Bark beetles are destroying Germany's forests with unprecedented speed. Fighting it becomes a mammoth task for forest owners and gardeners with trees. Find out compact facts about the appearance and lifestyle of common bark beetle species in Germany in the profile. Read here how to recognize an infestation and how to act correctly.

There are different types of bark beetles, but they all cause similar damage

Table of Contents

Show all
  1. the essentials in brief
  2. What are bark beetles?
  3. Species, appearance, way of life
  4. Which trees?
  5. Detect bark beetle infestation
  6. Bark beetle control in the garden
  7. Bark beetle prevention tips
  8. frequently asked Questions

    9. the essentials in brief

    • Bark beetles are 2-8 mm large, brown-black insects that burrow into the bark of coniferous trees to reproduce and feed.
    • Bark beetles attack spruce, pine, Douglas fir and larch. Drilling dust, small holes and resin are indications of a bark beetle infestation.
    • Cutting down an infested tree is the best way to combat it in the garden. Killing bark beetles with home remedies, insecticides and pheromone traps has no chance of success in the home garden.

    What are bark beetles?

    Both larvae and adults cause damage

    Bark beetles are 2 to 8 mm large, brown or black insects from the weevil family. The beetles bore through the bark of coniferous trees to reproduce and forage. There, larvae and adult bark beetles cause serious damage to the bast tissue, which is vital for the tree.

    Infested trees defend themselves against a bark beetle plague with resin, but in most cases die within a short time. Bark beetles are feared forest pests. In a beetle year with mass reproduction, huge areas of forest fall victim to the eating machines.

    Bark beetles - species, appearance, way of life

    More than 6000 bark beetle species colonize our planet. Of these, 110 species are native to Germany, most of which lead a hidden life and do not cause any damage. When bark beetles are mentioned in German-speaking countries, they primarily mean book printers and copperplate engravers, who leave behind a picture of devastation in forests, parks and gardens. Two other species are taking advantage of global warming and also contribute to the bark beetle's bad reputation. The following list provides an overview of the four most common species in Germany:

    bark beetle species printer engraver pine bark beetle forest gardener
    size 4.5 to 5.5mm 1.6 to 2.9mm 5.5 to 8.2mm 3.5 to 4.8mm
    color dark brown copper colored to reddish brown medium to dark brown black-brown
    body shape cylindrical, broadened at the back cylindrical cylindrical cylindrical, broadened behind
    Special feature Elytra crash dentate reddish-brown, serrated elytra dentate elytra margins dotted elytra with bristles
    Scientific name Ips typographus Pityogenes chalcographus Ips sexdentatus Tomicus piniperda
    Another name eight-toothed spruce bark beetle six-toothed spruce bark beetle twelve-toothed pine bark beetle Great Forest Gardener

    All bark beetle species on this list have an armored body. In the case of the book printer, copper engraver and pine bark beetle, the armored pronotum protrudes over the head so that it cannot be seen from above. The spherical head of the beetle can only be seen in the forest gardener. Although bark beetles belong to the weevil family, a snout is only rudimentary or has disappeared completely. The way of life of the four protagonists is examined in more detail in the following short portraits:

    Book printer - way of life

    The letterpress has a dark brown color

    Book printers maintain a sophisticated lifestyle with record-breaking reproduction rates. When temperatures exceed 16 degrees in spring, the bark beetles in their winter quarters become lively and this year's flight season begins. With somnambulistic certainty, males find a weakened conifer, preferably a spruce, and dig into the bark. There they create a ramming chamber at the entrance to the incubator. The name says it all, because book printers practice polygamy. In fact, several females visit the rambling chamber and mate. Each female eats a laterally branching passage in the bark and lays the eggs in niches.

    Within six weeks, a bark beetle larva goes through all stages of its development up to becoming a sexually mature bark beetle. During this breeding season, the rabble eats their way through the bark non-stop. An average incubator has 40 larval burrows. If 20 females hatch from them, and they reproduce with a 50 percent success rate, their number per generation increases tenfold. Following the first flight time in April and May, there are usually two more flight times in July/August and in September. With three generations per year, a female book printer can produce up to 100,000 offspring. No coniferous tree can cope with this infestation pressure, even if it lets liters of resin flow as a defense strategy.

    The following video gives an informative insight into the success-optimized way of life of book printers:

    youtube

    Etcher - way of life

    Etchers take it a little slower than the larger printers. The flight time usually begins in early/mid-May. Males keep an eye out for young, weakened conifers in order to create a rambling chamber in the bark. Emitted scents attract several females, which eat three to six larval burrows into the bark after mating. Within a few weeks, cream-colored larvae hatch from the laid eggs, which, after a short pupation, turn into adult bark beetles.

    In July and August the vicious circle starts all over again with another flight time. With two generations per year and smaller breeding systems, the spread of the copper engravers lags behind the success-oriented book printers. This does not prevent the pests from spreading invasively in the coniferous and mixed forests of Germany and Austria. Unfortunately, copper engravers use their smaller size to open up brood chambers that are closed to the book printer, such as young spruce trees with thin bark or branches in treetops.

    Pine bark beetle - way of life

    The pine bark beetle deliberately avoids book printers and engravers when reproducing. During the flight season in April/May and July/August, the pest prefers pine trees. The finished breeding system in the bark consists of a ramming chamber and two to four mother tunnels with a length of up to 100 centimetres. The largest native bark beetle species begets correspondingly large larvae with a huge appetite for the bark and bark tissue.

    Forest gardener - way of life

    Forest gardeners like to nibble on conifers

    The lifestyle and reproduction of forest gardeners differ in many ways from the other bark beetle species on our list. Where the dark brown pests are up to mischief, secondary damage to conifers is the main concern. The following overview summarizes the survival strategy:

    • Early birds with flight times beginning at 9° Celsius
    • Reproduction: monogamous with one generation per year
    • Egg-laying: one-armed longitudinal tunnels 10 cm long in the bast of freshly felled or dying pines, spruces, larches
    • Diet larva: bast and bark tissue, sometimes down to the sapwood
    • Food for young beetles: from August, ripening damage in one- and two-year-old shoots
    • Food for adult beetles: regeneration feeding on the young wood after the breeding season from May onwards

    Larvae, young beetles and old beetles hollow out the shoots as part of their maturing and regeneration feeding. The hollow branches break off during the first autumn storm. These broken branches are a welcome opportunity for other pests to infest the wounded tree. Butterflies are there, such as pine moths or pine hawkmoths, which deposit their eggs and start feeding the wood again by caterpillars.

    digression

    Spruce monoculture fuels bark beetle plague

    When something goes wrong in nature, people usually have a hand in it. Mass reproductions of bark beetles are no exception in this regard. In a natural forest with a healthy mixed culture of coniferous and deciduous trees, bark beetles act as welcome beneficials. The beetles diligently break down organic substances and make an important contribution to the material cycle in the forest ecosystem. Unfortunately, spruce wood is the favorite food of native bark beetle species. With the extensive planting of fast-growing spruce monocultures as timber, humans have created perfect bark beetle biotopes. In combination with ongoing global warming, explosive propagation rates are to be feared in the future.

    Which trees are affected?

    The oak bark beetle is one of the few bark beetle species that attack deciduous trees

    Coniferous trees feel the full force of voracious bark beetles because they are the preferred habitat of book printers and their fellow beetles. That doesn't mean that deciduous trees can feel safe. Lower classifications within the beetle family have specialized in various broadleaf tree species, such as the oak bark beetle (Scolytus intricatus), birch bark beetle (Scolytus ratzeburgi), or fruit tree bark beetle (Scolytus rugulosus). The following table summarizes which trees are frequently infested:

    Susceptible conifers botanical name Vulnerable deciduous trees botanical name Susceptible fruit trees botanical name
    Spruce Picea abies maple acer apple tree Malus domestica
    jaw Pinus beech Fagus cherry tree Prunus avium
    larch Larix decidua ash Fraxinus excelsior quince Cydonia oblonga
    douglas fir Pseudotsuga menziesii elm Ulmus hawthorn Crataegus
    tree of life Thuja hornbeam Carpinus betulus rowanberry Sorbus aucuparia
    juniper Juniperus Oak Quercus
    silver fir Abies alba birch Betula

    Various research projects are dedicated to finding tree species that are resistant to bark beetle infestation. A trial cultivation area in the Hochsauerland district delivered promising results. Araucaria (Araucaria), cedar (Cryptomeria japonica) and coast redwood (Sequoia sempervirens) prove to be resistant trees there.

    tips

    The Asian bark beetle, also known as the Asian longhorned beetle, has been on the rise in Germany since 1996. The introduced pest primarily targets deciduous trees such as maple, birch, poplar and apple, pear and cherry trees. Typical feeding patterns are tiny, circular holes in the tree bark and elongated larval tunnels under the bark.

    Recognize bark beetle infestation - indicators at a glance

    The sooner you find out about voracious bark beetles, the more effective the fight against them. With the beginning of the first flight time in April, please examine standing and lying wood carefully for the following indications of a bark beetle infestation:

    • Round, 1-3 mm small holes in the bark as entry and exit holes
    • Piles of drill dust on and under the tree
    • A striking number of resin drops on the bark
    • Eating pattern under lifted bark: elongated mother burrows and larval burrows branching off from them

    When bark beetles bore in, trees react with increased resin leakage. Resin droplets and resin flow trajectories can be due to other, natural causes and are not a mandatory feature of an infestation.

    Drill dust search - tips

    Drill dust can be found at the base of the tree and under the bark

    Searching for bore dust is the best way to identify infested trees in good time before adult bark beetles or young beetles fly out and spread invasively into the surrounding woods. The following tips explain how to do it right:

    • When? Weekly from the beginning of April, when bark beetles create the rambling chamber and mother tunnels.
    • Where? At the base of the trunk, behind bark scales, on cobwebs, under lying trunks and fallen branches
    • Time? In dry, windless weather, because drill dust may have been washed off or blown away.
    • Pay attention to what? Fallen green needles or leaves, stunted twigs, sprouting patches.

    If you discover pieces of bark lying on the ground while looking for drill dust, this is another indication of a bark beetle infestation. Clever woodpeckers don't stay hidden from the activities under the trunk's bark for long. On the hunt for tasty beetles and succulent larvae, the hungry birds hammer off parts of the bark.

    Bark beetle control in the garden - what helps?

    Holes in the bark and piles of drill dust leave no doubt about the bark beetle infestation on the garden tree. Hobby gardeners are now faced with the question: what to do? Chemical sprays are frowned upon in the natural garden, especially since any insecticide is ineffective against bark beetles. Experiments with home remedies come to nothing and give the pests additional time for mass reproduction in the beetle tree. Predators such as birds or hostile beetles are at a loss against thousands upon thousands of bark beetles in a single tree.

    Hobby gardeners are not at the mercy of a bark beetle plague. The only effective control method is copied from the all too battered foresters and is called "clean forest management". This technical term refers to the removal of material suitable for breeding by felling trees and disposing of them safely. How to successfully fight bark beetles in the garden:

    Fell the infested tree

    If spruce, pine and other conifers in the garden are victims of the bark beetle, only a pruning saw or an ax will help. Once the beetles have nested under the bark, they cannot be driven away. Although time is short, please contact the lower nature conservation authority in advance. There you will find out whether immediate felling is in line with the strict provisions of the Federal Nature Conservation Act and Tree Protection Statutes, or whether a special permit needs to be applied for.

    Please do not dispose of the beetle-infested wood in the compost. Bark beetles are cold-resistant and can easily overwinter in the garden as eggs, larvae or imagos, only to strike again next year. Small amounts of wood go into the bio bin. A green waste container is suitable for disposing of a large tree including its roots, or you can transport the cuttings to the nearest composting plant using a trailer.

    Pheromone traps in the garden are counterproductive

    The bark beetle infestation is detected with pheromone traps

    In the forests of Germany and Austria, the dark boxes have long been a familiar sight. Forest owners and foresters set up pheromone traps for bark beetles. These are attractant traps that are primarily used for monitoring, i.e. determining the infestation pressure in the forest. If placed correctly and in good time, the traps provide the expert with important information about the course of the swarm, the peak of the plague or subsequent generations during an observation period of several years. The catch rate of a trap is too low to make an effective contribution to combating it.

    Pheromone traps against bark beetles are unsuitable for use in private gardens. A minimum distance of one tree length to healthy trees is prescribed, which is difficult to maintain in the classic home garden. In the worst case, an attractant trap does what it is supposed to do, irresistibly attracts bark beetles from adjacent forest areas and thus shows the beasts the way into your garden.

    Anyone who puts off combating the disease will be punished by the bark beetle mass proliferation.

    Preventing bark beetles - tips for hobby gardeners

    Weakened spruces give off a special smell that bark beetles perceive with their antennae. Drought stress, nutrient deficiencies, wind and snow damage make the conifers ideal candidates for a mass propagation infestation. It doesn't have to come to that if you pay special attention to tree care in the garden. The following tips explain how to successfully prevent bark beetles:

    • Water regularly during dry periods without causing waterlogging
    • In spring and summer, fertilize trees with compost, horn shavings (32.93€) or other organic fertilizers
    • Potassium-focused autumn fertilization strengthens winter hardiness
    • Mulch the tree disc flat and clear it in the fall
    • Clear away damaged wood promptly after wind or snow breakage
    • Smooth out wounds on the wood with a disinfected knife, apply tree wax (€12.96) to the edge from a diameter of 2 cm

    Take special care when pruning spruce, pine and other conifers. Prune conifers in early spring only when needed. Limit the pruning to the green, needled shoot area. Radical pruning measures in the old wood weaken every conifer and attract lurking bark beetles.

    Attract natural enemies

    Natural enemies of the bark beetles can be found in the near-natural garden. Important predators of book printers and their ilk are:

    • Birds, especially woodpecker and raven
    • Predatory beetles, such as hunting beetles, bark beetles and ant beetles
    • Parasitoid insects, especially parasitic wasps (22.99€) and chalcids

    With a consistent renunciation of pesticides of all kinds, you invite the hard-working beneficial insects into your garden. Create retreats such as mixed hedges, natural dry stone walls, piles of leaves or a wild corner. Put up nest boxes and insect hotels. If natural enemies are already there, incoming bark beetles have a bad hand. However, the predators have no chance against an acute infestation with explosive reproduction.

    frequently asked Questions

    What do bark beetles eat?

    Bark beetles especially like to eat conifers

    Bark beetles eat wood, bark and bast tissue from trees and large shrubs. The most important food plants for the dangerous book printers are spruces, pines, larches, Douglas firs and other conifers. Other bark beetle species like to eat the wood of deciduous trees. Fresh wood not only serves as a source of food for forest pests. Furthermore, adult bark beetles eat through the trunk bark to create tunnels for laying eggs. The larvae hatch from this and feed their way merrily through the wood until they pupate and metamorphose into a sexually mature insect.

    Can bark beetles fly?

    Bark beetles are insects with a fully developed flight apparatus. The filigree wings are well protected under armour-like elytra, which are clearly toothed when they fall. Of course, the beetles don't like to take to the skies. Bark beetles only fly short distances of less than 100 meters to search for a suitable host tree. In exceptional cases, book printers and conspecifics can fly a kilometer or two, provided a strong air current provides additional propulsion.

    What does a bark beetle look like?

    Bark beetles native to Germany are 2 to 8 mm in size. The dark brown body is cylindrical to cylindrical and has a hard shell consisting of elytra and pronotum. In the case of printers and engravers, the armor extends over the spherical, downward-sloping head. The elytra fall slightly obliquely from the middle to the end. The lower side edges each have three, four or six teeth. The number of teeth gives an important indication of the species affiliation.

    Is there an obligation to report bark beetle infestations in Germany?

    No, the infestation with bark beetles in Germany does not have to be reported. In most federal states, forest owners are obliged under the Forest Act to combat pests effectively and in good time. The lower forest authorities of the districts monitor whether forest owners actually fulfill these obligations. Austria handles the threat to its forests from bark beetles more strictly. The dangerous proliferation of bookworms and other bark beetles must be reported immediately to the responsible forest authority.

    Are bark beetles a danger to our furniture in the house?

    Bark beetles are among the fresh wood insects. Dry, built-in wood is not interesting for the beetles as food or as a breeding ground. It eats wood, bark and bast tissue with active sap flow. Males and females set up breeding systems for reproduction exclusively in or under tree bark. Bark beetles pose no threat to furniture, parquet floors or roof beams.

    Can't you just kill bark beetles with chemical insecticides?

    Decades of experience controlling bark beetles in gardens have taught us that insecticides are ineffective. Sprays used in forestry are not permitted for private gardens. In any case, killing the tree pests by spraying poison has little chance of success. Bark beetles sit well protected under a thick trunk bark and are immune to all kinds of sprays thanks to their strong armor.

    We would like to plant a house tree that is largely resistant to bark beetle infestation. Which tree species are suitable?

    Tree species from southern countries come into focus as a recommended alternative to spruce. In the course of climate change, warmth-loving trees like Atlas cedar (Cedrus atlantica), araucaria (Araucaria) and Japanese cedar (Cryptomeria japonica) feel at home in Germany. Among the deciduous trees, the red oak (Quercus rubra) imported from North America is said to have good resistance to book printers and copper engravers. Other guest tree species that the bark beetles do not like are black locust (Robinia), vinegar tree (Rhus hirta) and black cherry (Prunus serotina).

    How can a bark beetle infestation be recognized?

    The infestation with bark beetles can be recognized right from the start by the discharge of brown to light brown drill dust. The flour collects at the base of the trunk, lies between scales of bark or hangs in cobwebs. Symptoms that follow later are woodpecker chips, pieces of bark that have fallen off and loss of green needles and discoloration of the needles in the crown.

    As a home gardener, am I obliged to control bark beetles on my home trees?

    No, the statutory obligation applies to forest owners within the meaning of the Federal Forest Act (BWaldG). Consequently, smaller areas with clusters of trees within built-up areas are not forest. This means that you are not required by law to cut down infested trees or to employ experts for pest control. However, it should be borne in mind that a passive, wait-and-see attitude plays into the hands of the invasive bark beetles and, in the worst case, can affect the entire neighborhood.

    tips

    Eggs, larvae or young bark beetles can still be found in the freshly cut firewood for the fireplace and stove. To prevent the beasts from nesting in the house or apartment in this way, you should store the wood outside for a period of at least two, ideally four years.

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Animals in the garden