Garden beetles, which to worry about and which to leave

March 3, 2025

You find chewed leaves and half eaten flowers, you find a beetle sitting on the plant, and it is very tempting to join those two facts together and go and get something to spray. Plenty of the time the beetle you caught is either innocent or is the one eating whatever made the hole, so the identification is worth doing first, and it takes a few minutes rather than a season.

I get corrected on this stuff regularly by people who have been gardening a lot longer than I have, and it has never once been a bad thing, so if you know a beetle I have got wrong here I would genuinely like to hear about it in the shop.

The ones that actually cost you something here

African black beetle. A shiny black beetle around 12mm long that lives in the soil. The adults chew through seedling stems right at ground level, so plants fall over looking like something has cut them, and the larvae are the curl grubs that wreck a lawn from underneath.
Curl grubs. Fat, white, C shaped things with an orange head that you turn up in the soil or under lawn. If a patch of lawn goes spongy and you can lift it like carpet because the roots have gone, that is what has been at it.
Vegetable weevil and garden weevil. Dull grey brown weevils that feed at night and hide in the mulch during the day, chewing notches out of the edges of leaves on carrots, brassicas and a long list of other things.
The 28 spotted potato ladybird. The one that catches everybody, and it is covered on its own below.
Eucalyptus leaf beetles. These only matter if you have gums, and a big tree will wear a season of them without much trouble.

The beetle that looks like a friend and is not

Most people know to leave ladybirds alone, which is exactly why the 28 spotted potato ladybird gets away with it. It is a genuine ladybird and it is a leaf eater, and it works over potato, tomato, zucchini, pumpkin and bean leaves until they look like lace, with the veins left behind and the green scraped out between them.

Two things tell it apart from the helpful ones. Count the spots, because the predatory ladybirds in a home garden carry a handful and this one carries somewhere around 26 to 28. Then look at the shine, because the helpful ones are glossy and this one is dull and finely furry, so it looks slightly dusty in the light. The damage pattern gives it away as well, since no predatory ladybird has ever eaten a leaf.

The ones to leave exactly where they are

Ladybirds and their larvae. The larvae look nothing like the adults, more like tiny black and orange alligators, and they eat more aphids than the adults do. They get squashed by mistake constantly.
Ground beetles. Big, fast, black beetles that run for cover when you lift a pot. They hunt at night and they take slugs, snail eggs and caterpillars while you are asleep.
Rove beetles. Long and narrow with very short wing covers, so they look a bit like an earwig without the pincers. Also predators.
Soldier beetles. The orange and black ones that turn up in numbers on flowers in early summer. The adults are mostly there for pollen and nectar and the larvae are the predatory stage, down in the litter.

What to do about the ones that are a problem

Start with the free things. Go out after dark with a torch, because most of the weevils and beetles doing the damage feed at night and you will see in 10 minutes what you have been guessing about for a fortnight. Pick them into a bucket. Pull mulch back a hand span from the base of seedlings for a few weeks, since that is where the weevils shelter during the day, and put the mulch back once the plants are big enough not to care.

For curl grubs in lawn, a healthy lawn tolerates a surprising number of them, so it is worth digging a 300mm square out and counting before you treat anything. A handful in that square is normal. Thirty of them is a problem, and that is when a hose on treatment or a granule is worth using, watered in properly so it gets down to where the grubs are rather than sitting on the leaf.

Keep any spray narrow and put it only on the plant with the problem. A broad knockdown over the whole patch takes the ground beetles and the ladybirds with it, and then there is nothing left hunting for you and you are on your own next time.

Build the garden so the predators stay

Ground beetles and rove beetles want somewhere damp and dark to spend the day, so a mulched bed, a bit of leaf litter left in a corner and a couple of flat rocks or a piece of old timber left on the soil will hold them. Flowers keep the adult stages fed, and the small open flowers work better than the big showy ones because short mouthparts can reach the nectar.

Give it a full season before you judge it. The predators cannot turn up until there is something for them to eat and somewhere for them to live, which means the patch usually gets slightly worse before it gets better.

Shop related products

Lawn Grub & Beetle Kill Hose On 2L. Hose on treatment for curl grubs and lawn beetles.
Contender Insecticide RTU 750ml. Ready to use, for spot treating one plant rather than the patch.
Multicrop Pyrethrum Long Life Insect Spray 1L. Fast knockdown, and broad, so keep it for last.
D.T. Brown Alyssum, 750 seed pack. Small open flowers that feed the adult predators.
D.T. Brown Australian Native Flower Mix, 500 seed pack. Nectar through the warmer months.

Did you know we also stock grub granules in a 500g pack and a 2.5kg lawn grub and insect control, neither of which is on the website, so give us a ring on (08) 8536 4333 to check what is on the shelf.

The sprays and the seed are in the garden centre, and the pest control range is the part you want for this.