Since many people refer to "blueberries" whether they mean the bilberry (European blueberry) Vaccinium myrtillus or the American blueberries, there is confusion about the two closely similar fruits.
One can distinguish bilberries from their American counterpart by the following differences: 
bilberries have dark red, strongly fragrant flesh and red juice that turns blue in basic environments; blueberries have white or translucent, mildly fragrant flesh
bilberries grow on low bushes with solitary fruits, and are found wild in heathland in the Northern Hemisphere; blueberries grow on large bushes with the fruit in bunches
bilberries are usually harvested from wild plants, while blueberries are usually cultivated and are widely available commercially
cultivated blueberries often come from hybrid cultivars, developed about 100 years ago by agricultural specialists, most prominently Elizabeth Coleman White, to meet growing consumer demand; the bushes grow taller and are easier to harvest
bilberry fruit will stain hands, teeth and tongue deep blue or purple while eating (it was used as a dye for food and clothes), while blueberries have flesh of a less intense color, and are thus less staining
when cooked as a dessert, bilberries have a much stronger, more tart flavor and a rougher texture than blueberries
Adding to the confusion is the fact there are also wild American blueberry varieties, sold in stores mainly in the US and Canada.
These are uncommon outside of North America.
Even more confusion is due to the huckleberry name, which originates from English dialectal names 'hurtleberry' and 'whortleberry' for the bilberry.
In the Scandinavian languages Vaccinium myrtillus is called blåbär (or blåbær), which literally means blueberry.
Therefore many Scandinavians erroneously call bilberry blueberry when speaking English.
This adds to the confusion.
Since many people refer to "blueberries" whether they mean the bilberry (European blueberry) Vaccinium myrtillus or the American blueberries, there is confusion about the two closely similar fruits. One can distinguish bilberries from their American counterpart by the following differences: 
bilberries have dark red, strongly fragrant flesh and red juice that turns blue in basic environments; blueberries have white or translucent, mildly fragrant flesh
bilberries grow on low bushes with solitary fruits, and are found wild in heathland in the Northern Hemisphere; blueberries grow on large bushes with the fruit in bunches
bilberries are usually harvested from wild plants, while blueberries are usually cultivated and are widely available commercially
cultivated blueberries often come from hybrid cultivars, developed about 100 years ago by agricultural specialists, most prominently Elizabeth Coleman White, to meet growing consumer demand; the bushes grow taller and are easier to harvest
bilberry fruit will stain hands, teeth and tongue deep blue or purple while eating (it was used as a dye for food and clothes), while blueberries have flesh of a less intense color, and are thus less staining
when cooked as a dessert, bilberries have a much stronger, more tart flavor and a rougher texture than blueberries
Adding to the confusion is the fact there are also wild American blueberry varieties, sold in stores mainly in the US and Canada. These are uncommon outside of North America. Even more confusion is due to the huckleberry name, which originates from English dialectal names 'hurtleberry' and 'whortleberry' for the bilberry. In the Scandinavian languages Vaccinium myrtillus is called blåbär (or blåbær), which literally means blueberry. Therefore many Scandinavians erroneously call bilberry blueberry when speaking English. This adds to the confusion.
Vaccinium myrtillus