Galls

	Cluster of galls on a eucalypt twig Photographer - John Broomfield Source - Museum Victoria
	Gall infested eucalypt leaves Photographer - John Broomfield Source - Museum Victoria

A gall is typically a growth that can occur on a leaf or stem or root of a plant. It is simply the plant's way of getting rid of an irritation by producing tissue to surround and encase the source of the irritation. This irritation is usually the result of an insect that has been laid, or burrowed itself, under the plant surface.

Once under the surface of the plant tissue, the insect releases a chemical stimuli that irritates the plant into producing tissue. This plant tissue provides both food and shelter to the gall-making insect.

The shape and location of the gall is often characteristic of the plant and insect involved. Gall insects are typically flies and wasps but may also include true bugs and thrips. However, if you cut open a gall, it is often difficult to identify the insect that originated the gall as many gall insects are parasitised by other wasps.

It can be fun to place a few gall infested eucalypt leaves into a plastic bag and watch the myriad of insect life that emerges.