Brown bears tend to dominate polar bears in disputes over carcasses, and dead polar bear cubs have been found in brown bear dens. Wolves are rarely encountered by polar bears, though there are two records of Arctic wolf ("Canis lupus arctos") packs killing polar bear cubs. Adult polar bears are occasionally vulnerable to predation by orcas ("Orcinus orca") while swimming, but they are rarely reported as taken and bears are likely to avoid entering the water if possible if they detect an orca pod in the area. The melting sea ice in the Arctic may be causing an increase of orcas in the Arctic sea, which may increase the risk of predation on polar bears but also may benefit the bears by providing more whale carcasses that they can scavenge. The remains of polar bears have found in the stomachs of large Greenland sharks ("Somniosus microcephalus"), although it certainly cannot be ruled out that the bears were merely scavenged by this slow-moving, unusual shark. A rather unlikely killer of a grown polar bear has reportedly included a wolverine ("Gulo gulo"), anecedotely reported to have suffocated a bear in a zoo with a bite to the throat during a conflict. This report may well be dubious, however. Polar bears are sometimes the host of arctic mites such as "Alaskozetes antarcticus".