In terms of the number of humans killed every year, mosquitos by far hold the record, being responsible for between 725,000 and 1,000,000 deaths annually.
#1.
Close up of Mosquito (Aedes aegypti) sucking blood on human skin. The mosquito is the single deadliest, most dangerous animal in the world and also one of the smallest. Mosquitoes are estimated to cause between 750,000 and one million human deaths per year.
Ungainly as it is, the hippopotamus is the world's deadliest large land mammal, killing an estimated 500 people per year in Africa. Hippos are aggressive creatures, and they have very sharp teeth. And you would not want to get stuck under one; at up to 2,750kg they can crush a human to death.
Killer Whale (Orcinus orca)
Apex predator – and one of the world's largest carnivores – orca are also known as killer whales, though they are actually the largest animal in the Delphinidae family of oceanic dolphins. At 8 meters long and 5,400 kg, an average-sized orca can eat up to 230 kg of food a day.
What would it take to kill them all? A lot.
Watch: Dracula ant's killer bite makes it the fastest animal on Earth. The Dracula ant can strike 5,000 times faster than the blink of an eye, beating the old equivalent speed record by a factor of three. The jaw of a Dracula ant goes from 0 to 200 miles per hour in 0.000015 seconds.
There are 13 species of crocodiles (from the order Crocodilia), all of which can be found in the tropical regions of Africa, Asia, Australia, and North and South America. Around 1,000 people are killed each year at the jaws of opportunistic crocodiles.
Animals with no natural predators are called apex predators, because they sit at the top (or apex) of the food chain. The list is indefinite, but it includes lions, grizzly bears, crocodiles, giant constrictor snakes, wolves, sharks, electric eels, giant jellyfish, killer whales, polar bears, and arguably, humans.
The capybara, considered the friendliest wild animal, has a calm and compassionate nature, even adopting stray and runt animals, and even providing transportation on its back for birds and monkeys. Considered worldwide as the best pets, canines were one of the first species domesticated by homo sapiens.
(Canis dingo – Canis lupis dingo – Canis familiaris dingo) Dingoes are Australia's only native canid and play an important role as an apex predator, keeping natural systems in balance.
Australia's apex predator, the dingo (Canis dingo) influences the abundance and behaviour of herbivorous prey and mesopredators in arid ecosystems. The dingoes' ecological role is uncertain in more productive forested environments of eastern Australia.
Horses and cows kill the most humans every year in Australia
It really is no joke.
The Tasmanian tiger is still extinct. Reports of its enduring survival are greatly exaggerated. Known officially to science as a thylacine, the large marsupial predators, which looked more like wild dogs than tigers and ranged across Tasmania and the Australia mainland, were declared extinct in 1936.
#1: Mayfly — The Shortest Lifespan of Any Known Animal
These insects are the shortest living animals on the planet, as the adult lifespan of a fly from this species is only 24 hours.
Yes, animals do practice revenge. Chimps do it, for example. Macaques do it, too, although not directly: if they cannot attack the offender because he is much stronger, they would hurt someone weaker instead, sometimes the attacker's relative.
While it has not been proven that non-human animals do, or even can, die by suicide, many animals behave in ways that may seem suicidal. There are anecdotes of animals refusing to eat in periods of grief or stress. Some social insects have been known to defend their colony by sacrificing themselves.
To date, there's only one species that has been called 'biologically immortal': the jellyfish Turritopsis dohrnii. These small, transparent animals hang out in oceans around the world and can turn back time by reverting to an earlier stage of their life cycle.