Galls

While walking home after the most recent rainfall, I came across a leaf lying on the sidewalk. It appeared to be diseased, with tumour-like lumps dotting the suface. It looked a little something like this:

 I determined, using this website, which runs through multiple choice options for characteristics of your leaf until it can narrrow it down. But more importantly, I determined that these dots were called galls.
These galls occur on all different types of plants- where on the body where it occurs, the type of plant, and the type of insect, all effect the colour, shape and texture of the gall.

These galls were caused by a mite- translucent, and so small you need a micoscope to see them.
The University of Saskatchewan has a good, simple article on galls and the mites which cause them:

Eriophyid mites are very small, and are only visible by means of a microscope. The mites are worm like, and have only two pairs of legs. Males and females appear identical. They are poor crawlers and the primary method of population spread is by wind.

If you could see them, they would look a little something like this:

                          

Really, as unsightly as the galls can be, they do not often harm the host plant. They merely give these mites a home(or, one could say, habitat). Each mite is specific to their plant and their type of gall- they evolved together. These galls just add a harmless splash of colour and diversity to our very green neighbourhood.