The Tweet: “Lobsters are functionally immortal – They show no signs of aging, loss of appetite, no change in metabolism and no decline of health.”

This myth refers to a phenomenon called senescence. The origin of which seems to come from a 2007 report by Robert Krulwich, talking to Professor Jelle Atema of Boston University, on NPR: “lobsters in general show no discernible signs of aging. They don’t lose appetite, sex drive, energy, no change in metabolism.”

Senescence is the decline in function of body processes in later life. This could be the loss of reproductive function, the end of growth or the slowing down of the body’s ability to repair. All of these are seen in humans in old age, but not in lobsters. But this doesn’t equate to immortality. Many invertebrates continue to grow and reproduce throughout their lifetime. A frequent addition to this myth is that they only die by external causes, but for most wild animals this is usually the case. Animals in their old age are more susceptible to predators or disease as during the course of their lifetime they will pick up injuries or become slower. And there will always be a predator large enough to kill a lobster; usually a seal.

Like other crustaceans, lobsters have indeterminate growth. This means they will continue to grow throughout their lifetime. Lobsters grow by moulting. Initially they moult very frequently, until they reach adulthood where they moult only every two to three years. The largest lobster ever recorded weighed 44 pounds, but in theory they could grow even bigger. Continuing to grow is a huge advantage for lobsters as larger females will produce more eggs resulting in a greater reproductive success.

Moulting is a stressful and costly process. Between 10 and 15 per cent of the lobsters that die annually do so during moulting. The larger the lobster, the more exertion is required to moult the exoskeleton and therefore the more dangerous the process. Old lobsters will stop moulting altogether if the process is too difficult, showing that they are near the end of their lives. Lobsters are very vulnerable immediately after moulting when their new exoskeleton is still soft. Damaged shells can also contract shell diseases that adhere the exoskeleton to body of the lobster preventing it from moulting cleanly or even causing it to rot. It’s likely that over the course of a long natural life that the moulting process will eventually kill the lobster.

Scientists have used telomerase expression as an explanation of lobsters’ ability to continue to grow throughout their lifetime. Telomerase is an enzyme used in cell division that preserves the ends of chromosomes. This means that as cells continue to divide over the lifetime of an animal chromosomes won’t become damaged or pick up mutations. High levels of telomerase activity would therefore ensure that an animal could continue to grow healthy cells throughout its life. Klapper et al. write in their study from 1998: “High telomerase activities were detected in all lobster organs. We conclude that telomerase activation is a conserved mechanism for maintaining long-term cell proliferation capacity and preventing senescence.”

To say that lobsters show no sign of aging or decline of health in the wild is untrue. They are as susceptible to disease as any other animal and are, therefore, not immortal.