The five-spot burnet moth (Zygaena trifolii) is a distinctive day-flying moth of unimproved grassland and coastal habitats. Its vivid red-and-black wing pattern serves as aposematic coloration — warning potential predators of its toxicity from cyanogenic compounds sequestered from larval food plants. Like many specialist grassland invertebrates, it has declined substantially with the loss of unimproved meadows and calcareous grassland.
Identification and Biology
Adults fly from June to August. The forewings are black-green with five crimson spots (the name-giving feature). Both adults and larvae contain hydrogen cyanide (HCN) sequestered from bird's-foot trefoil (Lotus corniculatus) and other trefoil species — making them toxic to most predators. Their conspicuous wing pattern advertises this toxicity, providing effective protection despite flying slowly in daylight.
Habitat Requirements
Five-spot burnets require short-turfed, flower-rich grassland with abundant trefoils for larval feeding. Key habitats include:
- Unimproved neutral and calcareous grassland managed by grazing or hay cutting
- Coastal cliff tops and dune slacks
- Traditional hay meadows with diverse wildflower communities
- Restored grassland and road verges managed sensitively
Life Cycle
Eggs are laid in batches on trefoil leaves. Larvae hatch and feed through late summer, overwintering as partially grown caterpillars and resuming feeding the following spring. Pupation occurs in papery cocoons attached to grass stems in May–June. The bivoltine or univoltine nature of populations depends on latitude and local climate conditions.
Conservation Challenges
- Loss of unimproved grassland — the primary driver of decline; 97% of UK lowland meadow lost since the 1930s
- Agricultural intensification removing trefoils through fertiliser use and reseeding
- Inappropriate grassland management — too-early cutting destroys pupae; cessation of cutting allows scrub encroachment
- Road verge management — verges are important linear habitats; early cutting before moth flight season reduces adult populations
Conservation Actions
Agri-environment schemes supporting late hay cutting, low fertiliser inputs, and diverse sward composition benefit five-spot burnets and the wider community of grassland invertebrates. Road verge management guidelines increasingly recommend avoiding cutting during June–August to protect flying invertebrates. Wildflower meadow creation and restoration on appropriate soils provides new habitat in fragmented landscapes.