“Giant Otter” The most brutal river otters are able to catch crocodiles for food.

The giant otter or giant river otter[3] (Pteronura brasiliensis) is a South American carnivorous mammal. It is the longest member of the weasel family, Mustelidae, a globally successful group of predators, reaching up to 1.7 metres (5.6 ft). Atypical of mustelids, the giant otter is a social species, with family groups typically supporting three to eight members.

The groups are centered on a dominant breeding pair and are extremely cohesive and cooperative. Although generally peaceful, the species is territorial, and aggression has been observed between groups.

The giant otter is diurnal, being active exclusively during daylight hours. It is the noisiest otter species, and distinct vocalizations have been documented that indicate alarm, aggression, and reassurance.

Its distribution has been greatly reduced and is now discontinuous. Decades of poaching for its velvety pelt, peaking in the 1950s and 1960s, considerably diminished population numbers. The species was listed as endangered in 1999 and wild population estimates are typically below 5,000. The Guianas are one of the last real strongholds for the species, which also enjoys modest numbers – and significant protection – in the Peruvian Amazonian basin. It is one of the most endangered mammal species in the Neotropics. Habitat degradation and loss is the greatest current threat. The giant otter is also rare in captivity; in 2003, only 60 animals were being held.[4]

The giant otter shows a variety of adaptations suitable to an amphibious lifestyle, including exceptionally dense fur, a wing-like tail, and webbed feet. The species prefers freshwater rivers and streams, which are usually seasonally flooded, and may also take to freshwater lakes and springs. It constructs extensive campsites close to feeding areas, clearing large amounts of vegetation. The giant otter subsists almost exclusively on a diet of fish, particularly characins and catfish, but may also eat crabs, turtles, snakes and small caimans.[2] It has no serious natural predators other than humans, although it must compete with other predators, such as the neotropical otter, jaguar, and various crocodilian species, for food resources.

Otters are voracious predators, close to being apex [top predator] in most places where they live.

So anywhere they overlap with gators this would be a pretty common occurrence. Still, this is impressive:

That’s not a small alligator, probably three or four years old and five feet [1.5 meters] long. If that’s a male otter it might be 30 pounds. That’s a very bold animal!

How does the otter know to bite the gator behind the head?

It’s actually a learned behavior. That otter has probably tried attacking smaller ones and got some bites to learn from.

Remember that crocs swing their heads side to side when they fight, so the otter wants to be entirely out of the reptile’s strike zone. Mounted on the gator’s back with teeth into the neck, that’s a smart strategy.

How does the otter actually kill the gator?

It doesn’t, not directly. First, that’s a pretty hard animal to bite through. The armor on the back is made to deflect bites from other alligators, so it’s very tough.