HWA crawlers on a canvas beat sheet with a penny for scale. 24 May 2007, Kittery, ME.

The hemlock woolly adelgid hatches from eggs into what is called the crawler stage. This stage is minute, highly mobile, easily moved and abundant. In southern Maine crawlers are generally present between Mid March through the end of July. There is a time in that period when crawlers are not present, but because of the overlap in generations it is best to consider the whole period as potentially having mobile crawlers. Crawlers and eggs can be easily spread and cause new areas of adelgid infestation. Other life-stages require the movement of live hemlock material (such as nursery stock or seedlings) to become established.