What are insect galls? Galls are abnormal growths that can arise in all
parts of a plant resulting from the work of usually immature insects and
other organisms. In a way, they are basically "plant tumors." Unlike human
tumors, galls usually do not injure their hosts to the point where the
entire plant is debilitated. The few injurious galls appear only to attack
pears, wheat, grapes, and roses.
There are over 1500 species of gall producers. However, most galls are
produced by plant mites, gall midges, and gall wasps. These creatures produce
galls to provide food and shelter for themselves. Galls can be simple
deformities consisting of a rolled leaf edge or a pouch-like growth on
the plant, or complicated structures made out of seemingly unrelated plant
tissue that are highly organized.
The principal gall producers include:
1. Plant mites - microscopic, pale yellow or translucent organisms with
slender, pear-shaped body and transverse ridges or lines. The gall producers
are in their larval stage and have 4 legs, while adult mites have 8. Mites
produce simple galls ranging from leaf deformities such as pouches or
pockets with erineum that it winters under.They're not actually insects, but they managed to wheedle their way onto this page with claims that they'd be terribly lonely if we had an entire 'Mite Galls' page devoted to them. How could we resist?
2. Aphids and plant lice - soft-bodied insects with sucking mouth parts.
These insects produce complicated galls, wintering on the bark, then hatching
out in the spring and attacking a bud to form their galls.
3. Gall midges - small delicate flies that are about 1/4 inches long,
and have antennae. The maggot larvae are what produce the galls. Gall
midges winter in galls and emerge in the spring.
4. Gall wasps (also known as Cynipids) - Wasp larvae that are formed
usually on oaks.
Although the number of gall producing organisms are numerous,
there are only a few host plants available for them to inhabit. This severely
limits the types of trees these insects can inhabit. As a result, gall
producers are very plant specific, and most of them reside among willows,
oaks, goldenrod, and asters. Galls vary in shape, size, and complexity.
The known types of galls are classified into categories: