The scarab beetle larvae in particular, known as grubs, are a major problem in agriculture and gardening in some years, as they often destroy large-scale plantings within a short period of time due to their often massive appearance. We have summarized for you in this article what actually helps against the different types.
How to fight scarab beetles in the garden?
Scarf beetles can cause damage to the garden through their grub larvae, which eat plant roots. Preventative measures include insect protection nets, root protection screens and regular tillage. To combat this, you can collect the beetles, use biological agents such as nematodes and encourage natural predators in your garden.
How to recognize a scarab beetle in good time
Grubs do not eat plant roots for years, but initially feed on humus. It is only from the second year onwards that the larvae feast on the fine roots (and, depending on the species, other plant remains) before burrowing up to 60 centimeters deep into the ground and pupating. They remain in this state for another one to two years. While the adult beetles can be identified quite quickly - and egg-laying is likely - the grubs are often only discovered by chance.
The plants in the affected areas die off apparently without cause. If you can rule out other reasons, the grub infestation can be confirmed quite easily by a test excavation of the affected area: the yellowish-white larvae are in the excavation. By the way, you don't have to dig particularly deep, because the animals are only a few centimeters below the surface of the earth.
While the beetles “only” cause damage above ground, the larvae quietly eat the roots
Prevention is better than fighting
You can prevent an infestation with scarab beetles and their larvae with a few targeted measures. However, these methods are not 100% safe. The most important thing is not to leave any lights on in the garden during the main flight period of the various species: the animals, which are mostly active at night or at dusk, are attracted to them and prefer to lay their eggs near light sources. Other sensible options for prevention are:
- Insect protection nets: especially on compost and manure heaps as well as on open ground
- Root protection grid: protect the rootstocks of plants from the larvae
- Lawn curbs: Surround beds with deep curbs, the grubs can't get through here
- Soil work: hoeing, raking, pulling weeds and regular digging of the ground in spring or autumn disturbs and damages the grubs
Tip
To protect lawns from dying off caused by grubs, you should scarify the turf regularly. However, if that no longer helps, you should remove the dead lawn, dig up the area deeply and reseed.
Effectively combat scarab beetles
“Collect the cockchafers and tear off their legs and wings. Then roast them in hot butter until crispy. Then cook them in chicken soup.” (Centuries-old recipe for cockchafer soup)
If the damage is already visible, the plants that have been eaten by grubs can no longer be helped. Since the larvae eat the underground roots, the above-ground parts of the plant can no longer be supplied and dry out. In addition, cockchafer larvae are appearing in large numbers - where you find one maggot, there are certainly many others in the ground. So it's no wonder that the former numerous populations were collected and processed into, for example, a nutritious cockchafer soup - perhaps your grandparents still know this.
With regard to effective control, you have the following options in the garden.
Collect
Even in earlier times, one of the main activities of children during the summer months was collecting cockchafers and their larvae. Even today, the method is effective for hobby gardens, even if it is laborious and time-consuming. The easiest way to collect the grubs is after a heavy downpour, because then the animals come to the surface and can be easily picked up. Such rain can be artificially imitated by watering the affected areas heavily.
Alternatively, simply dig up the ground riddled with grubs and bring the larvae into the light. This method also has the advantage of loosening the soil and removing weeds.
Biological control with nematodes
Nematodes (€29.00 on Amazon) are available in stores specifically to combat the larvae of May or June beetles, which reliably kill the pests. These are microscopic roundworms that are delivered in clay granules. Simply mix the granules with the irrigation water and water the affected areas in the garden thoroughly. The nematodes become active in the soil, penetrate the grubs and kill them.
Natural enemies
Birds are the best protection against scarab beetle plagues
One of the best methods to combat annoying grubs is to make the garden inviting for hedgehogs, moles, bats and birds. These love to eat the fat maggots and the adult beetles and thus keep the population low in a completely natural way. Mice, martens and large ground beetles also like to eat grubs. To make the beneficial insects feel comfortable, install
- appropriate roosts (birdhouses, bat boxes, piles of brushwood)
- Waters and feeding stations with a few treats (birds feed in winter!)
- Planting fodder and protective plants, such as dense hedges
If you are also the happy owner of a flock of chickens, you can let them run over fallow beds in spring and autumn and over meadows and lawns all year round. The animals specifically peck the grubs out of the ground.
Insecticides against scarab beetles?
Some pesticides that reliably eliminate grubs are approved for home and hobby gardens as well as for lawns. These include, for example, products made from the seeds of the neem tree native to India, whose toxic ingredients hinder the development of the larvae. However, if possible, you should not use insecticides, as these - regardless of whether they are chemical or natural agents such as neem oil - always have a serious impact on the entire ecosystem in the garden and therefore also on useful animals.
Just because a product has the label “natural” does not mean it is safe. After all, nature itself produces the most harmful poisons and is therefore anything but “gentle”.
What are scarab beetles?
The scarab beetles (lat. Scarabaeidae) are a very large and complex family within the order of beetles (lat. Coleoptera). Around 27,000 different species in around 1,600 genera belong to the family of beetles that occur worldwide. They look very different from the outside and can range in length from a tiny two millimeters to a strikingly large 16 centimeters. Not all species pose a problem in hobby gardens, some - such as the rhinoceros beetle, which is threatened with extinction and is therefore protected - are also considered to be extremely beneficial.
Species
Typical scarab beetle species relevant to the garden are primarily the following:
- June beetle: also ribbed curlew beetle, Latin Amphimallon solstitiale
- Common cockchafer: also field cockchafer, Latin Melolontha melolontha
- Golden rose beetles: also common rose beetle, Latin Cetonia aurata
- Rhinoceros Beetle: Latin Oryctes nasicornis, feeds on dead wood and is therefore often found in bark mulch
- Garden leaf beetle: Latin Phyllopertha horticola, are often confused with the June beetle, but cause little damage
For many centuries, the cockchafer in particular was decried as a pest and every year could cause considerable damage - and thus also famine - through the immense feeding activity of its grubs. Nowadays, the cockchafer has become rare due to drastic measures, mainly in the 1950s and 1960s, but still causes great damage in warm years and in certain regions. The following video shows the newly emerged problem quite clearly:
Typical appearance of scarab beetles
The scarab beetles mentioned above look very similar, so confusion cannot be ruled out. However, it is important to accurately identify the species occurring in the garden because otherwise the control measures may be ineffective - not every beetle grub responds as desired to the elimination methods introduced. For this reason, you will find some relevant clues for precise species identification in the following table:
| Cockchafer | June beetle | Gold Shiny Rose Beetle | Garden leaf beetle | Rhino Beetle | |
|---|---|---|---|---|---|
| Occurrences | almost all of Europe, rare on the Mediterranean | Northern and Central Europe outside the mountains | Europe and Asia, v. a. Central and Northern Europe | all of Europe and Asia | Europe, Asia, Africa |
| habitat | open landscapes with few trees | Fields, gardens, forest edges, parks | Hedges, gardens, forest edges, parks | in meadows, fields, on the edges of forests, in gardens and hedges | especially in forests, also in tree-lined gardens and parks, compost heaps |
| Frequency | now more common again | locally dependent, common to rare | locally dependent, common to rare | widespread | rare |
| Diet of the adult beetle | Leaves of deciduous trees | Leaves and flowers | common in flowers (pollen, nectar, sap) | Birch, hazel and oak leaves, rose and cherry blossoms | Plant juices (e.g. from tree leaves) |
| Diet of grubs | Plant roots, plant remains | Dead wood, often in bark mulch and compost | Plant roots, especially in lawns | Dead wood, often in bark mulch and compost | |
| Top wing | red-brown, can be lighter or darker | three raised longitudinal ribs, dotted in between | two wide longitudinal ribs, white transverse grooves and spots | light brown, six dotted longitudinal stripes on each wing | smooth and shiny, with fine rows of dots |
| Coloring | black except for legs, elytra and antennae | dark yellow to brown | green to bronze-colored, shiny metallic, red-gold underside | black-green, shiny metallic except for wing coverts | dark reddish brown to black, very shiny |
| Size | two to three centimeters | 14 to 18 millimeters | 14 to 20 millimeters | 8 to 11 millimeters | 2, 5 to 4 centimeters |
| Special license plates | End of abdomen not covered by wings | light midline between pronotum and elytra | different colors possible, but always shiny metallic | thick hair all over the body | Only males wear the eponymous “horn” |
| Flight time | from the beginning of May to the beginning of June | from the beginning of June | April to October | End of May to end of June | May to June |
| Larval activity | from July | from mid to end of July | from June | July to October | from June |
| Grubs Appearance | three pairs of legs, yellowish-white, brown head capsule, curved | yellowish-white, brown head capsule, curved | whitish, rather chubby, hunched posture | yellowish-white | white, cylindrical, curved posture |
| Grubs Size | seemingly ten segments | up to five centimeters | up to five centimeters | comparable to the cockchafer | larger than typical grubs, up to 12 centimeters |
| Classification | Pest | Pest | Beneficial insect | Pest | protected beneficial insect |
Lifestyle and reproduction
Scarf beetles show very different lifestyles and dietary preferences. In addition to the grubs that live on plant roots, there are species that live primarily on dead wood or collect dung. The latter group includes, for example, the various dung beetles or the species known as “pill-pushers”. Some Scarabaeidae are extremely useful in the garden - such as rose chafers or rhinoceros beetles - others cause considerable damage. Many scarab beetles are nocturnal and only become active at dusk.
Development of the larvae
The life cycles and development of the larvae also differ greatly between the individual species. The following table shows the main differences between the garden pests May beetles and June beetles:
| Cockchafer | June beetle | |
|---|---|---|
| Egg laying | May to June | June to July |
| Larval hatching | End of June | End of July |
| Pupation | July / August | August / September |
| Duration of the larval stage | 3 to 5 years | 2 to 3 years |
| Hatching of adult beetles | April to May | May to June |
Larva, pupa and beetle – All beetles go through these steps
Also characteristic of many scarab beetle species is the fact that the larvae sometimes remain in the ground for years. The grubs only pupate after two to five years and then emerge as adult beetles in the spring. However, the adult animals called imago do not live for very long: May and June beetles usually do not live longer than four to six weeks and usually only lay eggs once. For this reason, infestations often only occur every several years - cockchafers, for example, plague gardeners about every four years.
Background
May beetle or June beetle?
The larvae of the various scarab beetles look very similar to one another. However, you can distinguish them from each other based on the time period in which they appeared, the locations where they were found and the way in which they moved. When turned on their backs, the grubs of the following varieties crawl away as described:
- Cockchafer: sideways, meandering
- June beetle: crawling on its stomach
- Rose beetle: on the back, caterpillar-like
The larvae of the rhinoceros beetle, on the other hand, can be easily recognized by their size.
Frequently asked questions
What to do if scarab beetles get lost in the apartment?
If a May or June beetle gets into your apartment, simply catch it and release it back into the open through a window. The animals will most likely mistake you or your furniture for a tree and quickly land on it. Scarab beetles are neither dangerous nor poisonous to humans.
How long do scarab beetles live?
While the beetle larvae - depending on the species - remain in the soil for up to four years, adult scarab beetles are usually not granted a long life. May and June beetles, for example, fly for four to a maximum of six weeks and then die immediately after laying their eggs.
Can scarab beetles bite?
If you have a May or June beetle sitting on your arm and annoying it, it can bite you quite painfully. However, this only happens very rarely and is completely harmless.
Tip
Plant garlic as well as delphiniums and geraniums (i.e. the pelargoniums better known as balcony flowers) between your beds and prevent grub infestation. The animals don't like these plants and try to avoid them.