Casuarina_galls.jpg (45235 bytes)Galls: the Hemiptera are a large group of sap-sucking insects that include Aphids, Bugs, Cicadas, Leafhoppers and Scale Insects.
The Coccidae or Scale Insects come in many forms. They are best known as sap-sucking organisms that cover themselves with a waxy, protective layer and gardeners regard them as pests.
Another group of these insects rely on their host plant to provide protection. They live in hard, woody galls that are formed from aborted plant tissue. These galls have distinctive shapes and usually male and female galls have different shapes. Strangely enough gall shape is governed by the species of insect. The scale insect attaches itself to the bark of a twig or leaf surface. They set up irritation and in response woody tissue expands and encloses the insect. The galls illustrated were infesting an Allocasuarina gymnanthera (She Oak) plant. The galls probably develop at the site of female She Oak flowers. The seed-bearing cones usually occupy these positions on the stem.
The female of one species that lives on Eucalypts is surrounded by a smooth, oval, woody gall whilst the male inhabits a small, slender, trumpet-shaped gall. Male galls often occur in clusters on Eucalypt leaves. Not only does this gall insect send a message to the plant indicating its species but male and female insects are able to send a chemical signal indicating their sex.
There is a large gall that forms on some Northern Australian Eucalypts. This gall protects an insect that is eaten as bush tucker. The gall is known as a Bloodwood Apple and the insect is said to taste a bit like artichoke.