The Secret Network of Nature by Peter Wohlleben

Author:Peter Wohlleben
Language: eng
Format: epub
Publisher: Random House

10

How Earthworms Control Wild Boar

IT’S OFTEN SAID that mild winters cause plagues of biting flies or catastrophic bark beetle infestations. We’ve already seen that explosions in bark beetle populations are more often caused by commercial forest practices, but I think it’s worth taking a closer look at the impact winter has on the forest environment. Severe winters are characterised by weeks of hard frosts and at least some snow cover. Everything freezes. The top few inches of the soil are rock-hard, and life out there in the forest seems anything but a walk in the park.

Let’s start by taking a look at how winter conditions affect smaller animals. Insects exploit the laws of nature to protect themselves against freezing. They use sugars they produce naturally to create a kind of antifreeze, and they empty their gut to minimise their water content, because tiny amounts of water don’t freeze until temperatures fall far below 0 °C. Five microlitres of water, for instance, doesn’t form ice crystals until the temperature reaches -18 °C. Despite this, the youngest bark beetles struggle to survive. If it stays cold for too long, larvae pass on to insect Nirvana without seeing spring. Their lives end not because they can’t survive freezing conditions, but because water has entered their mouths and breathing tubes. Although fluids inside the larvae are protected against freezing temperatures, when the temperature falls water entering from outside their bodies freezes immediately. That’s why the little ones survive particularly well when a thick layer of snow keeps out the worst of the cold. Because adult beetles don’t have this problem – they can cope with up to -30 °C – bark beetles try to avoid breeding in autumn.

Yet mild winters are catastrophic for bark beetle larvae, too, because mild means damp. Think about it. What kind of weather would you prefer to be out in? A few degrees above freezing in the rain or a few degrees below freezing in the sunshine? I, for one, would prefer the latter. If temperatures are below freezing, you usually stay dry, which means it’s easier to keep warm. Above 5 °C, moisture-loving fungi become active again. They get to work on the overwintering insects and start eating them while they dream.

Whereas overwintering bark beetles sit tight and wait for spring, most mammals are awake and active in winter, which means they need to eat all the time to maintain their body temperature. This puts them in the same predicament as the birds. So shouldn’t we take pity on our four-legged fellow creatures too, and feed them? In fact, we’re already doing that, at least with some species. Have you ever seen a fodder rack in the forest? Or perhaps a couple of wooden boxes filled with feed corn? This food is supposed to help starving roe deer, red deer and wild boar survive the winter. But this supplemental feeding is not an act of altruism. The provisioning only benefits animals whose antlers or tusks would look good displayed as hunting trophies above the living-room sofa.

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