Nature’s symbiotic relationships are as multifarious as they are marvellous

Birds do it, bees do it and fleas, educated or otherwise, most certainly do it.

‘It’, in this case, is what biologists term ‘symbiosis’, meaning a close, long-term necessary interaction with another different species. The word hasn’t strayed far from its root, the Ancient Greek symbios (living together with another) and bios (life). Symbiosis can be lovely, it can be nasty, it can be indifferent, but it made the natural world in which we live. A squillion years ago, primitive plant forms trying to get a grip on the earth of Earth got a rooting leg down with the aid of anchoring fungi. To this day, the vast majority of plants and trees — more than 90% — still rely on the thin threads of underground mycorrhizal fungi to live and to breathe, even to send chemical messages to other arborea, the ‘Wood Wide Web’. Symbiosis: it’s a long-term affair.

Nature, being Nature, exhibits symbiosis in more ways than you can shake a Power-point remote controller at. Our little grey cells conveniently reduce it to three main sorts. We’ll commence with mutualism, whereby both species benefit, either thriving together so that both win or when the one could not survive without the other. The most well-known example of mutualistic symbiosis is the relationship of the aforementioned bees with the flower and vice versa. In return for receiving sweet nectar, bees help to pollinate the plants that may have otherwise not been able to reproduce. This happens because pollen sticks to the bees’ legs when they feed; there are even bees with special adaptations, pollen ‘baskets’, on their spindly limbs to help the harvesting from, say, the wildflower-spreckled verge on the local country lane. Our human version of mutualism is incorporated in the apothegm ‘scratch my back, I’ll scratch yours’; more elevatedly, there is the Latin expression quid pro quo.

We humans rather like mutualism. If it is transactional, something for something, it also suggests societal co-operation and cohesion. Bonding as a means of survival. According to a quote often attributed to Charles Darwin: ‘In the long history of humankind (and animal kind, too) those who learned to collaborate and improvise most effectively have prevailed.’ You drive your car safely in the expectation that others do likewise.

Out in the British countryside, the examples of mutualism are as multifarious as they are marvellous. Take, for starters, a hypothetical good old meadow with ant hills strewn like grassy scatter cushions. Say this flowery mead lies alongside our bee-friendly lane noted above. Down in the very base of the yellow meadow ants’ tump, in a cellar, the mob of Lasius flavus keep a herd of aphids to be ‘milked’ (licked, in fact) for the sugar, or honeydew, they produce. A colony of yellow meadow ants can easily harvest 22lb–33lb of sugar from its aphids over a summer. In return, the aphids receive protection from predators and valeting that cleanses them of parasites. Think insect dairy-farming.

In that same meadow, there may be blue butterflies, dilettantish, flitty-floating about and likewise in a symbiotic relationship with ants, what is technically ‘myrmecophily’. The caterpillars of Adonis blue (Polyommatus bellargus), an icon of chalk grassland, exude the honeydew that ants are so delirious for — to the extent that the ants carry the caterpillars into their underground nest, where, safe, the latter pupate over winter.

In the meadow there are also starlings (Sturnidae) on the backs of sheep, picking off annoying bugs. The bird gets grub, Shaun the Sheep gets relieved of an itch, an avian-ovine symbiosis acknowledged in the old folk name for starlings, ‘sheepstares’.

Magpies (Pica pica) perform grooming duties on farm beasts, too, before flying back to roost in the alders lining the brook. The alder trees (Alnus glutinosa) fix nitrogen in the soil through a symbiotic relationship with Frankia bacteria in their root nodules, thus enriching the ground. The peas and other legumes — our future food — in the surrounding crop fields do the same nourishment of the earth, but with other bacteria. On the bark of the alder are grey clumps of lichen, which, despite appearances, are not one organism, but symbiotic relationships between fungi and algae (or, sometimes, cyanobacteria). The fungus provides the stable protective architecture, whereas the algae photosynthesis produces the life-giving energy. Together, they are greater than the sum of their parts, harmony in action. In the oak wood beyond the pea field, chanterelle mushrooms (Cantharellus cibarius) are draped like a small orange robe about the base of an oak, filling the woodland air with their apricot perfume. Mycorrhizal fungi are not random; chanterelle form a mutualistic relationship with the roots of particular host trees, primarily oak, beech, birch, pine and spruce in the UK. They are a gourmand’s delight.

Number two type symbiosis is commensalism, where one species benefits when the other does not, but the latter is not harmed in the process and is indifferent to it. It’s the graceful, brilliant-white cattle egrets (Bubulcus), an increasingly common bird in the UK, getting a free meal of insects stirred up by bovine hooves and its water fleas, Daphnia, feeding on the algae and micro-organisms stirred by grazing aquatic snails in the pond in the meadow corner. Our virtual field is also conveniently beside the seaside. Commensalism is barnacles getting a free ride on the cruising whales to nutrient-rich waters.

As the Devil has all the best tunes, so parasitic symbiosis, number three, has all the best stories in symbiosis — and all the grimmest reapers. Fleas on the shepherd’s sheepdog, ticks on the deer that live in the wood beyond the crop field, the 30in Anoplocephala magna tapeworm in the gut of the child’s pony trotting along the lane. In parasitism, derived from the Latin for ‘one who eats at the table of another’, the parasitic organism lives off a host at the host’s expense, even unto its death. The mistletoe festooning the apple tree in the orchard behind the meadow has developed special roots that penetrate the tree’s bark and tap into its water and nutrient sources.

Down in the rock pools, it’s a parasite’s delight. The isopod Anilocra physodes, a woodlouse-like thing, clamps on to some luckless fish, notably wrasse, and sucks the lifeblood out of them. Then there is its cousin the isopod Ceratothoa steindachneri, known as the tongue-biter, which attaches to the tongue of weaver fish until the tongue shrivels and falls off. Don’t forget, either, the truly macabre crab hacker barnacle (Sacculina carcini), which attaches to the underside of the shore crab, invades its body with probing fleshy rootlets, then chemically castrates it. An infected male even develops a wider, feminine abdomen, together with motherly characteristics. The hacked crab guards the parasite’s eggs, attached to its underside, as if they were its own. Welcome to the Rocky Pool Horror Show.

Symbiosis. It makes the natural world go around. We can’t live without it, but sometimes we’d rather not know the details.