimated that approximately one-quarter of our fruit and vegetable-based diet depends directly on the action of these pollinators.

However, bees form a highly diverse group that goes far beyond the well-known honeybee (Figure 1). Although this species is now found throughout the Americas, it's important to remember it was introduced by European settlers, who already exploited it for honey and wax. Beyond the honeybee, there is a wide variety of native bees in the Americas playing crucial roles in ecosystems (Figures 2 to 6).

Figure 1. European honey bee Apis mellifera, (Family Apidae), the most common and recognizable bee throughout the Americas. Photo taken in Delaware, United States.

Figure 2. Common eastern bumblebee, Bombus impatiens (Family Apidae), the most widespread bumblebee species in North America and one of the most important pollinators within its distribution range. Photo taken in Delaware, United States.

In the case of Colombia, the country has been recognized for having one of the richest bee heritages in Latin America. According to studies, there are at least 600 documented bee species distributed across five families: Apidae, Halictidae (Figure 3), Megachilidae, Colletidae (Figure 4), and Andrenidae, among others. However, this number is believed to be underestimated, as recent analyses suggest the actual figure might be closer to 1,445–1,500 species. In fact, several experts estimate that less than half of the country's bee diversity has been identified so far.

Figure 3. Bee Pseudoauguchlora graminea (Family Halictidae) pollinating a tomatillo flower. Photograph taken in Cali, Colombia.

Figure 4. Bee Colletes sp. (Family Colletidae) feeding on a Melampodium sp. flower (Family Asteraceae). Photograph taken in Cali, Colombia.

Figure 5. Carpenter bee Xylocopa sp. (Family Apidae, Subfamily Xylocopinae) feeding on Stachytarpheta jamaicensis (Verbena family) flowers. Photograph taken in Cali, Colombia.

Figure 6. Bee Augochlora pura (Family Halictidae), widely distributed throughout eastern North America. Photograph taken in Delaware, United States.

With these figures, Colombia ranks among the top countries in Latin America for bee diversity, alongside Mexico and Brazil. The inventory is still growing, and it is estimated that approximately 60% of Colombia's bee species have yet to be formally described, highlighting the critical need for further taxonomic and ecological research.

THE EUGLOSSINI BEES

Within the vast diversity of bees are the Euglossini bees, commonly known as "orchid bees." Colombia stands out for its remarkable richness in Euglossini species, with 134 species described (as of 2016). The genus Euglossa, with 74 species, is the most diverse. Some experts point out that Colombia has the greatest variety, followed by Brazil, Peru, and Venezuela.

These bees belong to the tribe Euglossini, within the family Apidae, the same family that includes the European honeybee. To give a bit more context, it's helpful to know that within the Apidae family, there are five main subfamilies: Anthophoridae, Nomadinae, Xylocopinae, Eucerinae, and Apinae. The subfamily Apinae itself is further divided into 34 tribes, Euglossini being one of them.

There's yet another level of classification known as the "corbiculate bees," comprising the tribes Bombini, Meliponini, Apini, and Euglossini. The term "corbiculate" refers to a specialized adaptation on the hind tibiae, allowing these bees to efficiently transport materials used in nest construction.

Beyond all this classification, what makes Euglossini bees particularly famous is their close relationship with many tropical orchids—so close, in fact, that it's estimated they pollinate around 3% of all orchids, or roughly 700 species. This includes highly specialized orchid genera such as Catasetum, Stanhopea, and Gongora, among others.

Besides the adaptations mentioned earlier, Euglossini bees have developed specialized structures reflecting their unique interaction with orchids. For instance, males possess a special "brush" on their front legs to collect fragrances exuded by flowers. Even during flight, they transfer these fragrances from the front legs to the middle legs, and finally to the hind legs, where the scents are stored in a spongy structure (Figure 8). These fragrances are essential for male bees to attract females during courtship and for territorial marking.

Despite this unique association, Euglossini bees, like most bees, also feed on nectar from a variety of plants, including anthuriums (Anthurium, Araceae family) and verbenas (Verbenaceae family) (Figure 7).

Figure 7. Euglossa sp. bee visiting flowers of Stachytarpheta jamaicensis (Verbena family). Photograph taken at Parque Corazón de Pance, Cali, Colombia.

Figure 8. Male Euglossa sp. in mid-flight, displaying its metallic green coloration and thickened hind tibiae. Photograph taken in Cali, Colombia.

Some studies suggest that these bees can travel distances of more than 20 kilometers in a single day. Additionally, male bees exhibit modified hind tibiae, visibly widened (Figure 7), an adaptation that allows them to effectively collect and store fragrances.

ORCHIDS OF THE GENUS Catasetum

Talking about orchids in Colombia means entering a universe of ingenious adaptations and fascinating stories of coevolution. With thousands of shapes, colors, and reproductive strategies, it's no wonder this country is recognized as one of the richest in orchids worldwide. Among the many marvels found in Colombia’s lush flora, the genus Catasetum stands out, revealing the astonishing relationship that plants can establish with their pollinators. One of their most remarkable traits is the presence of unisexual flowers—male and female flowers are separate, with notable differences in form and function (Figures 9 to 12).

Figure 9. Male flower of Catasetum tabulare. Photograph taken in a photographic studio from a specimen collected in Valle del Patía, Cauca, Colombia. 

Figure 10. Male flower of Catasetum bicolor. Photograph taken in a photographic studio from a specimen collected in the northern coast of Colombia.

Figure 11. Male flower of Catasetum ochraceum. Photograph taken in a photographic studio from a specimen collected in Valle del Patía, Cauca, Colombia.

Figure 12. Female flower of Catasetum ochraceum, showing what appears to be a pollinium deposited by a Euglossa bee. Photograph taken in Montañuelas, Cali, Colombia.

According to current records, nearly 4,270 orchid species have been documented in Colombia, of which 1,572 are endemic (found exclusively in the country). Within this impressive total, about 40 species belong to the genus Catasetum (2023). While most of these orchids are concentrated in the Amazon and the Andes regions, the Caribbean area remains less explored. One of the standout territories is the department of Santander, where up to 14 species of Catasetum have been reported in a single location, including new records for Colombia, such as Catasetum tenebrosum. This remarkable discovery highlights the urgent need to prioritize both in situ and ex situ conservation efforts for populations of this genus in the region.

Science moves quickly, and every year new species are described. For example, in 2023, Catasetum caquetense was recorded in the Amazonian region of Caquetá, bringing the total to eight known species exclusive to that department.

THE CASE OF Catasetum ochraceum IN THE FARALLONES OF CALI

A 2020 study conducted in the Farallones de Cali (Valle del Cauca), near La Vorágine, monitored 50 wild individuals of Catasetum ochraceum over four years. By observing their reproductive cycle, researchers confirmed that the flowers depend exclusively on male euglossine bees for successful pollination. The study recorded 18 individuals representing 8 Euglossini species: Eulaema nigrita, Exaerete smaragdina, Euglossa despecta, E. ignita, E. modestior, E. tridentata, E. deceptrix, and E. liopoda. Despite the diversity of bees observed, only Euglossa deceptrix and E. liopoda were found carrying pollinaria from C. ochraceum, thus confirming them as the effective pollinators for this orchid population.

A troubling finding from this study was that, despite the presence of these pollinators, none of the marked flowers produced fruit. Researchers suggest factors such as low visitation frequency or infertility might indicate a possible population decline. However, as seen with other orchid species, deforestation and illegal extraction are genuine threats to the survival of Catasetum, underscoring the need to strengthen conservation strategies.

A VERY BENEFICIAL INTERACTION

In recent years, at several closely located sites—from Dapa (a village within Yumbo municipality, close to Santiago de Cali), through our home garden in the city, to the Montañuelas area (situated at a higher altitude but still within the same region)—we've observed the behaviour of various bees of the genus Euglossa.

Since no collections or captures have been made, it's challenging to identify the exact bee species, yet the behavioural pattern remains consistent: bees approach, attracted by fragrances released by the flowers of Catasetum ochraceum, hover around, and repeatedly visit those flowers that have not yet discharged their pollinia. With specialized "brushes" on their front legs, they gather oils and fragrances, transferring these substances in flight from their front legs to the hind legs, where they are stored. They then return to the same flower or move on to another, repeating this fascinating process (Figures 13 and 14).

Figure 13. Euglossa sp. bee approaching a female flower of Catasetum ochraceum to collect fragrances. Photograph taken in Cali, Colombia.

Figure 14. Male Euglossa sp. gathering aromatic fragrances with the brushes on its front legs from a male flower of Catasetum ochraceum. Photograph taken in Cali, Colombia.

While bees remain on the outside of the flower, their only interaction is gathering fragrances. However, when they enter the interior and touch certain sensitive structures, the pollinium is forcefully ejected by a catapult-like mechanism and attaches itself to the bee's back (Figure 15). Startled by the sudden impact, the bee typically flies away immediately and avoids returning to these male flowers (Figure 16).

At this stage, the bee searches for female flowers, which—as seen in previous images—have a distinct appearance. Here, the bee again gathers aromatic substances, and upon entering, it deposits the pollinium into the flower’s stigmatic openings, thus completing pollination. What does the bee gain from all this? Those precious aromatic fragrances essential both for attracting mates and marking its territory.

Figure 15. Male Euglossa sp. desperately attempting to remove two pollinia adhered to its back after visiting two different Catasetum ochraceum male flowers.

Figure 16. Male Euglossa sp. in flight with a pollinarium from Catasetum ochraceum adhered to its back. Most of the time, this remains merely a temporary annoyance.

This complex mechanism has evolved in such a way that both the bees and the orchids benefit significantly. Even though the bees may carry one or two pollinia attached to their backs, they suffer no lasting harm, as these pollinia eventually fall off, allowing them to continue their activities normally. Thus, a mutualistic relationship is established, playing a key role in the ecology of tropical forests.

FINAL THOUGHTS

Interactions between plants and pollinators can achieve levels of complexity far beyond what a casual observer might suspect. The example of bees from the genus Euglossa and orchids from the genus Catasetum illustrates this perfectly. Far from being a simple exchange of pollen and nectar for pollination services, this mutualistic relationship involves a sophisticated interplay of fragrances, pollinaria, and precise rewards benefiting both parties. This highlights how evolution and co-evolution can produce highly elaborate mechanisms to ensure mutual advantage.

Some sources describe orchids as “masters of deception” toward their pollinators, yet in this particular case, both species clearly benefit: the bees collect the fragrances essential for courtship and territory marking, while the orchids guarantee their pollination through the attachment of pollinia.

Moreover, it’s surprising to discover that many of these interactions occur not only in remote forests but also in semi-rural and even urban environments. All it takes is a moment to slow down the fast pace of our lives and observe carefully. The biodiversity found in our gardens, parks, and urban outskirts can yield fascinating discoveries just like this one.

Francisco López-Machado

Biologist, Entomologist, and Nature Photographer

Cali, Colombia. March 2025