Nature on our doorsteps: Useful defence mechanism for day-flying moths

Rosaleen Dwyer is the County Heritage Officer at South Dublin County Council – every week she gives us an insight into nature on our doorsteps and the beautiful biodiversity of its plants and wildlife.

While moths are generally night-time fliers, there are a few that can be spotted flitting about during the day.

Two species that are busy now in flowering meadows and grassy places are the 6-spot Burnet Moth and the Cinnabar Moth.

Both species are coloured red and black, with different combinations of spots or stripes on their wings.

The 6-spot Burnet moth is named for the 6 red spots on each of its forewings.

These front wings are beautifully iridescent, with a metallic green sheen.

Its underwings are bright red with a narrow black line around the outside.

It also has lovely long, black, club-shaped antennae, and has glossy black hairs on its body.

The Cinnabar Moth is also red and black, and at a casual glance it could be mistaken for a 6-spot Burnet.

The 6-spot Burnet Moth has 6 red spots on its metallic-green forewings

A closer look, however, reveals a red stripe or bar along the outside edge of each black forewing, with only two red spots on the bottom edge of each wing.

Like the 6-spot Burnet, the Cinnabar’s hind wing is also red with a narrow black border.

For both moth species, flying about during the day exposes them to many more predators than moths that only fly at night.

These day-fliers have therefore evolved a similar defence strategy to protect themselves.

Their caterpillars eat leaves that contain chemical compounds that either taste unpleasant or are toxic to others.

The 6-spot Burnet caterpillars feed on the leaves of Bird’s-foot trefoil, from which they absorb compounds that are related to cyanide.

Cinnabar caterpillars feed on Ragwort plants, which contain compounds that result in the accumulation of toxic levels of copper in livers.

These chemicals cause the caterpillars and the adults of both moth species to taste very unpleasant.

As a result, if a bird tries to eat one it will never try a second one, and it warns it to stay away from anything coloured black and red.