Ants and cherry laurel nectaries

 On passing by a hedge of Cherry Laurel, Prunus laurocerasus, we notice ants. Lots of Black Garden Ants, Lasius niger, walking all over the leaves. We creep closer and see little round marks on the base of the leaves that the ants are paying special attention to. They are nectaries, nectar producing organs in plants, which are most commonly found at the base of flowers. In about 1% of plants (including several species of the genus Prunus, including cherries) these organs are also found on leaves and are called 'extrafloral nectaries'. Extrafloral nectaries are part of a mutualistic relationship between plants and ants, in which both parts benefit. The plants give away the sweet nectar which feeds the ant, and in turn the ant defends the plant. By visiting the plant to obtain nectar ants come across herbivorous insects, particularly caterpillars, that might feed on the leaves, and prey upon them.
 Other nectar-loving insects take advantage from this easy to reach nectar production, and often, bees and bumblebees are found feeding in nectaries. Bees and bumblebees behave in this case as 'nectar robbers' as they do not benefit the plant at all (unlike when they feed on the floral nectaries). In this case, the ant is the one benefiting the plant. If you like the bright green, glossy leaves of the cherry laurel to stay that way, you might want to leave these ants well alone.

Ant feeding on a nectary. There is another pale, round nectary just above the ant.

Male Bombus pratorum visiting the cherry laurel