maple bladdergall mite

Unsightly but not harmful to humans or host trees

Several generations each year. The first galls develop late spring.

Microscopic, about 1 ⁄125″

This mite is about 1 ⁄500″ to 1 ⁄125″ long and invisible to the naked eye. It is most easily identified by the shape of the gall it produces and the plant species on which it is found. This mite is found exclusively on silver maple, red maple, and sugar maple.

The pouch-type galls first appear on the upper side of a leaf in late spring. They are solitary, though there are usually many galls on a single leaf. They are hollow and globe-shaped with a hairy opening on the underside of the leaf. They vary in size but may be up to 1 ⁄10″ in height. They are green when they first appear, turning pinkish or red, and then finally black. The galls are unsightly but the tree is otherwise undamaged.

This is the only mite that causes bladder galls on these host species. It is not found on other plant species.

The adult overwinters in a crevice of the trunk or a branch. As leaf buds begin to swell in the spring the female emerges and begins feeding on a leaf bud. This causes the leaf to produce excess cells that rises above the leaf surface like a blister. The female then enters the hollow gall and deposits eggs. When the eggs hatch the young feed on the interior of the gall. In the summer the gall dries out. In fall the gall opens on the underside of the leaf. The adult emerges and searches for a site to overwinter.

Sources

Leaf with Bladder Galls

Bladder Galls