with insects react chemically with ozone, hydroxyl and nitrate radicals in polluted air, and this reaction destroys smell – as we and, more importantly, the insects know by experience. The study estimates that air pollution is effectively destroying the smell molecules emitted by plants all the time by as much as 90 per cent. This suggests strongly, as does literature and nature writing from the past, that before the Industrial Revolution things smelled almost ten times more noticeably. Scent loss must be a huge factor in the catastrophic invertebrate collapse we are witnessing. What we also need to fully grasp about the knock-on effects of the dissipation of scent molecules for invertebrates and vertebrates is that it is in their grub stage, when they eat and are eaten in vast numbers, that invertebrates play a huge role in the lower food chain. Caterpillars are one of the most important things that moths and butterflies offer the ecosystem – their grubs are food for almost everything else, and an estimated 95 per cent of nesting birds rear their young on insects and caterpillars. There is a chain of which we are barely aware, simple enough, everything working together. Scent in plants, moths, birds all intimately entangled in a reproductive cycle which we are blithely destroying. The intricate sophistication of moths’ co-dependence with night-scented plants, for example, is difficult to comprehend. Smell volatiles are particularly important in pollination by moths; expert sniffers, although they lack noses, they detect molecules of smell through antennae whilst foraging for nectar. Female moths pick up pollen grains all over their hairy heads and fertilise plants, whilst male giant silkworm moths search for virgins and have huge antennae that are feather-shaped, bristling with hairs that are so sensitive that they can smell a single molecule of bombykol, an ingredient of the female pheromone, as much as seven miles away and are seemingly able to estimate distance by its dilution. The phenomenal evolutionary achievement that this represents is dependent on an infinitesimally delicate balance between each moth and the world about it, its Umwelt. A balance which is being toppled and tampered with by mankind. The scented part of the plant Most insects, when not in search of a mate, are in search of nectar, carbohydrates which can be found aplenty, and readily absorbable, through the sugars in solution that go to make up nectar in a flower. As it contains sugar, nectar naturally smells sweet, but it is not the scented part of the flower. Pollen is not the scented part of the flower either, although like nectar it does have a smell, a good smell. It adds to the overwhelming complexity of the scent, as in the case of roses where that waxy smell we recognise is pollen. Pollen is also rich in proteins and this has come to offer another reward to the pollinator. An extraordinary thing about the genius of pollen is that it enables the genetic material to travel safely without water to the female stigma, which may be a very large distance away. All this required co-evolution of insects and flowering plants. Plants have evolved different lures to encourage specific pollinators and to keep their fidelity. Orchids have the most complex and profound co-evolutionary history with their pollinators. Our native pyramidal orchid, Anacamptis pyramidalis, for instance, has a carnation scent by day but a very foxy smell at night – spread-betting the odds of pollination.

Scented substances have almost certainly developed out of the waste products of plants’ and animals’ biochemistry. They are the by-products of metabolism. Waste products are not only useless in the living cell, they are positively poisonous.

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