Invertebrates
Fig Wasp
Blastophaga psenes · also called fig wasp
The fig wasp is barely the size of a pinhead, lives for a day or two as an adult, and cannot reproduce anywhere except inside a fig. In turn, most of the world’s 900-odd fig species cannot be pollinated by anything except their own particular wasp. It is one of the tightest partnerships in nature — and it means that a fig, biologically, is a flower with a wasp inside it.
Overview
Fig wasps live wherever fig trees grow, throughout the world’s tropics. They are 1–2 mm long; the winged females are dark and slender, and the wingless males are pale, blind, and grub-like, never leaving the fig they hatched in. The larvae eat gall tissue inside the fig.
A flower turned inside out
What looks like a fig fruit is a hollow ball lined on the inside with hundreds of tiny flowers, with one narrow entrance. The wasp is the only route pollen can take to reach them.
One tree, one wasp
Most fig species are pollinated by a single specific wasp and no other — an extreme case of two organisms evolving together so closely that neither can breed without the other.
A one-way trip
A pollen-carrying female forces through the tiny entrance, often losing her wings and antennae, pollinates the flowers, lays eggs in some, and dies inside. Her wingless sons hatch first, mate with the still-encased females, cut an escape tunnel, and die; the winged daughters gather pollen, leave, and fly off to find another fig.
Do you eat the wasps?
In a pollinated fig the female’s body is broken down by an enzyme, ficin, before the fig ripens. Many commercial figs are varieties that ripen without pollination and contain no wasps at all.
Fig Wasp: common questions
Is there a wasp in every fig I eat?
Usually not in the figs sold in shops. Many commercial figs are varieties of the common fig that have been bred or selected to ripen without pollination, so no wasp ever enters them. In figs that are pollinated the normal way, a female wasp does die inside, but by the time the fig is ripe her body has been broken down by ficin, an enzyme the fig produces that digests protein, so there is no recognisable insect left, only nutrients absorbed into the fruit. Wild figs eaten by animals do contain the remains of wasps and their offspring, which is part of what makes them nutritious.
Why can a fig only be pollinated by one kind of wasp?
Because the fig's flowers are sealed inside a hollow structure with a single entrance that is tightly matched, in size and shape and often in chemical scent, to one wasp. A wasp of the wrong species usually cannot get in, or cannot reach the flowers with its egg-laying tube, or is not attracted by the scent the fig releases when it is ready. Over millions of years each fig lineage and its wasp lineage have adjusted to each other in lockstep, a process called coevolution, to the point where the two are effectively a single reproductive unit. A few figs share wasps or have more than one, but the strict one-to-one pattern is the rule.
What do the wasps get out of the deal, and do figs ever cheat?
The wasp gets a protected nursery — some of the fig's flowers become galls in which its larvae develop, fed by the plant. The fig gets pollination. But the balance is policed. In many figs, flowers with a short style are within reach of the wasp's egg-laying tube and become wasp nurseries, while long-styled flowers are just out of reach and are only pollinated, producing seeds and no wasps. Some fig species take this further, letting a wasp enter and pollinate but preventing her offspring from developing, so the fig gets seeds for free. If wasps are too greedy and lay in too many flowers, some figs abort the whole structure, killing the brood.
How long does a fig wasp live?
Very briefly as an adult. Development inside the fig, from egg to emerging adult, takes weeks. But once a winged female leaves her birth fig she is racing against time, because she does not feed meaningfully and her body reserves are limited. She typically has only one to two days to find another fig tree that is at exactly the right stage, guided by scent, and to get inside it before she dies. Males live even shorter lives and never leave the fig at all. This is why fig trees in a population tend to fruit slightly out of step with one another, so there is always a fig ready somewhere for the next wave of wasps.