Large wikis such as Wikipedia attract large numbers of editors continuously editing content. It is difficult to observe what editing activity goes on at any given moment, what editing patterns can be observed, and which are the currently active editors and articles. We introduce the design and implementation of an information visualization tool for data streams of recent changes in wikis that aims to address this difficulty. We also show examples of our visualizations from English Wikipedia, and present several patterns of editing activity that we have visually identified using our tool. We have evaluated our tool's usability, accuracy and speed of task performance in comparison with Wikipedia's recent changes page, and have obtained qualitative feedback from users on the pros and cons of our tool. We also present a review of the related literature.