How to think kindly about wasps
Most people don’t like wasps. They tolerate bees because they’ve been given a good rap, but wasps! Well, they are something to fear and to eliminate. There are thousands of different types of wasps, and this is the story of just one small unnoticeable wasp which lives a complicated life in a relationship with fig trees. But before you can meet this little wasp, you need to know something about fig trees and their history.
On a remote conservation reserve tucked into the Great Dividing Range in central Queensland, there stands a massive fig tree. Thirty big men with linked hands would not reach around its girth, and its vast green canopy is held aloft by a tangle of branches some of which are thicker than the trunks of many large trees. Enid Blyton’s Faraway Tree is a dwarf beside this venerable being that has survived uncountable bushfires and floods, and the wanderings of generations of Aborigines who must have found shelter here. Standing under the tree gives a new understanding of the continuum of time, and of a contained and ancient wisdom that is hard to explain without being in its presence. As you take in its noble magnificence it becomes impossible to visualise it as a young sapling in what must have been a very different landscape in a very different time, over a thousand years ago.
This fig tree is a member of the Ficus family, of which there are about 850 different species, all commonly known as fig trees. Native to the tropics, they originated in Western Asia, where the banyan ficus, the largest of the fig species, has a revered place in the religious and symbolic life of the people, as a tree where spirits live, and as a cultural and communal meeting place under its darkly green canopy. It produces hundreds of small almost inedible seeds that are a rich and plentiful source of food for both birds and insects, thus helping to ensure the productivity of the surrounding trees, flowers and crops. The tree reproduces itself only when the seeds fall onto its own branches which grow as roots down to the ground. Over the years the roots grow into new tree trunks and ‘strangle’ the old tree.
In prehistoric times some members of the ficus family somehow migrated to the semi-warm temperate zones around the Mediterranean, where they flourished in a different form. By 4000 BC, some of these species of fig trees were being cultivated in Egypt and Arabia for their fruit, the hard seeds having somehow developed into the sweet fleshy fruit that we know today. The soft ripe fruit, celebrated as a symbol of fertility and sensuality, was a valuable and expensive delicacy, but when dried, the fruit could be easily transported, and soon became a staple element in the diet of both rich and poor people across the region.
The fig trees in Asia are evergreen. Their leaves are elliptical in shape and thick and glossy. The fruiting fig trees that we know today are deciduous and have lighter, brighter green leaves that are broader than their eastern cousins, almost oval in shape, with indents and curves that throw an interesting shadow. Although they have become a cultivated species, they can grow individually in almost any soil conditions, so there is a plentiful supply of different species of wild and cultivated fig trees across the western world.Maybe there is a fig tree near where you live. If there is, you might have observed something odd about your local fig tree. Look at it carefully as Spring begins to bring life and flowering to your garden.
And you might notice something strange. Unlike most plants and trees, the fig tree produces no flowers. In winter the branches are bare, and at the first signs of spring activity, hard little green bobbles shaped like small figs develop before the first leaves on the end of each bare branch or twig. The absence of flowers means that it won’t attract birds or bees, so that the fruit won’t grow and develop in the usual way. If there were flowers, the bees would be buzzing from flower to flower seeking nectar. In the process they would collect pollen from the male stamens on one flower and deposit some of that pollen on the female pistil of another flower, causing fertilisation to take place. Once fertilisation has occurred, a fruit develops in which the seed for the next generation of the plant is formed.
So, without the usual mechanisms in place, how does the fig tree manage to reproduce and also deliver delicious ripe fruit to eat?
It has cunningly found a way. And this is what happens.
The green nobble that forms on the end of each branch is an inverted flower, known as a syconium. If you cut it open, you will notice it is packed with tight clusters of tiny flowers. You can’t see them because they are so small, but there are both male and female flowers in this intricate construction. No bee could pollinate here. It needs a pollinator specially adapted to work within this constricted arrangement. A fig wasp.
The queen fig wasp is very small. She can just fit through the pinprick hole at the top of the fig, although she most likely loses her wings and antennae as she enters. This does not matter as she won’t fly again. As she moves around the chamber she sheds the pollen that she has picked up from the fig where she was born, and this will fertilise the fig’s ovaries, so the syconium will change and ripen into a fig. But the wasp’s primary goal is to lay her eggs. As soon as the eggs hatch, the queen fig wasp dies and her body is consumed by the fleshy inflorescence, providing extra nourishment for the ripening fruit. The hatchling wasps are both male and female, and they mate immediately. Then the females busy themselves collecting pollen from the flower clusters, while the males who are born without wings must spend the first and final moments of their lives hollowing out a passage to the outside of the fig so that the female wasps can escape. The females will emerge as queens, with wings, and they will fly about seeking to enter another syconium, to pollinate another fig, and lay their eggs and die.
And so the cycle continues as long as there are fig wasps and fig trees, because each is vital to the other. Biologists call this dependence ‘coevolution’, where the fig tree relies on the wasp for the fertilisation of its fruit and its own continuation through the development of a new seedling when the ripe fruit falls to the ground. It is a powerful example of the biological notion of coevolution, where a plant and an insect live merely to provide for the other, as host and parasite respectively. Each species of fig tree is only attractive to one particular species of fig wasp, and their dependence is absolute, so that the extinction of one species will cause the death of the other. If the fig tree near you only develops green nobbly synconia and no fruit it means that the particular fig wasp associated with it does not exist anymore, or at least not in the practical vicinity of the tree.
In another twist in this strange story, the fossil of a wasp that lived in the time of the dinosaurs was recently discovered in north east Brazil by a paleoentomologist, Sam Heads, of the Illinois Natural History Survey. The fossil has been dated as being 115 to 120 million years old, and has been classified as belonging to the extensive family of wasps which are parasites on other insects, spiders and some plants. On further examination, the wasp’s ovipositor, which is the organ through which it lays its eggs, was seen to bear a strong similarity to that of the present day fig wasp. The problem for the entomologists and the ecological biologists is that this wasp must have been alive about 65 million years before fossil records show any occurrence of figs. This turns conventional theories of coevolution upside down, because it has always been assumed that a particular host plant already has the attributes that attract a particular parasite. However, this scenario suggests that the parasite might well have been the instigator for the development of a host plant to suit its own purposes.
This story of the fig wasp is just one of many stories that show we have much to learn about the ecology and co-dependence of plants and insects. We must discover the links between them before these fragile networks are broken forever, since we don’t yet fully understand the significance of the role these webs of life play in our own existence.
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