Orgyia antiqua — “Vapourer moth”

Orgyia antiqua, the vapourer moth, is a common species of Lymantriinae (Erebidae). Originally, this species was only native to Europe – but  human activities have also introduced it in America and Asia, and possibly other places.  It comes from the temperate, northern hemisphere. Orgyia antiqua can be a very common species in parks, suburbs, shrublands, hedgerows, gardens, and at the border  of woodlands (including roadside verges in woodland paths). Globally, many species of moths are in decline because of urbanisation – but Orgyia antiqua is one of the few moths that is able to capitalise on this. These very polyphagous moths can eat hundreds of types of plants, and their life cycle isn’t as specialised as most Lepidoptera. Usually, they feed on a wide range of deciduous shrubs and trees such as birch (Betula), hawthorn (Crataegus), walnut (Juglans), cherry (Prunus), willow (Salix), bramble (Rubus), hazel (Corylus), blueberry (Vaccinium), oak (Quercus), heather (Calluna), broom (Cytistus) and more.

In reality, the list of host plants contains hundreds of species, and not all host plants can be mentioned in this article without overwhelming it with plants. The fact that this species is so polyphagous, means they can make the best of urban habitats; this species can become quite common in parks, suburbs, villages, agricultural landscape, and sometimes even in cities. The caterpillars can eat many non-native plants that are planted for decoration, but are useless to native moth species; they are found feeding on Robinia, Wisteria, Azelea (Rhododendron), sweetgum (Liquidambar), and more – and thus, they are one of the few species that thrives in these kind of environments, that have an otherwise low ecological value.

Because Orgyia antiqua can become very common in areas where humans live, it is often unfairly labeled a pest. The leaf damage that the caterpillars inflict is usually insignificant, partly because caterpillars tend to wander and feed on multiple types of plants, instead of defoliating a single one. That being said, outbreaks where the insects become so common that they are harmful to parks and gardens can happen, but are very rare, and last for a short time.

Orgyia antiqua female – the wings are reduced to little stumps

The most interesting thing about this species, is that the females are essentially wingless – although wingless is not the proper word to use here. You see, the female do have wings, but they have been reduced to little useless stumps; much like the leg bones in snakes, hipbones in whales and tailbones in humans; they are vestigial. While that seems bizarre, it is not all that unusual in Lepidoptera. This phenomenon is called brachypterism. In many moth species, even in those with ‘proper’ wings, females have a rather passive role, and may sit still for days, waiting for a male to arrive. It is the males task to locate females based on her (scent) pheromones and pair with her. In most cases, the female’s only obligation is to lay eggs after attracting a mate, and die. Brachypterism takes the same sexual roles that are already common in moths, to a more extreme level, by reducing the female to an egg-laying machine. Flying is risky if you are an insect – it may be more advantageous to stop flying at all. This allows females to have a higher body mass, since being too heavy doesn’t limit their ability to fly anymore, and stop investing energy in developing wings and muscles for flight.

Orgyia antiqua male

The males of Orgyia antiqua look more like a “typical” moth, and are rusty brown with two bright white spots on their forewings, and two large antennae. They are diurnal (they fly during the day) and can be found patrolling the area during sunny days. Their flight is very erratic, and instead of flying in a straight line, they will zig-zag a lot in order to become a more difficult to capture target. After detecting a female, males with pair with her, and the female will lay about 300 eggs. Because females are flightless, and nearly immobile they cannot locate a good spot to lay their eggs, such as a host plant. Instead, when she hatches from her pupa, she decides to stay on top of her cocoon for the rest of her life, never moving unless forced to. This is where she will also lay her eggs. It just so happens that many caterpillars spin cocoons upon their host plants, slo when the female hatches, she is already where she wants to be when she start laying eggs. Young caterpillars can also disperse through the air using the wind.

  • Difficulty ratingExtremely easy (Easy to breed)
  • Rearing difficulty: 1/10 (From egg to pupa)
  • Pairing difficulty: 1/10 (Archieving copulations)
  • Host plants:  Birch (Betula), hawthorn (Crataegus), walnut (Juglans), cherry (Prunus), willow (Salix), bramble (Rubus), hazel (Corylus), blueberry (Vaccinium), oak (Quercus), heather (Calluna), broom (Cytistus), Robinia, Wisteria, Azelea (Rhododendron), sweetgum (Liquidambar), Eucalyptus, Alnus (Alder), lime (Tilia), redcurrent (Ribes), and potentially hundreds of plant species not mentioned here – very polyphagous
  • Natural range:   Most of temperate Europe (native), America (introduced), Asia (introduced); almost everywhere on the northern hemisphere
  • Polyphagous:yes
  • Generations:Multivoltine (usually one, but sometimes more generations)
  • Family:Erebidae – Lymantriidae (tussock moths)
  • Pupation: Cocoon
  • Prefered climate:  Temperate – northern hemisphere
  • Special notes:  Often considered a forest pest; outbreaks cause destruction of forest habitat
  • Estimated wingspan: >0mm-30mm
  • Binomial name:  Orgyia antiqua (Linnaeus, 1758)

The eggs of Orgyia antiqua can be confusing. Usually,   the eggs of this species overwinter, and hatch the next year. Usually, but not always. When the conditions are favourable, the eggs can hatch the same year.  This moth can have one or two generations per year; they decide to overwinter or not depending on the local environment. Because the growth rate of moths is very dependent on temperatures, they will complete their life cycle much faster in warm years, and slowly in colder years. In colder years, they will only have enough time to produce a single generation. In warmer years, they can produce multiple. Other minor factors also may come into play such as host plant availability and competition. Based on these conditions, the eggs will decide to overwinter or not.

Generally, the eggs of the “first” summer generation should be treated as if they could hatch the same year (they can), and will either hatch the same year or overwinter.  Generally, the eggs of the “second” (extra) generation  always overwinter, and only hatch the following year in spring. Beware: this species decides to overwinter or not, depending on facts such as daylength and temperatures. When they are bred in captivity, they may experience unnatural conditions such as artificial heat and artificial light. This can cause eggs to hatch that “should” have overwintered in the wild, or vice versa.

Eggs of Orgyia antiqua

The eggs of Orgyia antiqua can be stored cold in winter, and can even survive freezing temperatures. They can be overwintered in a plastic box, envelope, or tube. To succesfully overwinter, the eggs need to be kept cold for several months.  They can be stored outside in winter if you live in a temperate climate, or otherwise in the fridge or a cool basement, ideally around 2C-7C. The colder you can keep them the better, but try to keep them frost free. In their natural habitat, the eggs can withstand freezing temperatures, although prolonged exposure to frost may impair their health in the long term.

Eggs of the overwintering generation will only hatch if they have been kept cold for months, and are then warmed up. Non-overwintering eggs will hatch if kept warm all the time. Room temperature (21C) is more than enough, since eggs hatch early spring during the first sunny days, when it can still be chilly outside.

Orgyia antiqua eggs hatching

After about 3-4 weeks of warmth, very small caterpillars will burst from their eggs. The first instars (‘baby caterpillars’) are very easy to raise on a great variety of host plants; personally I used a mix of redcurrant (Ribes), hawthorn (Crataegus), cherry (Prunus) and bramble (Rubus) to raise them. They are easily raised in plastic boxes if given fresh food plant every few days.

Orgyia antiqua L1 on redcurrant (Ribes)

On room temperature, the caterpillars will grow to reasonable sizes in about one to two months (the warmer, the faster).

Orgyia antiqua getting bigger (L3?)

The caterpillars will become fully grown in 1 to 2 months time, depending on the food plants and temperatures they experience. The fully grown caterpillars are quite pretty. Their body shows several kinds of “tufsts”; on top of their head are two ‘cephalic tufts’ that almost look like antennae, but are in reality two compact bristles of hairs that are projected from their head. The thoraric segments have four yellow/greyish tufts, and on their behind, they seem to have an anal tuft. Last but not least, the entire body of the caterpillar seems to be covered in bright red ‘warts’ (tubercules) that project patches of hair (setae). These hairs have several functions. If touched, the hairs can be mildly irritating, and may cause skin rashes or allergic reactions – their purpose is defensive. Besides keeping the caterpillars warmer, the hairs also help them sense vibrations in the air  and their surroundings,  This species is not considered to be harmful to humans, although direct skin contact may still cause irritations in very sensitive people. They can be raised from egg to adulthood in plastic containers, but avoid excess humidity and condensation. Otherwise, they grow very well if sleeved outdoors, or in ventilated cages.

Orgyia antiqua fully grown

Orgyia antiqua full size (on apple – Malus) 

 

Orgyia antiqua caterpillars

Orgyia antiqua full size on oak tree (Quercus) 

When the caterpillars finish, they spin thin, transparent, silky, grey cocoons. The ‘webbing’ is quite thin, but protected with defensive hairs. Before caterpillars pupate, they shed all their hairs and incorporate them into the silk, to give them an itchy protective coating.

After 2 to 4 weeks, adults begin to hatch from their pupae. In captivity they are very easy to pair – but remember, the males are day-flying. They just need a little bit of warmth, and if possible some ventilation, although some people managed to pair them in plastic boxes – males will seek out the females swiftly and copulate.  Males are small, brown, winged, and have two rusty brown wings with one white patch on each forewing. They zigzag wildly as they fly, making it harder for predators to capture them, but also more easily picking up pheromone trails. The small males only live for a few days, and females for more or less a week.

Females usually remain on top of their cocoons all their life – both before and after pairing – and the hairy silk will both protect her and later her eggs. Shortly after pairing, females deposit 200 to 400 eggs on top their old cocoons. When freshly laid the eggs are pale white, but over time they become brown. These eggs will overwinter, or more rarely hatch the same year.

Female Orgyia antiqua laying eggs

Orgyia antiqua female

Orgyia antiqua male
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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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