Q: Can you tell me what this insect is? It’s feasting on my dahlia leaves. I don’t use insecticides in the garden so can handpick and squash them if I have to. If they’re not going to do too much harm I’m happy to leave them alone. DK, Co Waterford
A: You’ll be delighted to know that there’s no need at all to spray, squash or handpick this colourful little fellow, which is a very beneficial garden insect known as the red soldier beetle that does a lot of great work on behalf of us gardeners. It’s not responsible for the damage to your dahlias but instead was probably there to hoover up any spider mites, aphids or honeydew on the plants or to feast on the flowers’ pollen and nectar. Its love of pollen and nectar means that it also plays a useful role as a pollinator, yet another reason to value its presence in the garden.
The adult beetles emerge in high summer and are most active on warm, sunny days. They’re well known for their ostentatiously amorous displays as well as their particular fondness for umbelliferous-type flowers such as cow parsley and hogweed, which has earned them the nickname of the hogweed bonking beetle.
After mating, the female beetle then lays her eggs in the soil, which hatch out into small, dark, ground-dwelling caterpillar-like larvae. These larvae also play a beneficial role in the garden by preying on slugs and snails.
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As for the damage to your dahlias, this is probably being caused by slugs and snails, which love to feast on the leaves and flower buds of these showy, frost-tender tuberous plants. Earwigs and the caterpillars of some species can also nibble on the foliage. A little damage won’t cause any serious harm but if it becomes widespread, then I’d suggest hand-picking any slugs, snails or caterpillars that you find close on or close to the base of the plants and then either depositing them in your compost heap or squashing them.
Good garden hygiene and the occasional use of organically acceptable slug pellets will also help to minimise damage. So will simple home-made earwig traps, using upturned small plant pots filled with damp, torn-up leaves or hay. Check these regularly and then carefully dispose of the earwigs off-site or by dropping them into a bucket of soapy water. Dahlia plants also hugely appreciate regular liquid seaweed foliar feeds from now until the first harsh frosts to keep them healthy and happy.
