Arctia caja, also know as the “garden tiger moth” is one of the Arctiidae moths with the widest distribution in the Palearctic realm and can be found in large parts of the world including Europe, Asia, Russia and North-America. Is it a highly variable moth; each individual has different looking spots on the wings – this means each individual is unique looking! The shade of colour of the hindwings and colour of spots on the forewings also varies.
- Difficulty rating: Simple (Normally very easy rearing and very easy pairing, but sometimes larvae decide to overwinter – this can be very difficult)
- Rearing difficulty: 5.5/10 (From egg to pupa)
- Pairing difficulty: 5/10 (Archieving copulations)
- Host plants: Taxaracum, Urtica, Rubus, Trifolium, Salix, Plantago, Rumex, Iris – to name a few, one of the most polyphagous moths with 100+ host plants (can even be fed random fruit and vegetables from the supermarke such as lettuce or apple)
- Natural range: Palearctic (North America, Europe, Russia, temperate Asia)
- Polyphagous: Yes (extremely!)
- Generations: Univoltine (only one generation a year). However, can produce multiple generations per year in captivity
- Family: Erebidae (Arctiidae)
- Pupation: Spins a loose cocoon
- Prefered climate: Temperate habitat
- Special notes: Arctia caja can detect the ultrasonic sound of bats with an “ear” – like membrane, and respond to them by making ultrasonic sounds themselves, warning the bat of their toxicity
- Wingspan: 40 – 60 mm
- Binomial name: Arctia caja (Linnaeus, 1758)
The bright red hindwings of this moth serve as an aposematic warning, as the bodily fluids of this moth contain neurotoxin that may afflict potential predators that eat them. When resting, the hindwings are hidden beneath the forewings. Whenever stressed or disturbed, they will spread their wings and flash their red hindwings as a scare tactic and also a fair warning. They may also shrug their wings to make a “clicking” noise and secrete a bitter-tasting substance in order to be less palatable for predators. Some birds have been observed to eat these moths – but only in small amounts, to minimize the effects of the toxins.
Like typical Arctiids (=tiger moths) the caterpillars are hairy in appearance. Their furry tufts of hair provide protection against cold which is useful, as this species overwinters as caterpillar. They also serve to make the caterpillar unpalatable, as hairs are both hard to digest and swallow and some of the hairs also contain formic acid which may cause irratation. Instead of limiting themselves to a single host plant, the caterpillars are highly polyphagous and will feed from a wide range and mix of plants, usually low growing plants. Some examples include Taraxacum (dandelions), Plantago (plantains), Rubus (blackberries), Prunus (cherries), Trifolium (clovers) and many more. In captivity, experimenting with host plant will be worthwhile.
Notable is the highly variable individual growth rate. From the same clutch of eggs, individuals may develop as moths and reproduce, their offspring being able to catch up with caterpillars from their parental generation, that have not yet developed to adults. This picture illustrates a caterpillar, pupa and moth from the same batch of eggs. It is unusual for a single generation of moths from the same parent to remain in different stages of development.
This species doesn’t put much effort into making a cocoon, which usually consists of some loose threads covered with hairs that the caterpillar has shed. They like to incorporate objects such as leaf litter (or in captivity paper towel) into their cocoons.
In captivity these moths are quite easy to rear and breed. The caterpillars can be reared in relatively high density on room temperature. I recommend feeding a mix of Taraxacum and Plantago. Pupae do not diapause as this species overwinters as caterpillar. Can also be bred in winter. Eggs are laid in large patches, and when fertilised, will hatch quite fast.
Caterpillars spend their lives on the floor, they don’t tend to stick to their food plant but rather scavenge on the ground. So hygiene is an important factor, because this means they will dwell between their own feces if not properly cleaned.
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Citations: Coppens, B. (2019); Written by Bart Coppens; based on a real life breeding experience [for citations in literature and publications]
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