Bilberry flowers early in the spring as its leaves are unfolding, and the weather in May plays a major role in determining the autumn berry harvest. The essential factor is the amount of pollinators: bilberry flowers attract many different kinds of insects, from small flies and beetles to bees and butterflies, bumblebees being the most important pollinators. If the weather is cool, however, cold-blooded insects don’t fly and pollination does not occur. Bilberry flowers are also sensitive to frost, and one cold night can destroy the whole crop when the fruit is just starting to form. Even in bad years, plants that are growing on islands and other conducive places with a similar climate are often still able to produce fruit.