Moon Moth caresheet

A male moon moth _Actias heterogyna_

A male moon moth (Actias heterogyna). This photograph first appeared on the cover to the October 2008 Bulletin, the accompanying article was called "A passion for Moon Moths" by Ronald Baxter.

The Moon Moth (Actias selene) is one of the silkmoths (family Saturniidae), though its silk is of no commercial value. Live stock is easy to obtain and it is probably the easiest silkmoth to rear.

One of the caterpillars' food plants is Rhododendron. Wild forms are evergreen shrubs so leaves are easy to obtain in the winter. This makes the caterpillars ideal for rearing in winter. This is of importance for schools as it means that the problem of feeding them over the summer holiday is avoided. The caterpillars will thrive on the leaves of the holm oak (Quercus ilex) as well. This is also evergreen and therefore a small variety of food leaves may be offered in winter.

The large and very beautiful adults do not feed. They live for about seven to ten days. During the daytime they remain motionless, though if disturbed they make feeble flapping movements. At night they fly quite strongly. In the confines of a room, they tend to "flutter" along the ceiling or round a light. Unfortunately, this quickly shreds the ends of their wings. However, it is still pleasing to see them free indoors. If you do let them do this, be certain to come into the room carefully in the morning. Look for moths that have settled on the floor and carefully move them out of the way. You can hang them on furniture, curtains etc, where they will look quite stunning.

The mature caterpillar is large, green and spectacular. All of the features of an insect larva, such as spiracles, are clearly visible. They are therefore good for learning about these characteristics and for drawing.


A note of caution - unfortunately a few people are allergic to certain parts of insects. It is often the "hairs", frass (body waste) and scales, plus the more obvious protection features, such as spines with poisonous tips. Any problems that do exist are much more likely to occur with the final stage (instar) caterpillar. If you do suffer an allergic response, you should stop handling them and visit your doctor.

However, having stated this, please be reassured that cases of allergy to silkmoths are very rare. Most can be reared without trouble or danger. As far as is known, all adults are safe to rear and handle (except female Hylesia spp and certain others, and these are most unlikely to be available to the general public). Remember you should always handle living things with care and respect.

The older larvae do show a defence reaction. If disturbed they will forcible twist round upon themselves. At the same time, they fiercely gnash their mandibles. This can be heard as a clicking sound. It is therefore better not to handle the larvae once they are over 3cm in length. This is also important in order to avoid damaging the caterpillars. Their very firm grip is stronger than their body, so you may burst them if you try to remove them forcibly. If they fall, the larger caterpillars are very likely to burst.

A photograph of an Actias maenas larvae


You will need:-

  1. Larva rearing cage - such as those supplied by Watkins and Doncaster. You will also need a wide jam jar, preferably with a narrow neck, for leafy twigs. Alternatively, a range of rigid, clear plastic sandwich boxes (at least 15cm x 10cm x 7cm high) are very suitable. Perforated zinc may be needed for the lids.
  2. Kitchen towel and/or clean newspaper.
  3. Secateurs
  4. Source of food plant - check that you have access to a good supply before obtaining the insect.
  5. Pairing cage - suitable ones are available from B&S Entomological Services.
  6. Plant mister for light spraying with water in order to maintain humidity.
  7. Bleach for sterilising cages.
  8. Small, soft paint brush for handling small caterpillars.

Young larvae may be kept together in a suitably large caterpillar cage (45cm x 45cm x 45cm for 20-30 caterpillars). Alternatively, clear rigid plastic sandwich boxes may be used. This method is preferable because the boxes are easily cleaned and can be stacked on top of each other. This method also avoids another problem. Moon moth caterpillars can be cannibalistic, so older caterpillars in particular need to be kept in separate boxes.

Cages should be well ventilated. To enable this, perforated zinc may be cut to size and used as a lid. For the clear rigid plastic boxes, 3-4mm holes may be drilled in the sides - at least 10 per side.

Place kitchen towel, or other absorbent material, in the bottom of the container. If you are using a large tank, a leafy twig of food plant may be used. It should be stood in a wide jar of water and kept in place by using newspaper or kitchen towel. Make certain that the caterpillars cannot fall into the water. The smaller plastic boxes are much easier as one or two fresh leaves may be placed in the bottom. This must be done daily. The kitchen towel in the bottom should be changed as necessary, but at least once a week for young caterpillars, and every other day for older ones.

It is most important to keep the cages clean, otherwise you will getting problems with fungi on droppings, old food etc. Such fungi may also infect the caterpillars.


The adults cannot feed.

The caterpillars will feed on a variety of plants, including:-

Good results may be had by using walnut and hawthorn in the summer, and rhododendron and holm oak in the winter.

A leafy twig may be cut from a shrub or tree. Immediately cut the twig again, about 5cm above the cut end, but this time do the cut under water. This will stop air from passing into the cutting. It will therefore stay fresh for much longer, especially if kept out of the sun and wind. Keep the cut twig standing in water and remove leaves or small leafy twigs as required. (Obviously, when collecting the twigs, you should have a bucket of water with you to enable you to cut them immediately under water.)

It is most important for good later development that the young larvae have a plentiful supply of fresh food.

Humidity and temperature

The Moon Moth inhabits the tropics and therefore requires warmth. Usually, 25-35°C is best. However, in natural conditions the temperature is not static, but fluctuates (=changes), being usually cooler at night than in the day. The pupae need to be kept a little cooler and in shade - NOT in direct sunlight.

The cages may be kept adequately warm in the lounge of a centrally heated house, otherwise the use of a heat mat is recommended.

They should be kept slightly damp by lightly spraying with a plant mister each day. If they become too moist, fungal problems will probably occur. Caterpillars that are still, not moulting or feeding, are probably too dry and therefore need misting. The cocoons should also be lightly sprayed to enable emergence. The same is true for the eggs.

Eggs & hatching

The female fixes the eggs with an adhesive secretion at the time of laying. Fertile eggs are pale brown, infertile ones are bluish and their sides are clearly collapsed.

Handle the eggs carefully, preferably with a small paint brush. If the eggs are easily removed, then this can be done, but only when the shells are hard. This has usually occurred after several days. Eggs that are more firmly fixed should not be removed, they should be left in place.

The eggs are best hatched in a shady place, on kitchen towel in a container which is not airtight. Do not put food plant with them until the larvae are hatching. In any case, the first thing the caterpillar eats is the egg case (chorion).

Caterpillar care

The caterpillars go through five instars, so moult four times before pupation. Caterpillars that are moulting should be left alone, though a light misting with water might assist them.

Once the newly emerged larva have started feeding, they may be transferred to the rearing cage. This may be done either by using a small, soft paint brush, or by transferring them on a leaf. Put fresh leaves in each morning, but do not remove old leaves until the evening. The larvae will move onto the fresh food when they are ready. In this way, handling is avoided. Do check the old leaves carefully before throwing them away, otherwise you may throw larvae away as well. If you do have to move a larger caterpillar, then carefully snip off the stem or leaf it is on by using the secateurs.

Pupation & emergence

Mature caterpillars become dull and faded in colour when they are ready to pupate. They start to wander around looking for a suitable pupation site. If you are using a communal rearing cage, it is wise to move such larvae into separate containers. Fresh pupae should not be touched for at least 2 weeks, though the container should be moved into a cooler and shady place.

Adults often emerge from the cocoons four-six weeks after pupation. If they have not emerged after a longer time, then they have probably entered the overwintering state. This is called diapause. If this occurs they must be given a period of winter conditions. Often 6-12 weeks in a fridge is adequate. However, under warm conditions the moth is continually brooded, so does not enter diapause.

The emerging moths must first expand their wings. These have long tails, so the cocoons must be kept where the adults can climb to a suitable place with enough space for their wings to expand unhindered. Do not handle the adults until their wings and bodies have hardened. This should be completed in 12-24 hours.

Mating & egg laying

Pairing is best attempted during the later part of the first or second afternoon after emergence. If the female is not paired, or paired later, the eggs produced will be infertile. Males need to mate within four days after emergence or they will become infertile.

If males and females emerge at different times, they may be kept fertile for a longer period of time by placing them in a box in a cool (say 10-15°C) place soon after emergence. Remember that the adults cannot feed - they rely on food stored in the body from the caterpillar stage.

Pairing will take place in a large shoe box, but if they are disturbed they will immediately separate and pairing will fail. After pairing, a warm temperature of 25°C or more and dim light, will encourage egg-laying. However, it should be stressed that it is not an easy moth to pair, despite being very easy to rear.

Possible problems

Various problems may occur, these include:-

  1. Infection with parasites - these are usually wasps or flies. A number of maggots may emerge from the caterpillar just before pupation and they themselves will pupate. From these pupae adult parasites will emerge later. Alternatively, adult parasites may emerge from the moth's cocoon. The parasites should be collected and destroyed or they will re-infect the stock.
  2. The caterpillars may become ill from a viral or bacterial infection. The signs are dead specimens, often hanging suspended from the food plant. Any such caterpillars should be removed and disposed of and the cage cleansed thoroughly with a solution of one part bleach in three parts of water. It should then be rinsed well and dried before being used again. A bacterial infection will often quickly produce a strong bad smell. Viral infections do not do this.
  3. Insecticide on the food plants may kill the caterpillars. Be certain that the food you use is free from chemical sprays. The key sign of contamination is the caterpillars showing uncoordinated wriggling movements.

Do remember that healthy, well-fed stock kept in clean conditions is unlikely to suffer from infections. However natural mortality can occur for several reasons, such as being bitten by another caterpillar, failure to moult etc. If several larvae die in close succession, then it is more likely to be an infection. In this case, clean the cage as stated above.

Further information on Butterflies and Moths.

Essential reading from the Amateur Entomologists' Society

Remember: it is important that you know the needs and requirements of your pet before you obtain the animal. You should never, ever obtain an animal before researching its needs and preparing the housing and conditions.

Bug Club logo - join the Amateur Entomologists' Society

Want to know more?

If you want to know more about insects and other creepy-crawlies then join the AES today.