Grubs - they look like fat, white caterpillars - live in almost every garden. These are the larvae of various species of beetles, some harmful and others very useful. In this article you will find out how to distinguish between pests and beneficial insects and how to combat the former effectively.
What are grubs?
Grubs are the larvae of various species of beetles. Some grubs are used to produce humus. Others are pests. Their food is decomposed plant material and plant roots. Grubs can cause drastic damage, especially to young plants. They can be distinguished by distinctive features.
- The larvae of the various scarab beetle species are called grubs.
- Most grubs live in the ground for years, but are also found in raised beds, flower pots or compost.
- Not all grubs are pests, some - such as the larvae of the rose beetle or the rhinoceros beetle - are even very useful for humus production and are therefore welcome guests in the compost heap.
- Harmful grubs can be controlled using various non-toxic methods, but they usually only become a problem when they appear in large numbers.
What are grubs?
Grubs are relatively large, mostly bright larvae
Grubs are the larvae of various species of beetles from the scarab beetle family (Latin: Scarabaeidae). The name comes from Old or Middle High German and refers to the appearance of the larvae: It means something like “maggot” or “small worm”.
Scarf beetles are a very large family that includes 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 cockchafer, whose grubs could cause considerable damage and cause famine in earlier centuries. In the 1950s and 1960s the animals were radically combated, so that they can hardly be found today. In some years they still occur massively and can cause major regional damage.
However, not all scarab beetles and their associated grubs can be classified as pests. Quite the opposite, because the larvae of the rose beetle and the very rare rhinoceros beetle (which is also a protected species) are considered extremely beneficial insects.
In the garden and on the balcony you will mainly find these species:
| Cockchafer | June beetle | Garden leaf beetle | rose beetle | Rhino Beetle | |
|---|---|---|---|---|---|
| Latin name | Melolontha melolontha | Amphimallon solstitiale | Phyllopertha horticola | Cetonia aurata | Oryctes nasicornis |
| Alternative names | Field Cockchafer | Ribbed Curlew Beetle | – | Golden rose beetle, common rose beetle | – |
| Frequency | Almost extinct, now more common again | common to rare depending on region | very common, widespread | common to rare depending on region | rare, is protected |
| Flight time | Early May to early June | from the beginning of June | between the end of May and the end of 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 millimeters |
| Coloring | black except for legs, antennae and elytra | dark yellow to brown | black-green except for elytra, shiny metallic | shiny metallic, green to bronze, red-gold underside | very shiny, dark brown to black |
| Top wing | red-brown | three longitudinal ribs, dotted between them | six longitudinal stripes on each wing, light brown | white transverse grooves and spots, two wide longitudinal ribs | shiny and smooth, fine dotted rows |
| Special features | Wings do not cover the end of the abdomen | between elytra and pronotum bright midline | thick hair | always shiny metallic, different colors possible | eponymous horn (only for males) |
The beetles are active at dusk, which is why you will find them either in the evening or early in the morning.
What do grubs eat?
While the adult beetles usually feed on leaves, flowers or plant juices, their grubs live in the soil and prefer to eat decomposing plant material and living plant roots. The larvae of the May, June and garden leaf beetles like to attack plant roots and can damage the vegetation in the garden. The rose or rhinoceros beetle grubs, on the other hand, mainly eat dead wood and other dead plant material. That's why rose beetle grubs in particular are often found in compost. There they help convert the plant residues into valuable compost.
Harmful grubs or beneficial insects?
There are grubs in every garden. The pest larvae of the May beetle, for example, usually cause little damage, at least if they only occur sporadically. They only become a problem when they occur on a massive scale. It also makes sense not to kill all the thick, white maggots straight away: you should be able to distinguish those of the rose beetle and rhinoceros beetle from the harmful species. They are very useful and should therefore be left alive. But you can also let the larvae of May beetles etc. live so that these rare animals are not brought back to the brink of extinction - at least if you only find individual grubs.
Identifying grubs: Characteristic differences
| Cockchafer | June beetle | Garden leaf beetle | rose beetle | Rhino Beetle | |
|---|---|---|---|---|---|
| Classification | Pest | Pest | Pest | Beneficial insect | Beneficial insect |
| Larval activity | from the end of June | from mid to end of July | July to October | from June | from June |
| Size | up to five centimeters | up to five centimeters | significantly smaller than May or June beetles | up to five centimeters | up to 12 centimeters |
| Coloring | yellowish-white with brown head capsule | yellowish-white with brown head capsule | yellowish-white | whitish | whitish |
| Appearance | curved, three pairs of legs | curved, three pairs of legs | curved, three pairs of legs | fat, curved, three pairs of legs | cylindrical, curved, three pairs of legs |
| Special features | pronounced abdomen, divided into two by annular groove | no division of the abdomen | no division of the abdomen | often in compost or rotten wood | significantly larger than other grubs |
You can also distinguish between harmful and useful grubs using this test:
- Turn the grub on its back.
- Larvae of the May or June beetle remain lying down
- or try to move sideways.
- June beetle larvae usually crawl while lying on their stomachs.
- Rose beetle larvae stretch all pairs of legs backwards into the air
- and move with caterpillar-like movements.
The larvae of the rhinoceros beetle, however, are easily distinguishable from the other grubs by their sheer size.
Identifying grubs: lifestyle and damage pattern
But what characteristics can you tell that there is a problem with grubs in the garden? We will now address this question in this section.
Lifestyle and harmful image
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 May beetles and curlew beetles do not feed exclusively on plant roots - these varieties also eat plant residues and live in humus. Only after pupation do the now adult beetles leave the earth and can mainly be seen at dusk.
While the rather large beetles are noticeable in the garden, an infestation with grubs is usually noticed late or by accident - for example when digging up a bed. Attention is required when plants seem to be threatening to die for no reason - they can often simply be pulled out of the ground due to missing roots. If you then dig a little into the earth, you will find thick, white grubs.
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These plants are particularly endangered
Basically almost all plant species can be attacked, grubs are not particularly picky in this regard. However, they particularly like to nibble on the roots of young plants (especially vegetables, lettuce and strawberries), potatoes and beets. Grass roots, on the other hand, are the favorite food of the larvae of the garden leaf beetle (curlew beetle), which literally eat entire lawns bare when there is a heavy infestation. Typically, the blades of grass dry out and are easy to pull out of the soil - after all, the roots are missing.
Fighting grubs
Maikäfer: Invasion der Engerlinge | Unser Land | BR Fernsehen
Plants that are already visibly damaged by the grubs' feeding activity can no longer be saved, as the above-ground parts of the plant can no longer be adequately supplied with water and nutrients due to the missing roots. They dry out and can be easily pulled out of the soil. To prevent the infestation from spreading to other plants, you should combat 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 the animals were radically combated. Even today, collecting them, albeit laborious, is an effective method of combating them. It's best to wait after a heavy downpour, because then the animals come to the surface and can easily be collected. Alternatively, water the infested garden areas vigorously with the garden hose and attract the grubs upwards. Of course, you can also dig up the soil thoroughly and remove any larvae that have been dug up. However, this method is only advisable if the bed is free or needs to be cleared anyway.
Biological control with nematodes
Easier to carry out and just as effective is the use of nematodes. These are threadworms that you can buy from specialist retailers specifically to combat May or June beetles. The tiny animals are delivered in clay granules, which they stir into water and then pour into the bed - if possible in the evening, because nematodes die quickly on contact with UV light. The microscopically small 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 bring animal helpers into the garden when fighting grubs. The fat larvae as well as the beetles are a popular food for hedgehogs, moles, birds, mice and bats and are diligently eaten. 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 installing roosts: for example piles of brushwood and stones as hiding places, hedgehog and bird houses, bat boxes
- Feeding stations and waterers: for birds and hedgehogs, for example hedgehog feeding in autumn and bird feeding in winter (drinking in summer)
- Planting 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 peck the tasty grubs out of the ground. But be careful: chickens love to scratch and won't stop at delicious vegetables (such as lettuce), so don't necessarily let the cackling flock into the freshly planted or sown 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 from specialist retailers. 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 remedy does not mean it is harmless. Neem oil also has serious effects on the garden ecosystem and also harms beneficial insects and other garden inhabitants - such as birds or hedgehogs. Therefore, you should only resort to such means when all other methods have failed and you have practically no other choice left.
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Which home remedies help against grubs?
Horse manure attracts grubs
An old home remedy for grubs is horse manure. Between April and May, dig horse manure traps into the garden soil that consist of buckets filled with fresh manure. The bucket opening should be flush with the surface of the earth. The beetle larvae - at least the ones that are not yet eating roots - are attracted by the smell of manure and crawl in. Now all you have to do is dig up 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? Fighting in the garden and on the balcony
“Many cockchafers give hope for a good year.” (Old farmer’s rule)
Now grubs are not only found in the garden bed, but also in 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 or whether targeted control is even necessary or useful.
Fighting grubs in the lawn
If large brown spots suddenly appear in the lawn and gradually enlarge, then grubs could be behind them. You can investigate this suspicion further by simply digging up a section of the affected lawn - you will probably find some beetle larvae there. If not, the dried grass most likely has another cause.
The methods and remedies already described help against an infestation; you can also cover smaller lawns with an insect protection net during the beetles' flight period, which lasts about three weeks. Nematodes of the Heterorhabditis and Steinernema species are also practical for use on lawns and can be spread over large areas at temperatures of twelve degrees Celsius.
Fertilization with lime nitrogen
If you want to get rid of not only the grubs, but also weeds, moss and all sorts of other lawn problems, fertilize your lawn with lime nitrogen - this is highly toxic to the beetle larvae and therefore kills them. However, this is only advisable if the soil pH is below 6.5. So before use, do a pH test, which can be carried out with a simple test stick from the hardware store or pharmacy. Then mix a heaping tablespoon of lime nitrogen per square meter of lawn with a generous shovel of compost and distribute both as evenly as possible.
Tip
The damage to the lawn caused by grubs can be repaired by paving lawns, finished turf (e.g. rolled turf) or reseeding.
Grubs in raised beds
The useful rose beetle 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 possible control - you should leave useful beetle larvae such as those of the rose beetle in the bed, after all, they contribute to the formation of humus. On the other hand, you can either collect May and June beetle larvae or, if the infestation is very severe, fight them by simply replacing the potting soil. Of course, this only works if the raised bed has not yet been planted.
If, however, 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 mixed culture with strawberries - as May 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 sown seeds.
Grubs in a flower pot
If, on the other hand, grubs are found in the flower pot, the only thing that helps is consistent unpotting and complete replacement of the substrate. Regular repotting and protective measures such as covering it with an insect protection net also help against re-infestation. By the way, beetle eggs and larvae are sometimes found in planting or potting soil and are therefore introduced. Disinfecting the substrate beforehand in the oven or microwave can kill the unwanted accessory (as well as any fungus gnat eggs or fungi that may be present).
Disinfection takes place
- inoven for half an hour at 200 degrees Celsius
- in themicrowave for ten minutes on the highest setting (600 or 800 watts)
Wet the substrate well beforehand and don't forget to open the window. Both methods produce an intense, not necessarily pleasant smell.
Effectively prevent grubs
Insect protection nets prevent 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 any lights on at dusk or at night, including solar lights along the main path - these only attract the beetles, so that the females increasingly lay their eggs in illuminated gardens. Other proven methods for prevention include:
- Insect protection nets: Apply insect protection nets to bed areas, manure and compost heaps during the beetle's main flight season. These prevent the female beetles from laying eggs.
- Soil work: Typical gardening tasks such as hoeing, raking, weeding and digging disturb and damage the beetle larvae.
- Root protection grid: Rootstocks 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 animals cannot migrate from neighboring plants or beds.
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Which plants help against grubs?
Certain plants also have a preventive effect against grubs. Garlic, pelargoniums (“geraniums” for balcony gardeners) and delphiniums in particular are very unpopular with beetle larvae, which is why beds planted with these plants should be avoided as much as possible.
Frequently asked questions
When do grubs hatch?
The nuptial flight of most scarab beetles takes place between April and May, after which the females lay their eggs. White grubs finally hatch in the ground in the months of June and July. They stay in the ground for between three and five years before they pupate and develop into full-fledged beetles.
How long does it take to develop from a grub to a cockchafer?
May beetles and other beetles are grubs for most of their lives
Cockchafers and other scarab beetles spend the longest period 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 only granted a short lifespan: the male dies after the nuptial flight, the female after laying her eggs. The adult phase usually lasts around four to seven weeks.
How long do grubs survive in the ground?
Grubs remain in the ground for between three and five years. Their speed of development depends primarily on the region and the climate prevailing there: In warmer areas, development from larvae to beetle is faster than in colder climates. However, not all grubs reach the adult stage: a large proportion are eaten by predators, 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 found close to the surface; after all, they mainly eat roots. You can usually find them at a depth of between five and 25 centimeters. 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 one to two years.
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 probably quite disgusted by the idea. In fact, grubs are edible, even if we do not recommend their consumption. Depending on what such a grub has eaten, it can be highly poisonous and therefore harmful to he alth. The toxins of many plants do not harm the larvae, but they absorb them into their bodies and pass them on to their predators.
Tip
If grubs appear in the compost, they are usually rose beetle larvae. They help process the garden waste into compost and are therefore very useful. Dig them back in quickly as the animals cannot tolerate sunlight and will die quickly.
