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Station 8: Living soil

General information

Over the years, the leaves and needles that fall from trees, as well as the deadwood of fallen trees should pile up to massive heaps, but this is not the case. Tiny lifeforms live off of these things. Dive into the biological diversity of this microcosm of insects, and learn something about how they live.


More informations:

  1. Insect-Hotel
  2. Insects in the forest
  3. The Habitat of the Forest Floor


1. Insect Hotel

An insect hotel provides insects with a place to nest and accommodations for the winter. In order to lure many different types of insects,  it is important to understand the partialities of the insects that one wants to attract. Here it is very important to mention that only untreated and pesticide-free materials should be used in constructing an insect hotel, and that the hotel should be set-up in a place that is sunny, but protected from wind. A great many substances are suitable as filling materials, basically anything that one can find in the woods: rotten wood, tree trunks, grasses, leaves, blossoms, herbs, bark as well as stones, loam, and much more. There are no limitations placed on your imagination other than this: the materials should reflect the natural habitats of the insects you want to attract, and the materials you use should be dry so as not to decay. In forestry there is a differentiation made between useful creatures and pests.  

A very welcome guest is the lacewing. Its usefulness is based on its appetite for aphids, spider mites, and small caterpillars. In order to attract the lacewing, it may be a good idea to build a “lacewing box” that is painted red on the front side. This is a colour that attracts the lacewing. Small slits should be cut into the front of the box so that they can enter the interior, which should be filled with straw.

In hollow tree trunks or clay tubes, one can assemble branches from various plants, alternating between hollow and closed branches. Among other insects, various species of bees are attracted to such structures. The mason bee needs hollow stems that are filled with nutrients (e.g. a blackberry branch). However, it is not just hollowed-out tree trunks that are useful, whole trunks are also useful. Pieces of birch are very easy to bore into, and provide a place for leafcutter bees and other wild bees to raise their larvae and overwinter. Many wild bees need special protection as they are on the red list for endangered animals. When selecting your tree trunks, attention should be paid to finding trunks that offer a diversity of structures, and variances in width, age, tree type and state of decay. Gaps between the trunks can be filled with straw, where earwigs like to nest. Whereas leaves and dried twigs can be used to attract ladybugs [Gartenakademie Rheinland-Pfalz].


2. Insect in the Forest

Insects perform an important role in the forest ecosystem. Individually they rank among the smallest representatives of the forest, but in terms of their sheer number, they represent the largest contingent. In terms of the amount of species, this class contains the most in the entire animal kingdom. At present there have been over a million different species scientifically documented. The differences in their form parallels the differences in the functions they fulfill in the forest ecosystem. They are useful in terms of pollination, humification, and also provide nutrition to other animals. The forest provides an incredible variety of habitats. There are insects that specialize in living off of deadwood, while other insects prefer bark or the space between bark and wood. Here a distinction can be made between insects that breed in bark and those that breed in wood.

If forestry encroaches too intensively into the forest there can be considerable consequences for the habitats of the insects. If deadwood is removed too early, many species lose their nesting possibilities. There is a direct correlation between the amount of deadwood and the level of biodiversity. Pruning can also help augment this level. Deadwood includes dead branches of a tree or an entire dead tree, or parts thereof. There are not only species that derive their nutrition directly from dead bark or wood, but also insects that are for some stage of their life dependent on coarse woody debris. An example from the species that rely directly on the wood and bark for their sustenance would be the longhorn beetle. Other insects are referred to as secondary colonizers; they use the holes and passages that wood-eating insects have bored out as a place to breed, and don’t feed off of wood. An example for this type of insect would be one of the many varieties of wild bees. Certain fly and mosquito larvae subsist in the bored out passages on growing mushrooms, or local bacteria, dead material and insect dung. Bracket fungus on dead wood provides a niche for specialized beetles and flies.

Another important group is made up of the predatory and parasitic insects that live off the animals that live in the wood.

Each phase of decomposition in the dead wood attracts certain insects. Only when the wood decays, does it spread out its debris onto the ground. At this stage the insects of the forest floor take over the task of decomposing the wood. Worms, snails, isopods and insects eliminate the remains of the decaying wood. Without the help of the insects, this decomposition of the wood would last twice as long, because the boring of the insects and the breaking down of the protective bark allow for fungi and bacteria to penetrate the dead tree. Slowly growing softwood trees such as poplars and willows are often cut down early, as they do not present any real benefit. The caterpillars from certain butterfly types use these fallen softwoods as “nurseries” [Der deutsche Wald kann mehr als rauschen] [].


3. The Habitat of the Forest Floor

The forest floor is a complex fabric, and serves as a type of “handling site” for water, food and contaminants. Additionally, the forest floor offers a habitat to many different organisms. In the topsoil (0-30 cm) of one hectare, one can find 25 tons of soil-dwelling organisms. In the soil, the species biodiversity is higher than above the ground line. In a teaspoon full of forest soil, one can find around 100 million bacteria cells, 60 km of mushroom threads, 30,000 single-cell organism, and 1,000 roundworms. These organisms are responsible for debris decomposition, humification, and the subsequent delivery of nutrients. Here there is a complex interplay between physical, biological and chemical cycles. Although one cannot see much with the naked eye, the forest floor and the activities that it hosts, is very important. Without it there would be no forest at all, as the forest floor is the foundation for all life in the forest [Zechmeister-Boltenstern 2009:20 – 22].