Nature 2019 December

Peculiar habits

Transformations and
metamorphoses

Plants and animals have evolved infinite ways of affording themselves protection and exploiting opportunities over every season of the year. We largely take these transformations, adaptations or peculiar habits of wildlife for granted. This is either because such events are subtle, occurring over such a relatively long period, or take place out of our sight.

It is odds on, as one enters a wood in Autumn that, despite one’s best efforts, your footfall over leaves breaks the muffled silence. This disturbs a parliament of rooks high up in the tree-tops that express their displeasure with a cacophony of ‘caw-caws’. Looking upwards, there is just enough good light to spy the birds swapping places and come again to rest.

There is less light though for distinguishing one tree from another in a darker woodland. With almost all leaves now gone from branches, a walk in the local woodlands at this time of year does present additional challenges. Though a handy tool is a good pocket guide to British trees, it is of best use if studied before setting off as they are surprisingly difficult to interrogate within the depth of a typically dense ancient (i.e. not plantation) Chiltern wood or copse. Just because the branches are bare should not distract you from looking for clues.

Take the Ash, identifiable by its greyish smooth trunks which divide spontaneously. However, the best clues lie at the very top where large blotches of brown seeds (keys) can be seen set against the open sky long into Winter. Further clues lie at your feet, especially after a storm. Bright yellow crescent-shaped toothed leaves and grey sticks with jet-black winter buds in pairs. Contrast the Ash of Spring with its sap rising. The bark has a glint of aquamarine, its male flowers are a dense purple and there is almost a fluorescent burst of lime-green as new leaves emerge.

Like the Ash, the accidental Sycamore provides contrasting seasonal profiles. I call it accidental as it is an invader species of woodlands rather than a constituent part of an old wood by right. In Spring it is often a hesitant starter but usually explodes into purple and lime green as it strives to reach full leaf. As it goes from strength to strength the almost indistinct inflorescences produce specialised winged fruit known as ‘samaras’ in great profusion, which descend helicopter-style as Summer progresses.

By contrast, the Autumn tree has a very different look. Its leaves have turned from dull green via amber to burnt umber. Alongside the change of shades, the leaves of most Sycamore trees around here have been tattooed with a tar spot. This is caused by a fungus and this circular mark is almost a trademark feature. As leaves fall the skeleton of the Sycamore is revealed often with near perfect symmetry across its upturned boughs rising from an impressive central bowl. The final act of the Sycamore can be at best a nuisance and at worst a disaster. By this I am referring to the slime left when Sycamore leaves decompose on ‘puddled’ woodland footpaths which can produce treacherous conditions underfoot for the temporarily distracted rambler.

I have chosen deliberately two less distinguished local trees to illustrate the large contrast in colour and form revealed, which is also replicated in their own unique ways by all our trees over a single season.

In stark contrast to trees that live at least 50 but maybe well over 100 years, insects may survive only several months or only a few weeks.

The sole task of, for example, an adult male Red Admiral Butterfly (imago) is to find a suitable female butterfly of the same species to swap genes with. In the latter’s case her job is then to ensure the progeny together with food supply are deposited as an egg in a suitable location to maximise survival opportunities. This adult stage is highly complex and very specialised in form, (e.g. muscles, wings, colouration, antenna) and this requires considerable investment achieved by a very different, but also highly specialised, larval or caterpillar stage.

By having specialised mouth parts and high-powered digestive system the caterpillar is able to process the food-plant into super-rich food reserves. When the caterpillar pupates, this energy-rich material is broken down into a soup of fats, carbohydrate and chemical precursors of proteins. In a manner that is still not fully understood, from this soup the adult butterfly is reconstructed. Not only does this Red Admiral metamorphosis occur two or three times per year, but the final generation of Red Admirals either hibernates over winter or migrates south to warmer climes. This is a standard example of this change process, but every insect has its own unique approach.

When stepping back it is perhaps not unsurprising how all these individual cycles of plant and animal transformations, be it over an annual, monthly or even daily period sparked wonderment or delight amongst ancient civilisations, classical cultures, religious followers, the scientific community and, crucially, everyone who takes the opportunity to enjoy the trees, insects and everything else that is in continuous transformation across this beautiful area.