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When we dig in the garden, grubs occasionally appear. The worm-like animals are larvae of various scarab beetle species. Although the feeling of disgust is sometimes great, we do not automatically have to be concerned about our plants. First we should identify the grubs. Larvae of some species are actually plant pests and should be combated promptly. Others, on the other hand, perform extremely useful services in the earth. Let's take a close look at them.

Garden Leaf Beetle - Phyllopertha horticola

AfroBrazilian, Phyllopertha horticola 06, crop from Plantopedia, CC BY-SA 4.0

The larvae of this species of scarab beetle prefer sunny and dry lawns, especially those with a sandy subsoil. Therefore, with such a site, it is obvious to first investigate whether the larvae of the garden beetle are involved. But not every grub that is discovered under a turf must come from the garden beetle. It could also be larvae of other species, such as June beetles or May beetles. Therefore, match the external characteristics, especially the length. The larva of the garden beetle is smaller than other larvae.

  • hunched posture
  • white to yellowish body colour
  • dark head
  • three pairs of breastbones
  • Underside of rump has double row of thorns
  • When freshly hatched, the larva is about 1 mm in size
  • fully grown larva is max. 1.5 cm long
  • is found in the soil 10 to 15 cm deep

Notice: The trivial name June beetle was given to the ribbed fallow beetle described below. Occasionally, however, the garden beetle is also referred to as a June beetle because June is its month. The larvae can of course be present in the garden all year round, although not visible.

Ribbed Curlew Beetle - Amphimallon solstitiale

Bernard Ladenthin, 2022-10-13 Amphimallon solstitiale grub 2, crop from Plantopedia, CC BY 4.0

This species of beetle is widely known as the June beetle because the insects are mainly visible in the garden during this month. However, its larvae act in the soil and mainly feed on healthy grass roots. They are therefore classified as pests. They have a lifespan of about two to three years before they pupate. The grubs of the June beetle are similar in appearance to those of the may and garden chafer, which is why it is important to pay close attention to the fine differences when identifying them. The clearest identifier, however, is their mode of locomotion. So don't just look at looks.

  • cream colored body, darker head
  • evenly thick from head to tail
  • about 3 to 5 cm long
  • hunched posture (like a C)
  • Locomotion by crawling in prone position

Shiny gold rose chafer - Cetonia aurata

Fritz Geller-Grimm, Scara fg03, crop from Plantopedia, CC BY-SA 3.0

The rose beetles (Cetoniinae) are a subfamily of the scarab beetles and are represented by several species in Europe. These include the copper rose chafer, the large rose chafer and the black rose chafer. But the best known and most widespread in Germany is the shiny gold rose beetle. The beetle, which is protected by the Federal Species Protection Ordinance, is also known as the common rose beetle.

Due to their colouration, these shiny green-metallic insects are hardly to be confused with other species from the scarab beetle family. However, this does not apply to its larvae. At first glance, they too are reminiscent of fat worms. Only at second glance can they be determined more precisely. Their whereabouts can give us the first clue. They are mainly found in mulch or decomposing wood. They are also often found in garden compost. Since they feed on organic waste and convert it into humus, the larvae of Cetonia aurata are considered beneficial. The grub can be determined based on these characteristics:

  • the body has the basic color white
  • on it are gray-black shades
  • the front part of the body is slimmer
  • the head is colored brown
  • has tiny stubby legs
  • no joint kink is visible
  • at rest, the body is curved in a c-shape
  • move lying on your back
  • like a worm, with pulsating movements

Tip: If you find rose beetle larvae when turning the compost pile, you should first collect them in a box with soil. When the work is done, they are returned to the compost heap to continue their useful work there.

Cockchafer - Melolontha

Botaurus, Melolontha-melolontha-20-VII-2007, clipping from Plantopedia, CC0 1.0

Not only the cockchafer itself, but also its larvae are major pests in the garden. They only eat healthy roots, allowing plants to die. This grub will not get lost in the compost heap. But if you spot a larva near live plants, it could have hatched from a cockchafer's egg. However, as a result of extensive control measures, the population of this beetle species has since declined sharply. Friends of nature therefore leave his grubs alive, release them somewhere where their work can be accepted. How to determine the grubs:

  • their coloring is creamy white to yellowish
  • the c-shaped body is 3 to 7 cm long
  • evenly thick body shape
  • the head capsule is brown
  • Biting tools are clearly visible
  • in the chest area there are three strong pairs of legs
  • clearly developed joint creases
  • move on their side and meander

Notice: These grubs live between two and five years. We can find them in different lengths in the garden within this period of time. When they are young and short, they can easily be mistaken for June beetle larvae.

Rhinoceros Beetle - Oryctes nasicornis

Andreas Eichler, 2012.07.04.-11-Eilenburg Rhinoceros Beetle larva, section from Plantopedia, CC BY-SA 3.0

If you've spotted grubs in dead wood, compost heaps or bark mulch, they could be the larvae of the rhinoceros beetle, that pretty beetle with a horn on its head. They live on dead plant matter, especially fibrous woody debris. Since they digest organic matter which is indigestible for many microorganisms, their presence in the garden is to be welcomed. However, so that you can safely leave them where they are, you must first clearly identify the grubs based on the following characteristics:

  • brown head
  • white-yellow body
  • hunched posture
  • up to 10 cm long
  • about finger thick, regular body shape
  • has small brown dots from head to rump
  • moves stretched and on the back

Notice: The original forest dwellers are among the endangered species. The Federal Nature Conservation Act therefore prohibits removing, disturbing or destroying both beetles and larvae from nature. The sale and purchase of these beneficial insects is also prohibited by law.

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