THE GLASSWING - Greta oto
The Glasswing has got to be one of my favorite species for flying in the tropical house during the short-day months in Europe. A central-American species (Costa-Rica, Panama, Ecuador, Venezuela), it has been well established in captivity in Britain now for the past 4 or 5 years. From stocks originally brought in by Stratford-on-Avon Butterfly Farm (see members links), a number of others [John Tampion, Bob Bellis, Geoff Gray] have succeeded in maintaining massive breeding stocks of this dainty but surprisingly long-lived little butterfly. The foodplant for Greta oto larvae, is Cestrum, a genus of Tropical & sub-tropical shrubs commonly found in the West-Indies, Canary Islands and much of Southern Europe as a decorative garden shrub. There are several species of Cestrum suitable for rearing oto larvae, each plant requiring slightly different conditions. A short description of each of the obtainable Cestrum sp. follows:-
Cestrum elegans is the one you are most likely to come across. It is commonly sold as a "house" or conservatory plant which can be put outside on the patio in summer. In the Garden ventres, you'll find it as Cestrum "Newellii" or "Purpurea". It is not the best foodplant for raring Glasswings, but it will suffice and with the Dutch growers knocking loads of these out each year, it is quite cheap.
Cestrum parquii (Willow-leaved Cestrum) is another species, although harder to find, it is said to be hardy in the southern & sheltered parts of Britain, so you may be able to grow this outside. Again, not the best foodplant, but the larvae do okay on it and it thrives under hothouse conditions.
Cestrum nocturnum is the best foodplant, although this plant needs more heat than the others and is definately NOT hardy. I grow it under hothouse conditions, in peat compost or in a limestone soil and it thrives. Medium humidity and shelter from direct sun gives the ideal conditions for both Cestrum nocturnum and Greta oto. it does best at 75-85 F. and puts on masses of growth in the spring when numbers of Greta are building up (March-June). By the height of summer, the plant is still growing well, but it's far too hot and light for the Glasswings which tend to do less well during July, August & September. This is generally the time to cut numbers down, and rest the plants, giving them time to put some new growth on. C.nocturnum is not an easy plant to find, but you may be able to beg a cutting or small plant from one of the big butterfly houses or a member who grows it. Seeds are available, but of course you have to sow this year, to use next year or the year after......... [Pictures of Cestrum nocturnum shrub and flowers are opposite >>>>>. Click on pictures.]
Breeding: Greta oto is generally available in all stages so the choice is purely financial and dependant upon how much leaf you have on your Cestrums. The hardest part of the whole process, is getting the butterflies to pair. It's just a matter of getting the conditions right, I don't think there's any one particular factor. General conditions are: Flight area of at least 2 metres cubed (2x2x2) stocked with as much Cestrum as possible, plus as many nectar-plants as you can get in there (Lantana, Pentas, Heliotrope), plus put some little pads with a fruit sugar (fructose) solution in as well, any scraps of rotten fruit on a feeding tray as well, not too light (no direct bright sunlight in summer), temperature 75-85F, Humidity 70-85% and you should not be able to stop them from breeding! Pairings usually occur late afternoon and last for ages. The eggs are laid in singly on the underside of the leaves and hatch in about 5-10 days. The larvae take 25-30 days depending on temperature, the pupae 5-10 days ditto. Well fed, the butterflies will last for at least 6 weeks, (and I suspect maybe as long as 12 weeks), and they don't damage easily, despite their fragile appearance. Along with the Heliconids and Caligo spp, they are amongst the best species to fly in winter. [P.W.B].