16 – Life in dead wood

At first sight, a decaying trunk that lays on the ground does not show signs of life. But if we look under the bark, into the rotting wood, we will see an unex-pectedly rich world inside. Swarms of small creatures are busy, in order to turn organic materials back to the cycle, providing nutrients that are accessible to plants. Fungi are the first decomposing organisms that appear. Their thin hyphae weave through the wood inside, constantly decaying the dead timber.

Under the bark of a dead wood we can find many arthropods: for some species it is a food source, and provides hiding place for others. Earthworms, woodlice, millipedes help decomposition processes, while centipedes, earwigs, and ground beetles use decaying trunks to hide. Many insects are known whose larvae develop in decaying wood, and participate in decomposition by chewing. Examples include longhorn beetles and rose chafers, and the European stag beetle.

The life cycle of beetles is known as a complete metamorphosis. It has 4 stages: egg, larval, pupal, adult.

Alpine longhorn beetle could even be the heraldic animal of beech forests. (Author: IvanHabiprot, source: Wikimedia Commons, licence: CC BY-SA 4.0)

There is a luminescent earthworm that lives in humid forests. It spends its life under the bark of decaying trees. When disturbed, it produces a luminescent liquid in its body, resulting a green light in the dark. (Author: Tímea Szederjesi PhD, source:mmtmuzeum.blog.hu)

Woodlice belong to decomposing organisms. When disturbed, they roll up into a small ball, and even hide their tentacles.

Common pill woodlouse. (Author: Walter Siegmund, source: Wikimedia Commons, licence: CC BY-SA 3.0)

Common pill woodlouse, rolled into a ball. (Author: Franco Folini, source: Wikimedia Commons, licence: CC BY-SA 3.0)

Under the bark of decaying trees we can usually find millipedes, that feed on organic debris. Unlike their name, they have much fewer legs, just about one hundred. It looks like more because there are 2 pairs of legs per segment. If a millipede feels threatened, it curls into a spiral. (Author: Ryan Hodnett, source: Wikimedia Commons, licence: CC BY-SA 4.0)

Centipede is a carnivore insect, preying on smaller arthropods. It is active at night, and spends daytime mainly in its hiding place. If you disturb it, it quickly looks for a new cover. (Author: AfroBrazilian, source: Wikimedia Commons, licence: CC BY-SA 4.0)

Earwig - contrary to its name - does not settle in man’s ear. It feels more comfortable in dark and humid places, like under the bark of decaying trees. When it feels danger, it emits a foul-smelling liquid. Looking at the pincers on its abdomen, you can also tell the sex of the insect: males have much more corved pincers than females. It is an omnivorous insect, sometimes eats dead arthropods, too. (Author: Francisco Welter-Schultes, source: Wikimedia Commons, licence: CC0 1.0)

The blue ground beetle is a protected insect in Hungary. It is a carnivore species, but harmless to humans. If you find one, it is not recommended to catch it: it pulls out a foul-smelling liquid, difficult to wash off. (Author Marcell Kárpáti, source: izeltlabuak.hu, licence: CC BY 4.0)

Due to their specific habitat needs, one fifth of the so-called saproxylic beetles (that feed on decaying wood) are threatened with extinction in Europe!

Did you know?
The red flat bark beetle spends nearly all its life under the bark of decaying trees. Due to its flattened shape, it can easily move in these narrow places. The larva feeds on decomposing wood, and undergoes more years of development. Interest-ingly, the beetle has some kind of natural ’antifreezer’ in its body, thus the imago can easily hibernate and then just thaws in spring.