Butterflies of Bristol 12: How does it work?

Butterfly houses are becoming increasingly popular all over the world, and can have a significant economic effect in the source countries for those involved on the butterfly farms, so I thought it would be a good idea to end this series, and the year, with some facts and opinions of my own about them.

The reason for their popularity is not hard to find – butterflies are beautiful, harmless (although I have seen a few people jump when a Morpho or Owl butterfly lands on them!) and comparatively easy to maintain. Basically any enclosed space can be used to house butterflies (our Butterfly House is basically a poly tunnel), provided that the internal environment is kept within the correct parameters. For tropical butterflies, this is an air temperature with a minimum of 25 degrees Celsius during the day, preferably higher, and a night temperature of at least 15. Humidity is the other important variable – for butterflies from rainforest areas it should be a minimum of 70%. Low humidity results in poor emergence, damaged wings, and shortened lifespans. Some butterflies will still fly in low light levels, especially Glasswings and Owl butterflies, but most need maximum illumination. Our butterfly house has supplementary lighting which extends the photoperiod in the winter months.

Butterflies of Bristol 11: Some new arrivals

For all those readers who are busy recovering from Christmas (you know the score – disposing of the wrapping paper, finishing up leftovers, hiding the bodies…) there are some new species just arrived from our Costa Rica supplier that can be found in the Butterfly House. Here are some brief notes on what to look for:

Tithorea tarricina. The Tigerwing

Tithorea is a nymphalid butterfly belonging to the Ithomiini, the same group as the clearwing butterflies that breed in the house. Unlike them, it is warningly coloured, from which the common name Tiger Wing butterfly is derived. Like many of their relatives, the larva feeds on members of the milkweed family Apocynaceae, with Echites and Mandevilla being reported as larval hosts, although over its vast range in Central America it probably uses several others. One odd feature is that the males are strongly attracted to bird droppings, sometimes visiting the same one several days in a row. It is believed they derived compounds from them which they use to produce pheromones used in courtship, and possibly transfer to the females to help produce healthy and viable eggs.

Butterflies of Bristol 10: Also showing

Look under the leaves of the plants as you enter the Bristol Zoo butterfly house and you may see a small, whitish snail clinging to them. These are not just any snail – they are some of the last of their kind. In fact, they come from Moorea in the Pacific, and rejoice (?) in the name Partula tohiveana.

The last fifty years or so have been a disaster for a huge number of the endemic snails of the Pacific islands. As is usual in these circumstances, human beings are to blame, in this case initially by at first deliberately, and then accidentally, spreading the Giant African snail Achatina Fulica (these will be found in many pet shops in the UK these days – and even more jam jars at school).

Butterflies of Bristol 9: Not exactly a butterfly

Not butterflies of course, but among the most spectacular of the Lepidoptera, two silkmoths (family Saturniidae) are regularly on show here at Bristol. The most spectacular, and one of the largest of all insects, is the Giant Atlas Moth, Attacus atlas. We currently have some adults on show, but unfortunately the adult phase of the life cycle does not last long – 7 to 10 days at the most. This is because, unlike butterflies, silkmoths do not feed as adults – their mouthparts are non-functional and they instead rely on the fat reserves they built up as larvae.

Silkmoths get their name because they are related, although not as closely as once thought, to the true silkworm Bombyx mori. Now split into a separate family Bombycidae, the silkworm is probably the most economically (and in history politically) important insect in the world. The silkmoths produce a coarser grade of silk than the silkworm, but many species have been used for commercial silk production nonetheless, especially in India.

Butterflies of Bristol 8: The Swallowtails

One of the most popular groups of butterflies to be seen in butterfly houses worldwide is the swallowtails (Papilionidae). Mostly medium sized to large butterflies (the Queen Alexandra’s Birdwing, Ornithoptera alexandrae is the largest of all butterflies, with a 30cm wingspan), they are also strong fliers and so make a good display. They are not usually true migrants, but they can stray long distances sometimes.

Swallowtails are grouped together by a distinctive feature of the larva, called the osmaterium. This is a forked structure that can be extended from the thorax of the larva and has a deterrent scent. The larva when disturbed will produce this and flail about to deter potential insect predators – although the frequency with which they are parasitized suggests this is not a very effective technique.

Butterflies of Bristol 7: The Whites and Yellows

Most of the butterflies with a mainly white or yellow background colour to the wings that you will see in Europe belong to the vast and widespread family of butterflies called the Pieridae. Examples that British people will be familiar with are the Large and Small Cabbage Whites, the Brimstone, and the several species of Clouded Yellows. Note that the Marbled White however is a nymphalid, and is related to the various Brown butterflies.

Pierid butterflies feed on a wide variety of food plants, but a large proportion of the European species feed as caterpillars on members of the Cruciferae (the mustard or cabbage family). The Clouded Yellows however are associated with members of the Leguminosae, especially Lucerne(alfalfa in the US).