Actias isis — “Sulawesi moon moth”

Let there be no argument; Actias isis is one of the most beautiful silkmoths that can be found on this planet. This species is endemic to Sulawesi island only and is found nowhere else.  It belongs to a group of moon moths that include Actias maenas (Asia mainland, Malaysia, Indonesia), Actias groenendaeli (Sumba, Flores, Timor), Actias philippinica (Philippines) and Actias ignescens (Andaman islands). It seems that the evolutionary lineage of this species was scattered and isolated on several islands that diverged from the mainland, diverging into a few endemic species  that are restricted to these islands. Interestingly, cocoons and eggs of this species are often exported to other continents for hobbyists to breed; while it is currently known how to reproduce them in captivity due to hobby breeding, very little of their ecology in the wild still remains known.  However, in captivity it exihibits a degree of polyphagy and can be raised on a multitude of plants that do not grow in Sulawesi where it lives. Thus, it can be assumed that in the wild, this species is polyphagous on a greater number of host plant species aswell.

dsc03817Actias isis: left is the female, right the male! The sexual dimorpism of this wonderful species is striking.

  • Difficulty rating: Moderate (Easy to raise, difficult to pair)
  • Rearing difficulty: 6/10 (From egg to pupa)
  • Pairing difficulty: 8/10 (Archieving copulations)
  • Host plants: Amber tree (Liquidambar), Eucalyptus, rose (Rosa), hawthorn (Crataegus), hornbeam (Carpinus betulus), 
  •  Natural range: Sulawesi of Indonesia (only this island)
  • Polyphagous: yes 
  • Generations: Multivoltine (continuously brooded in captivity, possibly bivoltine or univoltine in the wild)
  • Family: Saturniidae (silkmoths)
  • Pupation: Cocoon (silk encasing)
  • Prefered climate: Tropical (warm and humid)
  • Special notes:  Very easy to raise, but difficult to pair. Pairing is difficult with old adults, most pairings I have seen were from fresh females and 1 to 3 day old males. It is populair with breeders, but despite that we don’t know too much about the biology of this moth in the wild.
  • Estimated wingspan:  120 – 150mm (large)
  • Binomial name: Actias isis (Sonthonnax, 1897)

Actias isis is a species of moon moth that is endemic to Sulawesi and the Banggai-islands. Mysterious in nature, not much is known about it’s lifecycle in the wild, although it is easy to reproduce in captivity.  Yes, I do consider this species to be easy – in the breeding community it has been described as hard to rear and breed, but I suspect this is due to a lack of consistent information. Hopefully this caresheet can improve upon this.

First of all, they do accept a wide range of host plant. For the best results, I recommend using Liquidambar (Amber tree) or Eucalyptus – this years optimum result with the biggest adults and lowest mortality.   They are also able to feed on Prunus lusitanica (Portugese laurel) with mediocre result, resulting in smaller adults and more deaths.  They are also known to take Salix (willow), Crataegus (hawthorn), Rosa (rose),  Quercus (oak), Ligustrum (privet) with unfavorable results – which means these plants should only be offered if no better options are available. They may cause in all the larva dieing or refusing to feed at all – and if they do, in (small) adults with low vitality or deformities.  However, if you have no other options you can try, and in some cases the larvae will still make it to adult moths. I have seen other breeders raise them on hawthorn (Crataegus) and rose (Rosa) with suprisingly good results, resulting in big, healthy larvae and adults that reproduced. However, such good results are difficult to reproduce, and they are more inclined to fail on those plants than not; thus that does not automatically make them good host plants to use.  Some strains also seem to tolerate “weird” host plants better than others. It could be that a generation raised on Salix will produce a second generation that is better adapted to feeding on Salix, for example: making them increasingly easier to breed on these alternatives, as they are increasinly modified and adapted to captive breeding due to selective breeding. Last but not least, they are also reported to eat hornbean (Carpinus betulus) and bird cherry (Prunus padus) with mediocre to bad results.

If you have Liquidambar (I use styraciflua), please use it, in my opinion it is their best host plant by far and will result in minimal losses and very large larvae. I have reared great broods with almost no losses at all on Liquidambar many times! Eucalyptus and Prunus lusitanica seem good alternatives but keep in mind that all other mentioned plants can be a gamble.

 Fat and healthy fully grown caterpillars of Actias isis, reared on Liquidambar 

This species, being tropical in nature, will produce continuous generations in captivity. Cocoons will generally emerge after 1.5 months. Some people say raising them is difficult but I disagree. Actias isis is simple to raise in fact – the key is getting the host plant right. They are very polyphagous and will feed on a ton of host plants that will never give great results. Of course experimentation is still encouraged as there may be a lot of plants out there that give good result but have not been tried before. But for succes, I greatly recommend Liquidambar styraciflua.

Pairings, which may be the hardest part of rearing this species, can be tricky to archieve sometimes. It is said that males require a lot of flight space to locate the female. They also need a little bit of airflow, and the female needs to be quite fresh.

Unfortunately, males of this species do not last up to their full potential as they are very hyperactive and frantic flier and will become worn out, “ugly” and damaged within a few  days of emerging from their cocoons. The long tails which are very fragile, are often broken when the animals are handled due to them dropping themselves on the floor and flopping around as a defensive mechanism. However it also happens naturally as the moths fly a lot. This is not only an “aesthetic” problem: most ugly moths do not care, and are able to fly and pair with no problems. However in the case of A. isis, they can damage themselves quickly to the degree where it becomes impossible for them to pair with a female. Not only will they damage their wings, but they can also quickly lose ‘feet’ on their legs (their claws, or rather tarsal claws). Without tarsi, the moths have no grip on any surface and cannot climb to reach females. In some cases, their antennae are partially destroyed too hindering their senses they need to locate a female, an wings can be damaged to the point that it impairs their ability to fly.

For breeding purposes it is best not to handle them excessively, especially if they are freshly emerged, because the stressed moths will drop themselves to the floor and crash themselves into objects. Adults will preferably pair in warmer conditions; room temperature works and temperatures higher than 21C are appreciated. Ventilation is also important. They can be paired in netted cages/aerariums, or in larger flight spaces. Some breeders have had succes by helping the “helpless” males locate a female. This is done by placing the female in an easily accesible place (the floor of if the males cannot climb) or by providing sticks and objects that provide better grip and do not damage their tarsi. This species can also be handpaired, but I never had succes doing this with Actias isis; when handled they will twist and contort their abdomens, which makes connecting them a struggle.

A male of Actias isis, only a few days old. Ugly? Yes, but I think a good breeder will not care much about that, even though less photogenic; it is quite normal. What is worse that some males are impaired in their ability to pair naturally because of their sustained damage. 

Larvae are best reared in airtight plastic boxes up until the third instar (L3) and then sleeved/caged loose on the plant (perhaps bottled host plant) because the mature larvae require a lot more airflow and may become ill in boxes. However, if kept clean, they can be reared in plastic boxes just fine, just with more care. This species takes a reasonably long time to develop.

Actias isis, in my opinion, is more slightly more ensitive in in captivity than the average Actias species, and may quickly die if the conditions are not optimal and to their liking. It is however a  species that can be raised by beginners from eggs to adult moths in my opinion, but only if they are very careful and follow these instructions well.  However, it is the pairing of the adults and completing the cycle that can be the true challenge with breeding them. It also seems that after a few generations the bloodlines of this species are generally wiped out in captivity; it perhaps does not tolerate the inbreeding very well. It shares this trait with Actias maenas and other species from the same evolutionairy branch (probably extending to groenendaeli, ignescens, phillipinica, etc.  though there are hardly any breeding reports  on those thusfar).  Although first generations will actually pair with brothers and sisters, each generation will stop being attracted to eachother exponentially, as their pheromones start to smell to similar, reaching a point where no moths will pair anymore. It may also be that the room lacks ventilation and that the male has trouble locating the female if her scent has filled up the entire room. Males are active at night; females hardly move at all if not paired and prefer to sit still and disperse pheromones (“calling” the males).

Eggs hatch in 10 to 18 days time.

First instar larvae (L1) of Actias isis feeding on Salix (willow)

The first few instars can be reared in plastic boxes without any problems. This species seems to tolerate the high humidity of plastic containers well; many silkmoths, even tropical ones, will quickly become infected and turn into ‘soup’ when raised in closes boxes with no ventilation at all, due to pathogens overwhelming them (bacteria, fungi) and due to high humidity triggering illness and infections. However, Actias isis seem to cope well with such conditions. Yes, sure, these larvae can be sensitive; however one must be mindful of other conditions than the usual ventilation issues. Those include proper hygiëne; no wetness or condensation (note: they can be very humid, but that does not mean they have to be wet), no overcrowding, and the correct food.

This setup would be a big “no-no” for the majority of silkmoths; Actias isis however copes just fine with being raised in plastic containers.

Actias isis can be raised from egg to cocoon in 1.5 to 2.5 months. If reared colder than room temperature, larvae will be out of their confort zone, but will survive regardless – it just takes them longer to grow. Development time does not only depend on temperature but also host plant quality and quantity.

Actias isis on Liquidambar

actias isisActias isis male, wonderful and large

The larvae of this species can grow reasonably big and weigh around 15 to 20 grams before cocooning (personal observation; not representative for  the situation in the wild).

Actias isis: 18 grams

All in all, Actias isis is a wonderful endemic species, that can be raised by anyone with some basic moth breeding experience. Below some video material (subscribe to my channel for more) of a male, larvae and a female: 

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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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