Whales are among the largest creatures on Earth and certainly the largest creatures of our seas. Some of these wonderful animals are the size of a small island and, like any island, they make a good habitat for a number of parasites, whale lice being the ones that are the most common company for whales.
Unlike ordinary lice, these tiny creatures are not insects, but crustaceans. They are external parasites, living on the skin, in the genital folds, around the eyes and nostrils of cetaceans, an order that includes not only whales, but dolphins as well. The relationship between the lice and their host is rather complex: the lice feed on the skin particles shed by the host, on the fluid secreted by the skin lesions they find on the host body, as well as on the algae found in abundance on and around the host’s body. They stay with the cetacean they have chosen as their living habitat for all their life.
Detailed research of whale lice found that these tiny parasites are quite choosy when it comes to selecting their host. Each species of lice specializes in a certain species of cetacean. Cyamus scammoni, for example, live only on gray whales, while Cyamus boopis live exclusively on humpback whales. One whale can host a number of different louse species, each of the species inhabiting a different part of the whale’s body, but the parasite species have only one preferred host species. This feature is believed to be a result of evolution and has been used to shed light on the genetic evolution of whales, too. Scientists think that lice were around when today’s whale species developed, some of them staying with one species, while others being forced to move to other host species.
These parasites are not lice in fact, but they received their name because they resemble lice very much. They have stout bodies that are very flat and they are 2-15 mm in length. They have four pairs of limbs, each leg equipped with a hook at the end and sharp spines that make it possible for the animal to stay anchored on the host’s body, even when the whales dives deep under the water. Lice breathe with gills, they have two pairs of gills on their head, but they are able to survive for 3 days outside the water, so they are thought to be able to breathe in other ways, too.
These parasites live in large colonies – one large whale can give home to as many as 7,500 lice at a time. They never leave the host body, which means that they don’t have a free swimming period in their life – they are born on, live on and die on their host. They multiply by laying eggs. Females have a pouch where they keep the eggs and their young, too. The pouch can contain more than 1,000 eggs at a time. The young are around 0.5 mm in length and they spend the first three months of their life climbing in and out of their pouch.