Cinnabar moth

Cinnabar moth
Both at Piddington Wood, Oxfordshire
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Lepidoptera
Family:	Erebidae
Genus:	Tyria
Species:	T. jacobaeae
Binomial name
Tyria jacobaeae (Linnaeus, 1758)
Synonyms
Phalaena jacobaeae Linnaeus, 1758 Noctua jacobaeae Linnaeus, 1758 Hippocrita jacobaeae f. confluens Schultz, 1908 Callimorpha senecionis Godart, 1822 Euchelia jacobaea ab. flavescens Thierry-Mieg, 1889

The cinnabar moth (Tyria jacobaeae) is a brightly coloured arctiid moth, found in Europe and western and central Asia. It has been introduced into New Zealand, Australia and North America to control poisonous ragwort, on which its larvae feed. The moth is named after the red mineral cinnabar because of the red patches on its predominantly black wings. Cinnabar moths are about 20mm long and have a wingspan of 32–42 mm (1.3–1.7 in).

Cinnabar moths can be found throughout Britain, except northern Scotland, wherever its larval foodplant, ragwort and groundsel, are present.

This species is so named due to the colour of the hindwings and the markings on the forewings which make it unmistakable. There is little variation although on rare occasions the pinkish markings are replaced with yellow, or the forewing is red with a black border or the wings are completely black. Easily disturbed by day and flies in sunshine. Also flies after dark. Cinnabar moths are day-flying insects. Like many other brightly coloured moths, it is unpalatable; the larvae use members of the genus Senecio as foodplants. Many members of the genus have been recorded as foodplants, but for long-term population success, the presence of the larger species such as ragwort is needed. Smaller plant species, such as groundsel, are sometimes used, but since the species lays its eggs in large batches, survival tends to be reduced. Newly hatched larvae feed from the underneath of ragwort leaves within the area of their old eggs. The larvae absorb toxic and bitter tasting alkaloid substances from the foodplants, and assimilate them, becoming unpalatable themselves.^[1] The bright colours of both the larvae and the moths act as warning signs, so they are seldom eaten by predators. An exception is among different species of Cuckoo which eat hairy and poisonous caterpillars including cinnabar moth larvae.^[2]

Females can lay up to 300 eggs, usually in batches of 30 or 60 on the underside of ragwort leaves. When the caterpillars (larvae) hatch they feed on and around the area of the hatched eggs but as they get bigger and moult (instars) they mainly feed on the leaves and flowers of the plant, and can be seen out in the open during the day.

Like several other Arctiidae moth larvae, the cinnabar caterpillars can turn cannibalistic. This can be due to lack of food, but they can eat other cinnabar larvae for no apparent reason. Females lay up to 300 eggs, usually in clusters of 30 to 60. Initially, the larvae are pale yellow, but later larval stages develop the jet black and orange/yellow striped colouring. They can grow up to 30mm, and are voracious eaters; large populations can strip entire patches of ragwort clean, a result of their low predation.

Often, very few survive to the pupal stage, mainly due to them completely consuming the food source before reaching maturity; this could be a possible explanation for their tendency to engage in seemingly random cannibalistic behaviour, as many will die from starvation. Additionally, the larvae are predated by species like the ants Formica polyctena.^[3]

The moth has proven to be particularly successful as a biocontrol agent for ragwort when used in conjunction with the ragwort flea beetle in the western United States.^[4]

Medical significance

The caterpillar stage of the moths growth cycle is covered in tiny venomous spines which readily release toxins into human skin following dermal contact. Although the effects of envenomation are usually limited to an itchy and/or painful rash spreading from the sight of contact, more serious symptoms such as atopic asthma, osteochondritis, dermatitis, hemorrhage, and potentially fatal renal failure, have been attributed to direct contact with the caterpillar.^[5]

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  Pupa
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  caterpillar
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  caterpillar on ragwort plant
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  Mating
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  underneath
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  Illustration from John Curtis's British Entomology Volume 5

References

1. "Cinnabar moth". A Nature Observer′s Scrapbook. bugsandweeds.co.uk. June 2007. Retrieved 2007-12-21.
2. Burton, Robert (2002). The International Wildlife Encyclopedia, Volume 1 (3rd ed.). Benchmark Books. p. 618.
3. Haccou, P. and L. Hemerik. “The Influence of Larval Dispersal in the Cinnabar Moth (Tyria jacobaeae) on Predation by the Red Wood Ant (Formica polyctena): An Analysis Based on the Proportional Hazards Model.”Journal of Animal Ecology , Vol. 54, No. 3 (Oct., 1985).
4. Coombs, E. M., et al., Eds. (2004). Biological Control of Invasive Plants in the United States. Corvallis: Oregon State University Press, 344.
5. "10 Beautiful But Dangerously Toxic Caterpillars".