Blue Mint Beetle
Blue Mint Beetle
Chrysolina coerulans is a small, metallic blue leaf beetle. They favour plants in the Mentha genus but have been recorded on other herbaceous plants, too. The Blue Mint Beetle may be a pest of Mint in gardens. Both the adult beetles and larvae will graze on the plant leaves, leaving behind small holes. Blue Mint Beetles are common in gardens containing any plant in the Mint family (Lamiaceae). They favour wet or damp habitats, such as river margins and woodland. Most healthy, well-established plants can withstand the damage done by the Blue Mint Beetle. If plants begin to look less vigorous, beetles can be removed by hand.
Beetles are food for other wildlife.
Adult beetles and larvae eat the leaves of mint.
Adults: Adult beetles are quite small in size, measuring around 0.7- 1.0 cm. Colour is a dark, metallic blue. They have a rounded, circular shape. Larvae: Larvae are soft-bodied and shiny, rounded in shape and grey-black. Tip* These beetles are not to be confused with the Green Mint Beetle, that is native to the UK. The latter are metallic emerald and lengthier (8-9mm) than the Blue Mint, but this isn't always the case. The Blue Mint Beetle is more round, too.
Holes in mint leaves. Metallic blue beetles hiding beneath leaves. Small, black, grub-like, larvae under leaves.
Mint plants can tolerate some damage. However, beetles can be removed by hand if infestations become too heavy.
It's not advised to chemically treat plants that are intended to be used for culinary purposes. Likewise, pesticides should be avoided if near water bodies. It's best to try and target the larvae as these are more susceptible to chemicals. There is a range of organic pesticides on the market, such as pyrethrums. Please read and follow the manufacturer's instructions before any products are used. More persistent chemicals typically have a non-selective mode of action, meaning anything the chemical comes in contact with, will be affected.