In 2025, a humpback whale hit the headlines when it briefly trapped a South American kayaker in its mouth, only to promptly spit him back out again, says Helen Pilcher.
That’s a big mouth, but it’s not as big as that of the bowhead whale. Its orifice is even bigger, and at 5 meters long – one third of the bowhead whale’s total body length - it is, undisputedly, the biggest mouth in the ocean.
Bowheads and humpbacks are both baleen whales, whose enormous cakeholes have evolved for filter feeding. Bowhead whales maintain their mass by consuming around 300kg of krill and other tiny ocean critters per day, which they sift from a whopping 80 million litres of water.
This is done by passing the water through keratinous comb-like structures, called baleen plates, that hang down from the upper jaw. The baleen plates of the bowhead whale are up to 4 meters long, and its upper jaw is arched to accommodate them.
On land, meanwhile, the award for biggest mouth goes to the hippopotamus. These famously grumpy animals, native to sub-Saharan Africa, dine mainly on grasses, but their enormous jaws have evolved for defense and dominance.
When closed, the mouth may not look like much, but when open wide, at an angle of over 100 degrees, the hippo has a gape of 1.2 meters. This is achieved by a combination of powerful muscles and unique jaw anatomy. The orbicularis oris muscle, which surrounds the mouth, unfolds like an accordion to facilitate extreme stretching, whilst the jaw joint is far back in the skull, to enable a large range of motion.
When the size of the mouth is considered relative to body size, however, there is another animal deserving of an honorable mention.
The pelican eel may only grow to around a meter long, but when you exclude the creature’s whip-like tail, its mouth is actually bigger than its body. The pelican eel can even swallow prey that is larger than it is.
This Tardis-like achievement is made possible by a loosely hinged lower jaw, with billowing folds of stretchy skin that unfurl to create a balloon-like structure when the eel is pursuing prey, such as squid. Few people, however, ever get to witness this spectacle. The pelican eel is a deep-sea dweller. It lives in waters up to 3 kilometers deep and so is rarely filmed, yet now its big-mouthed reputation precedes it.
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Top image: humpback whale feeding © Getty
