An extremely dangerous Red list abnormal that is worth a fortune on the abnormal black market.
As soon as a ferapetus egg hatches the new born will immediately go in search of a host in which it'll gestate for about an hour or so. After finding a suitable host the ferapetus secretes an enzyme inhibitor that'll sedate the host until it's fully grown. However, the human metabolism is significantly stronger than that of the other species the ferapetus encounters in the wild so a human being would be fully awake and unaware if they were the host to a ferapetus. However, the enzyme inhibitor that a ferapetus secretes will slow down the hosts photo receptors in the eyes.
The body temperature of a newly hatched ferapetus is 98.2 degrees, which means that a ferapetus could get under a human's skin without that human even noticing because their body temperatures are so close.
After the ferapetus' gestation period ends, it'll immediately kill its' host, burst out of their chest, proceed to go on a feeding rampage, kill everything in its' path, and finally go into a dormant state until its' next cycle.
When dealing with a ferapetus, the Sanctuary does their best to get the egg inside a secure container before it hatches.
A ferapetus' gestation period can be slowed if the hosts' body temperature is lowered and you can tell when a ferapetus is about to finish its' gestation period when the host starts exhaling gestation vapors.
The ferapetus needs a calm chemical enviorment in which to gestate, if the host were to be exposed to some kind of toxin harmful to the ferapetus it'd have no choice, but to leave its' current host without killing them.
In the episode "Bank Job", two thieves stole a pair of ferapetus eggs believing they were just rare works of art and sold them at a private auction. One of the eggs hatched in Monaco before the Sanctuary could secure it and the new born ferapetus killed several people. The second egg was in a safety deposit box in small town in the US. The Sanctuary team wanted to at first handle it quietly, but they soon realized they were too late. The banks air conditioner was broken and the heat forced the ferapetus to hatch from its' egg sooner than planned. Thinking quickly, Kate Freelander told everyone in the bank her and her friends were bank robbers and none of them could leave, this way the Sanctuary team had time to check everyone there and see which one of them had the ferapetus inside them so they could get it out before it fully gestates and kills everyone. Despite interference from the FBI, the local police, and an abnormal bounty hunter, Magnus and her team were able to retrieve the ferapetus and get it back to the Sanctuary with no loss of life.