Callosity and cyamids on a right whale
Sascha Glinka/New England Aquarium

Close-up of cyamids
Close-up of cyamids
Scott Kraus/New England Aquarium

Right whales have large patches of raised tissue on their heads, called callosities (Kah-laus'-eh-tees). Some people confuse the callosities with barnacles because they appear to be white. Actually, the callosity tissue is dark like the whale’s skin, but it is infested with light-colored cyamids  (Si-am'-ids), or “whale lice.” Millions of these cyamids live on the whale’s head and can obscure the underlying callosity. Because they are light in color, they provide contrast against the black skin serving to define the outline of the callosity.

The placement and pattern of the callosity is unique to each individual and is how scientists distinguish one right whale from another. The callosity begins to emerge shortly after birth, but the pattern is not well established until 7-10 months later. Although the height of the callosity can change throughout a whale’s life (i.e. grow upwards and break off repeatedly), the placement of the callosity on the whale’s head typically remains stable. In rare cases, some callosity tissue on adult whales develops in new places or disappears.

Other things that distinguish right whales include