Grubs - they look like fat, white caterpillars - live in almost every garden. These are the larvae of different species of beetles, some harmful and others very beneficial. In this article you will learn how to differentiate between pests and beneficial insects and how to combat the former effectively.

Cockchafer grubs can cause a lot of damage in the bed

Table of Contents

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  1. the essentials in brief
  2. What are grubs?
  3. Harmful grubs or beneficial insects?
  4. way of life and harm
  5. fight grubs
  6. What else helps against grubs?
  7. Effectively prevent grubs
  8. frequently asked Questions

    9. the essentials in brief

    • The larvae of the various scarab beetle species are called grubs.
    • Most grubs live in the ground for years, but can also be found in raised beds, flower pots or compost.
    • Not all grubs are pests, some - such as the larvae of the rose chafer or the rhinoceros beetle - are even very useful for the production of humus and are therefore welcome guests in the compost heap.
    • Harmful grubs can be combated using a variety of non-toxic methods, but they usually only become a problem when they appear in large numbers.

    What are grubs?

    Grubs are relatively large, mostly light-colored larvae

    The larvae of various beetle species from the family of scarab beetles (lat. Scarabaeidae) are called grubs. The name comes from Old or Middle High German and refers to the appearance of the larvae: It means something like "maggot" or "little worm".

    Scarab beetles are a very large family, comprising over 27,000 different species worldwide. Only a few of these occur in our gardens, and many are threatened with extinction or have become very rare. This applies, for example, to the may beetle, whose grubs could cause considerable damage and famine in earlier centuries. In the 1950s to 1960s, the animals were radically fought, so that today they are hardly to be found. In some years, however, they occur massively and can cause major regional damage.

    However, not all scarab beetles and the associated grubs can be classified as pests. On the contrary, because the larvae of the rose chafer and the very rare rhinoceros beetle (which is also a nature reserve) are considered to be extremely beneficial.

    In the garden and on the balcony you will mainly find these species:

    cockchafer June beetle garden beetle rose chafer rhino beetle
    Latin designation Melolontha melolontha Amphimallon solstitiale Phyllopertha horticola Cetonia aurata Oryctes nasicornis
    Alternative designations field cockchafer Ribbed tufted beetle - Golden rose chafer, common rose chafer -
    frequency almost extinct, meanwhile more frequent again frequent to rare depending on the region very common, widespread frequent to rare depending on the region rare, is under protection
    flight time early May to early June from the beginning of June between late May and late June April to October May to June
    size 20 to 30 millimeters 14 to 18 millimeters 8 to 11 millimeters 14 to 20 millimeters 25 to 40 centimeters
    coloring black except for legs, antennae and elytra dark yellow to brown black-green except for elytra, shiny metallic metallic shiny, green to bronze colored, underside reddish golden very shiny, dark brown to black
    elytra reddish brown three longitudinal ribs, dotted between them six longitudinal stripes on each wing, light brown white transverse grooves and spots, two broad longitudinal ribs shiny and smooth, fine dotted rows
    Special features Wings do not cover the end of the abdomen between elytra and pronotum bright central line dense hair always shiny metallic, different colors possible eponymous horn (males only)

    The beetles are crepuscular, so you will find them either in the evening or early morning.

    What do grubs eat?

    While the adult beetles usually feed on leaves, flowers or plant sap, their grubs live in the soil and prefer to eat decomposing plant material and living plant roots. The larvae of the May beetle, June beetle and garden beetle like to attack plant roots and can thus damage the vegetation in the garden. The grubs of the rose or rhinoceros beetle, on the other hand, mainly eat dead wood and other dead plant material. That is why rose beetle grubs in particular are often found in the compost. There they help to convert the plant residues into valuable compost.

    Harmful grubs or beneficial insects?

    There are grubs in every garden. The pest larvae of the cockchafer, for example, usually cause little damage, at least if they only occur sporadically. They only become a problem when they occur massively. In addition, it makes sense not to kill all the thick, white maggots at once: You should be able to distinguish those of the rose chafer and the rhinoceros beetle from the harmful species. They are very useful and should therefore be kept alive. But you can also let the larvae of cockchafers and co. live, so as not to bring the animals that have become rare to the brink of extinction - at least if you only find a few grubs.

    Determining grubs: characteristic differences

    cockchafer June beetle garden beetle rose chafer rhino beetle
    classification pest pest pest beneficial beneficial
    larval activity from the end of June from mid to late July July to October from June from June
    size up to five centimetres up to five centimetres significantly smaller than May or June beetles up to five centimetres up to 12 centimeters
    coloring yellowish white with brown head capsule yellowish white with brown head capsule yellowish white whitish whitish
    Look curved, three pairs of legs curved, three pairs of legs curved, three pairs of legs plump, curved, three pairs of legs cylindrical, curved, three pairs of legs
    Special features Pronounced abdomen divided in two by a ring-shaped furrow no division of the abdomen no division of the abdomen often in compost or rotten wood significantly larger than other grubs

    You can also use this test to tell the difference between harmful and useful grubs:

    1. Turn the grub onto its back.
    2. Larvae of the May or June beetle remain
    3. or try to move sideways by meandering.
    4. June beetle larvae usually crawl lying on their stomachs.
    5. Rose beetle larvae stretch all pairs of legs backwards in the air
    6. and move with caterpillar-like movements.

    The larvae of the rhinoceros beetle, on the other hand, can be easily distinguished from the other grubs by their sheer size.

    Recognize grubs: way of life and damage

    But what are the characteristics that indicate that there is a problem with grubs in the garden? We now address this question in this section.

    way of life and harm

    It is typical for all types of grubs that they sometimes live in the ground for up to five years before pupating. The larvae of the May beetle or the tawny beetle do not feed exclusively on plant roots - these varieties also eat plant remains and live in humus. Only after pupation do the now adult beetles leave the earth and can be seen primarily at dusk.

    While the fairly large beetles are conspicuous in the garden, an infestation with grubs is usually noticed late or by chance - for example when digging a bed. Attention is required when plants seem to be dying for no reason - often they can simply be pulled out of the ground due to a lack of roots. Then dig a little in the ground and you will find fat, white grubs there.

    digression

    These plants are particularly endangered

    Basically, almost all plant species can be attacked, grubs are not particularly choosy in this regard. However, they particularly like to nibble on the roots of young plants (especially vegetables, lettuce and strawberries), potatoes and turnips. Grass roots, on the other hand, belong to the favorite food of the larvae of the garden beetle (curle beetle), which eat entire lawns bare in the event of a severe infestation. Typically, the blades of grass dry up and can be easily pulled out of the ground - after all, the roots are missing.

    fight grubs

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    Plants that have already been visibly damaged by the feeding activities of the grubs can no longer be saved, since the above-ground parts of the plant can no longer be adequately supplied with water and nutrients due to the lack of roots. They dry up and can easily be pulled out of the ground. To prevent the infestation from spreading to other plants, you should fight the grubs as described in this section.

    collect

    In earlier times, children collected cockchafers and their larvae in the summer months - in some years there was a regular plague of cockchafers, so that the animals were radically combated. Even today, collection, albeit laborious, is a target-oriented control method. It is best to wait after a heavy downpour, because then the little animals come to the surface and can be easily collected. Alternatively, water the infested garden areas vigorously with the garden hose and thus attract the grubs upwards. Of course, you can also dig up the soil thoroughly and remove dug up larvae. However, this method is only advisable if the bed is free or is to be cleared anyway.

    Biological control with nematodes

    Easier to carry out and just as effective is the use of nematodes. These are nematodes that you can buy in specialist shops specifically against May or June beetles. The tiny animals are delivered in clay granules, which they stir into water and then pour into the bed - in the evening if possible, because nematodes die quickly when they come into contact with UV light. The microscopic nematodes only become active in the soil, penetrate the bodies of the grubs and kill them.

    With beneficial insects against grubs

    Birds love to eat grubs

    It is particularly practical to have animal helpers in the garden when fighting grubs. The thick larvae, like the beetles, are a popular food for hedgehogs, moles, birds, mice and bats, and they eat them up diligently. So if you make these beneficial insects comfortable in the garden, then the pest population will remain small from the start. These measures will help:

    • Setting up and attaching quarters: for example piles of brushwood and stones as hiding places, hedgehog and bird houses, bat boxes
    • feeding stations and drinking troughs: for birds and hedgehogs, e.g. feeding hedgehogs in autumn and feeding birds in winter (water troughs in summer)
    • Planting of protective and forage plants: for example dense hedges, native fruit trees (rowanberry, cornelian cherry, hawthorn etc.)

    If you have chickens, let them run over fallow beds, lawns and meadows in spring or autumn - the animals pick the tasty grubs out of the ground. But be careful: Chickens like to scratch and don't stop at delicious vegetables (such as salad), so don't let the cackling flock into the freshly planted or seeded garden.

    Does the use of insecticides against grubs make sense?

    Some pesticides that are effective against grubs and approved for home and hobby gardens are available in specialist shops. Products made from the seeds of the Indian neem tree are very effective. These contain toxic ingredients that hinder the development of beetle larvae and other pests or even kill them. But be careful: Just because it is a natural product does not mean that it is harmless. Neem oil also has serious effects on the garden ecosystem and also damages useful insects and other garden dwellers - for example birds or hedgehogs. You should therefore only resort to such means when all other methods have failed and you have practically no other choice.

    digression

    Which home remedies help against grubs?

    Horse dung attracts grubs

    An old home remedy for grubs is horse manure. Between April and May, dig horse manure traps in the garden soil, consisting of buckets filled with fresh manure. The opening of the bucket should be flush with the surface of the earth. The beetle larvae - at least those that haven't eaten roots yet - are attracted by the smell of manure and crawl inside. Now all you have to do is dig out the buckets and bury the manure and grubs somewhere else. If you repeat this procedure every year, you will soon no longer have a problem with beetle larvae.

    What else helps against grubs? Combat in the garden and on the balcony

    "Lots of cockchafers give hope for a good year." (Old farmer's rule)

    Now grubs not only cavort in the garden bed, but also on the compost, in the raised bed, in the flower pot or in the balcony box. You can find out here what helps against the larvae in such cases or whether targeted control is necessary or sensible at all.

    Fighting grubs in the lawn

    If larger brown spots suddenly appear in the lawn, which gradually increase in size, then grubs could be behind them. You can investigate this more closely by simply digging up a patch of the affected lawn - you'll likely find some beetle larvae there. If not, the dried up grasses most likely have another cause.

    The methods and means already described help against an infestation. You can also cover smaller lawn areas with an insect protection net during the approximately three-week flight period of the beetles. Nematodes of the Heterorhabditis and Steinernema species are also practical for use on lawns, and you can spread them over large areas from temperatures of twelve degrees Celsius.

    Fertilization with calcium cyanamide

    If you not only want to get rid of the grubs, but also weeds, moss and all kinds of other lawn problems, fertilize your lawn with calcium cyanamide - this is highly toxic to the beetle larvae and therefore kills them. However, this is only advisable if the pH of the soil is below 6.5. So before you use it, do a pH test, which can be done with a simple test stick from a hardware store or pharmacy. Then mix a heaping tablespoon of calcium cyanamide per square meter of lawn with a generous shovel of compost and distribute both as evenly as possible.

    tips

    The damage to the lawn caused by grubs can be repaired with lawn pavers, ready-made turf (e.g. rolled turf) or new seeding.

    grubs in the raised bed

    The useful rose chafer larvae should be left in the bed

    Raised beds with their rich filling and humus-rich soil are a popular playground for grubs. Here, too, it is important to carry out a test before trying to combat it - you should leave useful beetle larvae such as those of the rose chafer in the bed, after all they contribute to the formation of humus. On the other hand, you either collect May and June beetle larvae or, in the case of a very heavy infestation, fight them by simply changing the potting soil. Of course, this only works if the raised bed has not yet been planted.

    If, on the other hand, you only discover the grubs when the raised bed is already fully planted, only these measures will help:

    • Collect, if possible after watering or a downpour
    • use of nematodes
    • Horse manure trap (also works with compost)

    Be sure to plant garlic in the raised bed - for example in a mixed culture with strawberries - as May beetles and June beetles and their larvae avoid its strong smell. In spring, it also makes sense to cover the raised bed with an insect protection net as a preventive measure. This not only helps against grubs, but also against other common pests and hungry birds that are only too happy to peck at the freshly planted seed.

    grubs in the flowerpot

    If, on the other hand, grubs are found in the flower pot, only consistent repotting and complete replacement of the substrate will help. Regular repotting and protective measures such as covering with an insect protection net also help to prevent re-colonization. Incidentally, beetle eggs and larvae are sometimes found in potting or potting soil, so they are brought in.Previous disinfection of the substrate in the oven or in the microwave can kill the unwanted accessories (as well as any fungus gnat eggs or fungi that may be present).

    The disinfection takes place

    • in the oven for half an hour at 200 degrees Celsius
    • in the microwave for ten minutes at the highest level (600 or 800 watts)

    Moisten the substrate well beforehand and do not forget to open the window. With both methods, an intense, not necessarily pleasant smell develops.

    Effectively prevent grubs

    Insect protection nets prevent the females from laying eggs

    You can prevent an infestation with harmful grubs by making the garden unattractive for the adult beetles, especially during the main flight season. Do not leave lights on at dusk or at night, including solar lights along the main walkway - these only attract the beetles, causing females to lay more eggs in lighted gardens. Other proven methods of prevention include:

    • insect protection nets: During the beetles' main flight season, place insect protection nets on bed areas, manure and compost heaps. These prevent the female beetle from laying eggs.
    • groundwork: Typical gardening tasks such as hoeing, raking, weeding and digging disturb and damage the beetle larvae.
    • root protection mesh: Rootstocks that are protected in this way cannot be reached by grubs and therefore cannot be eaten.

    You should also make it difficult for the grubs to get to the feast, for example by surrounding garden beds with lawn curbs that go deep into the ground. These represent an insurmountable barrier so that the little animals cannot migrate from neighboring plants or beds.

    digression

    Which plants help against grubs?

    Certain plants also have a preventive effect against grubs. Garlic, geraniums (“geraniums” for the balcony gardener) and delphiniums in particular are very unpopular with the beetle larvae, which is why beds planted with these plants are avoided as much as possible.

    frequently asked Questions

    When do grubs hatch?

    Most scarab beetles mate between April and May, after which the females lay their eggs. Finally, in the months of June and July, white grubs hatch in the ground. They remain in the soil for between three and five years before pupating and developing into mature beetles.

    How long does the development from grub to cockchafer take?

    Cockchafers and other beetles are grubs for most of their lives

    Cockchafers and other scarab beetles spend most of their lives as grubs - their development from the larval to the mature beetle stage takes between three and five years. Adult beetles - called imago - are granted only a short lifespan: the male dies after the nuptial flight, the females after laying their eggs. The adult phase usually lasts about four to seven weeks.

    How long do grubs survive in the ground?

    Engraved grubs stay in the ground for between three and five years. The rate at which they develop depends primarily on the region and the prevailing climate there: In warmer regions, the development from larva to beetle is faster than in colder climate zones. However, by no means all grubs reach the adult stage: a large proportion are eaten by predators beforehand, succumb to infections (e.g. from fungi), are killed by gardeners or simply do not survive the winter.

    How deep are grubs in the ground?

    May and June beetle larvae are close to the surface, after all they mainly eat roots. You can usually find them at a depth of between five and 25 centimetres. Only when they pupate do the grubs migrate deeper: the pupae can now be found up to 60 centimeters deep. They stay here for about a year or two.

    Can you eat grubs?

    In this country - in contrast to other regions of the world - it is not common to eat beetle larvae and most people are likely to develop quite a disgust at the idea. In fact, grubs are edible, although we do not recommend eating them. Depending on what such a grub has eaten, it can be highly toxic and therefore harmful to health. The toxins of many plants do not bother the larvae, but they absorb them in their bodies and pass them on to their predators.

    tips

    If grubs appear in the compost, they are usually the larvae of the rose chafer. They help turn the garden waste into compost and are therefore very useful. Dig them back in quickly, as the little creatures do not tolerate the sunlight and die quickly.

Category:

Animals in the garden