Notes on rearing the Scarlet Tiger moth Callimorpha dominula (L.)

Don McNamara

I have bred this delightful insect, on and off, for many years, but continuously so since 1994. I hope the following notes will be of use.

This moth has been the subject of extensive and continuous study since at least 1928 - the studies being mainly concerned with the frequency of three forms in a discreet colony: dominula, medionigra and bimacula - and possible considerations affecting their appearance. The main focus of study is the colony at Cothill reserve in Oxfordshire.

I obtained some larvae in 1994 by a circuitous route, but whose origin was indeed Cothill. Briefly, Cothill offspring, containing the three forms were transported to a suitable site near West Kirby in 1961 by P.M. Sheppard, in order to compare observations made at Cothill. The resultant colony was "lost" for some time and discovered by Sir Cyril Clarke in 1989. A friend of mine, Alan Cronin, obtained a few individuals from this colony and bred some on, passing a few to me. Luckily all three forms are still extant in my stock.

Generally the Scarlet Tiger is very easy to breed - with the critical time being the over-wintering period of the larvae, during which most losses occur. Indeed, this is the crucial period for most of the Arctiids, as Reg Fry pointed out in 57 (416): 25-28, (February 1998) of the Bulletin.

Larva of the Scarlet Tiger

Plate 1 - Larva of the Scarlet Tiger

I house the larvae in rectangular cages. The usual size of each group is about fifty to start with. I have five cages indoors, in an unheated room. The cages are wood-framed, net-covered with a plywood base, inertial doors at the top and front - with the front door having glass instead of netting, for observation. The size is approximately 12 inches (30.5 cm) cubed. There are two outside in the back garden, raised up on a table by a corner fence, which is a bit of a sun-trap and with minimum wind disturbance. The outside cages are of the same type but larger - being of a rectangular shape - three feet high (91.4 cm), two feet deep (60.9 cm) - and with the same width as depth. They face the sun for about half the day and are in shadow for the rest.

The "not all eggs in one basket" policy limits the effects of possible infection - which can wipe out whole groups. One of my indoor groups has perished during last October (1997) as the result of my introducing a small batch of Cream-spot Tiger larvae, Arctia villica, which also succumbed. (I should have known better!) I also separate batches if they are of particular interest and are the result of contrived parings: such as dominula x medionigra, medionigra x bimacula, etc.

As mentioned earlier, the winter period is the most hazardous for larvae. In the wild, observers' estimates vary from 35% to 80% losses. I would say that my loss rate is on average 40% - very frustrating. Most of the larvae that do perish do so between November and the end of January. Once they come and feed, even for an hour or so, they seem to be more successful. The high mortality rate in my stock, despite being safe from the usual predators, might also be caused by inbreeding. An indication of this is reflected by the lowered fertility rate of the ova from those lines that I have "pushed" - for my own purposes.

Generally it is a good idea to raise livestock in as "natural" as possible conditions, hence the outside breeding area, which is acted upon by the normal elements of the British weather. Understandably the garden-reared insects have the normal seasonal phases - whilst those indoors mature up to four weeks earlier. I have not tried to get two broods per year, though I might have a crack at continuous breeding in a heated cage this year.

In the wild the larvae are found in damp places, associated with Symphytum officionale, comfrey, often near rivers or streams - but even in more open areas where there is a considerable dewfall, which seems to suit them. The months of April and May are a good time to search for them because they seek out the sun and are easily spotted on the uppersides of their larval foodplants.

I spray the foliage in my cages once a day during warm weather (allowing it to dry out before the next spray), and I am sure that these caterpillars drink because when they come upon droplets of water they lower their heads till touching them - in fact, several of them may gather round the droplets.

Unlike when rearing the Garden Tiger moth, Arctia caja, which needs to be kept dry, I put a small margarine tub full of water into the indoor cages into which a pad of cotton wool is immersed and cover this with a clean handkerchief, held by an elastic band, which keeps the top wet but allows the larvae to walk across without being caught up in the cotton wool fibres. This allows some moisture to permeate the atmosphere whilst providing a drinking trough. I don't do this for the outside cages because they get rained on. I have net-covered holes in the bottom for draining off.

The main foodplant in the wild, for the larvae in the UK is comfrey, Symphytum officionale, but 43 different foodplants have been recorded. I generally feed mine on blackberry, Rubus fruticosas, and common nettle, Urtica dioica. I have sleeved them out on sallow, Salix cinerea, on which they seem to do well. Blackberry is available all year round and in many areas you can get nettle in the winter too, especially in the sheltered patches of woods. All plant material introduced into cages should be thoroughly inspected for spiders and other potential predators.

The caged plants are bottled - with the tops well-plugged against suicidal caterpillars and are replaced periodically with fresh foodplants. I have found that if you use nettle the plants will stay in good condition for longer if part of the root is included. Always carefully check curled leaves before throwing them away, a favourite hiding-place for larvae. Also it is useful to have crumpled tissue or toilet paper for them to inhabit; this has the advantage of being sterile and does not usually contain potential predators.

I am not sure if there is a real diapause in this species, because during warm periods either outdoors or indoors larvae will become active - therefore my golden rule is always to have fresh food available. When putting sprays of nettle or bramble into cages it is useful to cut long lengths, particularly of bramble, so that you can wrap it around the inside, ensuring that the top and bottom of the cage has some leaf material available - particularly the side of the cage which is nearest to the light source. This will ensure that larvae will find the foodplant.

When the larvae have fed-up and reached maturity they will wander about the place, show little interest in food, and spend long periods being quite still. Prior to pupating they darken and shrivel slightly. Do not panic. Preparation is all. My method is to have an emerging cage (or cages) ready (same dimensions as the indoor cages), and prepare a small tray with some corrugated cardboard at the base. Larvae will spin loose webs and then bunch - usually in an upper corner of the cage frequently across the entrance. Individuals may pupate anywhere so check all material to be removed. Pupation occurs in the wild from the end of May. It lasts for approximately ten to fifteen days.

I have no evidence of cannibalism in this species - but when rearing the Garden Tiger, Arctia caja, I have seen soft pupae eaten by the larvae if there is a scarcity of foliage. So make sure that there is plenty of the larval foodplant - just in case. The Garden Tiger's larval eating habits are well-known - virtually everything, including potato peelings, privet and, when I was considerably younger and at school, I fed a brood on orange peel to see if it would improve the colour. Happy days!

At first the pupae are whitish-yellow and will darken as they harden. When they have hardened (a couple of days usually) I remove them and place them in the grooves of the corrugated cardboard. I place a stout sheet of paper above them, but not touching, ensuring that there is space at the edges for the newly-hatched moths to clamber out and make their way to the vertical sides of the cage to straighten their wings. This sheet is sprayed - to keep the atmosphere damp, perhaps more than once a day if the weather is hot.

When you remove pupae from their protective webs there is a higher chance of dehydration. (The point of removing them is that in the artificial environment of the cage the bunching may cripple the pupae and also hamper the emergence of the adults.) The balance between dehydration and being too damp thereby causing mould is one of delicate calculation - but allowing things to dry, only for a short time, inhibits mould. Moths hatch out in late June and July in the wild and the best period to see them is the second or third week in July. Of course warm or cold years will either advance or retard these times.

The Scarlet Tiger moth

Plate 2 - The Scarlet Tiger moth

In the emerging cage a selection of nectar-bearing flowers should be available, the most successful are: Candytuft (the annual cultivar); Buddleia, Buddleia davidii; any scabious species; Red valerian, Centranthus ruber; Knapweed, Centaurea nigra. When flowers are cut and placed in water they cease to renew their nectar, so spray them daily with either water or water with a 10% sugar content. The moths are great drinkers and will take moisture from the damp netting walls as well. Although they will pair and lay eggs without feeding the results are always better when the moths are well-fed. And it is always good to watch them drinking. The emerging cages are on hand for me to select the forms required - the resultant larvae will then be placed into different rearing cages according to the "plan".

Originally published in the Volume 57 of the Bulletin of the Amateur Entomologists' Society.

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