05 October 2024

Growing Wild: Common Knapweed and Parasitoid Wasps

Catherine Keena, Teagasc Countryside Management Specialist, takes a closer look at some of our native Irish biodiversity, this time focusing on Common Knapweed and Parasitoid Wasps.

Common Knapweed

Common knapweed, one of our later flowering plants with occasional flowerheads still visible. Each deep reddish-purple compact flower with a swollen base of blackish bracts is solitary or in branched clusters. It resembles a thistle without any prickles. Grey-green simple lanceolate leaves grow alternatively up a stiff stem. Earlier it was an important source of nectar for butterflies such as peacock and meadow brown. Many flowerheads have now turned into black seedheads which remain on their hard branched stems and last throughout the winter, It can grows to a height of one metre. Common knapweed nó mínscoth i nGaeilge is part of our native Irish biodiversity.

Parasitoid Wasps

Look out for parasitoid wasps who lay their eggs inside other insects, which sooner or later causes the death of these hosts. When the eggs hatch, the larvae have a readily available source of food. They play a vital role in in the food web. In Ireland, there are over 120 ‘stinging’ wasps, which are closely related to both bees and ants. This includes our familiar black and yellow social wasps, as well as other solitary species, such as predatory digger wasps, which hunt other insects, including aphids, froghoppers, thrips and various flies. They nest in empty plant stems, dead wood, bare sand and clay banks.

Read more from the Growing Wild series