Sunday, 8 November 2009

Butterflies of Bristol 3: The Glasswings

At this time of year the most prominent butterflies to be seen in the butterfly house are the clearwing butterflies. These butterflies (we have the Frosted Glasswing Greta oto) belong to the Ithomiini, a subdivision of the milkweed butterflies Danainae, which in turn belongs to the gigantic family Nymphalidae. Butterflies of this group are often distasteful to predators as they sequester toxic alkaloids from the larval foodplants, which mainly in the case of the Ithomiines are members of the nightshade family Solanaceae. Some however do not depend on the larvae as a source of toxins; instead the adults obtain alkaloids from flowers or rotting leaves. This is especially the case with the males, which also use the toxins as pheromones in their courtship of females.

Our glasswings originate from Costa Rica, but the species has a large range and apparently even migrates long distances. They breed very successfully here in the house, laying eggs on the Tropical Nightshade (Cestrum sp,) plants. We have to be careful to control the number of larvae, as otherwise the plants would be stripped quickly. In the wild their numbers would be controlled by various parasitic wasps.

The life cycle is very quick, going from egg to adult in only a few weeks. They fly even at low light levels, when other butterflies will settle for the night, so in the winter months they are the most obvious to our visitors. Last winter they came through a cold snap caused by a failure of our heating system apparently completely unaffected.

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