The Orchid, the Bee and the Brazil Nut Tree….

…and the agouti….and the frog

When I was a child in the early 1960s the only time we saw Brazil nuts was at Christmas time. My brothers and I would try to crack the hard outer cases, mostly unsuccessfully, with the hand-held metal nutcrackers of the time. Eventually the only way to gain entry to the flesh beneath was to use a hammer. The result was usually a pile of smashed nut mixed with fragments of rough brown shell, and totally inedible. My father was the only person in the household to eat them, and incidentally the only person in the house able to successfully extract the nut from its virtually impenetrable shell, and we would be scolded for giving them the ‘hammer treatment’ because Brazil nuts were expensive, hence them only being purchased at Christmas. The only other member of the family to enjoy Brazil nuts was my grandparents’ African grey parrot. We were always fascinated by his ability to crack this nut. It was Polly’s party-piece. He would hold the nut in a foot and delicately turn it this way and that with his beak, eventually choosing a place, perhaps a weak point, where he would begin to peel back the hard outer case as if peeling an orange. It didn’t occur to me then where the nuts came from. They just appeared on the greengrocer’s shelves around Christmas time and disappeared shortly after.

Had I known then how these ‘nuts’¹came to be on the greengrocers’ shelves I would have understood why they were so expensive, and the process would have amazed me. As it does to this day. Firstly the nuts are almost exclusively produced by ‘wild’ trees in pristine rainforest (reasons for which will become clear) that are both protected and harvested by local indigenous people and provide them with an important income. However, before that can happen a quite remarkable series of events has to occur.

High in the canopy of the Brazilian rain forest an iridescent green jewel flashes through the leaves. An oil bee². He flies fast. He needs to, because the precious cargo he carries is coveted by others of his kind who would attack and rob him of it.

He has spent many hours arduously scraping the petals of numerous specific orchid flowers to collect the aromatic waxy oils they produce and storing them in special pouches on his hind legs. These orchids produce no nectar with which to entice a pollinating insect. Instead they produce aromatic oils to attract these specific, and only male, bees to do the job for them³. Female bees are not attracted to these orchids. The plants are epiphytic, and live high in the canopy attached to the rainforest trees. Their nutrient sources are limited to those that dribble down the bark of the tree, or from small pockets of detritus which accumulate in the crevices and hollows. Nectar and pollen are both expensive things to produce. Nectar is basically made of sugar, a precious resource which the orchid also needs to build its body, so it keeps that for itself and does not waste it offering it to any passing insect that may or may not render a pollinating service. Neither do they profligately dust their pollinators with pollen. Much would be wasted this way, and no guarantee that any of it would find its way to another orchid of the same species. Instead, the orchids have found an ingenious way to ensure that their pollen reaches the correct target. Oil bees are large and robust creatures. They need to be, for they have to negotiate and force their way into the complicated orchid flowers to find their oily reward. Each species of orchid has its own unique mechanism in its flowers, which glues small packets of pollen (called pollinia) onto the bee’s body as it makes its way out of the flower. Each species of orchid will place the pollinia onto a different part of the bee’s body, head, thorax, or abdomen. It then has another mechanism to remove the pollen from only this part of the body when the bee enters another flower of the same species, thus ensuring that only pollen from the same species will be transferred.

The shiny green bee, sporting a fancy head-dress of two bright yellow pollinia, has not only collected the waxy aromatic oils from orchids, but also from other smelly sources such as rotting flesh and faeces⁴, and with his own pheromones. This mixture is stored in special pouches on his hindmost pair of legs. He has mixed all these substances together to concoct his own unique perfume for a very special purpose. He flies directly to a particular location in the forest, and comes to rest on a clear patch of bark of a favoured tree. Other male bees of his kind are here, and he has to defend his favourite spot. He flies in tight circles around intruders until they leave. He starts to display, hovering and wing-buzzing. Presently female bees arrive⁵. His activity intensifies, the wing-buzzing perhaps distributing his unique perfume. Finally a female approaches him and inspects his perfume baskets with her antennae. Satisfied that he is the perfect partner, she mates with him.

Now the female bee needs to find food for herself and her future brood⁶, as well as a suitable nest site. She zig-zags through the forest, searching for a place safe from predators and parasites which would threaten her offspring. She finds it. Underneath a loose piece of bark. A space, a hole, dry and hidden. There is room here for several brood cells. First she collects mud from the banks of a puddle on the rainforest floor. With this she constructs a wall around the cavity under the bark with a small entrance hole just big enough for her to enter. This done, and safe within, she starts to build the brood cells. She collects more mud, forming and shaping it with her mandibles into small cylinders sitting vertically on the floor of the hole. All this takes energy and she often breaks from the building effort to seek out nectar from the flowers of the forest to fuel her body. Once the cell is complete she lines it with resin collected from the oozing sap of trees. Then she seeks out pollen as well as nectar and mixes the two into a sticky mass which she pushes into the cell, before laying an egg on top. The hatching larva will have enough provisions to see it through to pupation and emergence into adulthood, safe inside its almost impenetrable cell. The cell is then capped with more resin. All this takes the industrious bee three to four days to complete just the one cell. She will then go through the same process again and again until three to five cells are complete.

During this process she will visit many forest flowers for nectar and pollen including those of the Brazil nut tree (Bertholletia excelsa)⁷. The long-lived tree exists as isolated individuals, and is one of the largest and tallest trees within the Amazonian rainforest⁸. She has to force her way into the large creamy-white flowers under a protective hood which, together with the petals, form a chamber which contains the stamens, stigma and nectaries. Only a large strong bee is able to force its way into this chamber to gain its nectar reward. While inside the chamber she becomes liberally dusted with pollen, which is then transferred when she visits another flower.

Thus pollinated, more than a year must pass before the fruits mature. The large (up to 15cms in diameter) woody capsule contains 24 large seeds – these are the familiar Brazil nuts. But the story does not end here.

In order for the Brazil nut tree to persist in the rainforest some of its seeds have to be dispersed and buried in order to germinate. The seeds are contained in a large, round, very hard and almost impenetrable woody capsule that remains intact when it falls to the ground. They must wait for help.

It comes in the shape of a large rodent – an agouti. The capsule has a small hole at one end which is just the right size for the agouti’s teeth to get a purchase. The animal gnaws through the capsule and the seeds are released. He eats some of the nutritious seeds, but what is more important for the survival of the trees is that he buries some in caches for the lean times. The agouti is the main distributor of Brazil nut seeds – almost exclusively. Although some capuchin monkeys can break open the capsules by hitting them onto a stone anvil they do not bury the seeds as the agouti does. Animal and tree have evolved a mutually beneficial relationship together over many thousands of years. It’s quite possible that the tree has evolved such a hard and impenetrable seed capsule precisely because it needs the agouti to bury its seeds. No other animal, aside from humans and the aforementioned capuchin monkeys, appear to be able to open the capsules, and then to bury the seeds.

The Brazil nut tree is a slow breeder. It lives many centuries and takes decades to reach maturity and breeding condition, and the production of seeds (Brazil nuts) is a slow process. Even when the seed germinates the young tree may have to wait years for a gap in the canopy to provide it with enough light to grow. All conditions have to be aligned and in place for the tree to be able to produce the nuts. It is for this reason that Brazil nuts are not generally successful in plantations, and those that are must be surrounded by natural rainforest, and its pollinators, in order to produce a viable crop. So the majority of the nuts found on your supermarket shelves are harvested from intact ancient rainforest, tree by individual tree. The tree is part of a complicated web of life that it is supported by and it supports in turn. If the rainforest ecosystems become degraded and even one of the species that make up its complicated support network are lost then the Brazil nut will go too, along with the many other species that also call the trees home, as well as the indigenous peoples who rely on it for their livelihoods. If the special oil-bearing orchids disappear then the male Euglossine bees may not be able to attract females and so the species, unable to breed, will be lost. If there are no female bees to pollinate the Brazil nut tree then no nuts will be produced, and these trees will eventually become extinct, although individuals may persist for centuries there will be no new trees to replace them when they die. While the agouti can and does seek out other sources of nutrition for itself, it is vital for the distribution of the Brazil nut tree throughout the forest. Again, without this mammalian link in the chain the Brazil nut will be lost.

The loss of this small tasty item from our diets does not seem to be of very great importance. However, it is just an illustration of the complicated web of life that supports the whole planet. We mess with it at our peril. The Brazil nut can and does have far greater parts to play within the ecosystem that it inhabits than I have shown you here, most of which we cannot even begin to imagine or understand.

Lastly, in 2009 researchers in the Amazonian rainforest of northern Bolivia discovered a new species of frog⁹ that almost exclusively reproduces in the discarded empty Brazil nut capsules that fill with water. Whatever next….

2023

1 Brazil ‘nuts’ are not true nuts, such as hazel nuts. They are actually very large seeds, which are produced on the tree encased in a large hard, woody capsule which falls to the ground when ripe.

2 Large bees of the Family Euglossini.

3 Orchids of the genera Stanhopeinae and Catasetinae are pollinated exclusively by male euglossine bees.

4 Each species of bee collects fragrances from the same suite of specific sources.

5 Euglossine bees are difficult to study given that they live high in the rainforest canopy. There is no evidence at the time of writing as to how the female bees are attracted to the males, whether by scent, sight and/or sound, and to whether the display behaviour is for the purpose of attracting females or for male-male competition. It has also been suggested that females will choose a male on the basis of the quality of his perfume, but there have been no experiments as yet to test this hypothesis. The behaviour described here, therefore, is just one possible scenario.

6 Euglossine bees are solitary and do not live in large colonies or make honey.

7 While many insects and even birds visit the flowers of this tree, it relies upon only a few genera of large robust bees, including oil bees, for pollination.

8 A mature Bertholletia excelsa will reach 50 metres and may live for 500 and possibly up to 1000 years.

9 Osteocephalus castaneicola