Does Size Matter?

Why the strongest, toughest, deadliest species are more likely to be found under a microscope than in the zoo
When it comes to size, bigger does not necessarily mean better. Nowhere is this more true than in the natural world. We might marvel at […]

Art by Anna Pouncey

When it comes to size, bigger does not necessarily mean better. Nowhere is this more true than in the natural world. We might marvel at the dangers of great whites, pythons and big cats, but it’s actually the world of microorganisms that contain the real bad-boys of nature. With bacteria that can survive a nuclear disaster 1,000 times worse than Fukushima, microorganisms pound-for-pound stronger than an elephant, and pathogens deadlier than any snakebite, let me introduce you to the real superheroes of the natural world.


The world’s largest land animal, the elephant, is a clear candidate for the title of the strongest organism. Elephants consist of over 5 tonnes of pure brawn, are capable of lifting a tonne and can drag 20 times their body weight. When stampeding or during a drastic testosterone rise known as ‘musth’ (Persian for ‘intoxication’) elephants have been known to crush and kill other land mammals, including humans and even rhinoceros. The bacterial world may seem an unlikely place to find nature’s strongmen but, relative to their size, they can pull forces of epic proportions.

The miniscule Neisseria gonorrhoeae bacterium, cause of the common STI gonorrhoea, is one such species. This bacterium is capable of pulling up to 100,000 times its own body weight, the equivalent of a human being able to pull 2,000 African Elephants. The bacterium achieves this by the production of what are known as ‘type IV’ pili—filaments ten times as long as the bacterium itself that are used to crawl along surfaces and attach to cells. Research conducted by Michael Sheetz and his colleagues at Columbia University, New York, found the bacterium were capable of bundling these pili together in order to produce long, stronger pulls that were ten times more powerful than an average ‘grab’ and could last for several hours. Although the actual force exerted is tiny, relative to its body weight this bacterium has super-strength.


Some animals are capable of surviving, and even thriving, in some of the world’s most extreme conditions. The polar bear is the largest terrestrial carnivore, with an adult male weighing up to 680 kg. These stocky animals are kept warm by an insulating layer of blubber up to 10 cm thick, and a dense coating of fur. Excellent as both swimmers and hunters it seems these creatures are incredibly well adapted to extreme conditions.

But these adaptations pale in comparison to their tiny (very) distant cousins, the water-bear. These microscopic, water-dwelling tardigrades are eight-legged invertebrates, more closely related to arthropods such as spiders and insects than polar bears. They have a CV stocked full of impressive and amazing adaptations. If dehydrated, they can curl into a ball and reduce their metabolic activity to less than 0.01% of the normal levels. Like an extreme version of hibernation, tardigrades are able to be rehydrated and ‘wake up’ after periods as long as 10 years. But that’s not all. These micro-organisms are also capable of withstanding temperatures from -200 to 151 °C, a lack of oxygen, lethal doses of X-ray radiation, and even the vacuum of space. Not bad for a 1 mm long invertebrate.

Another master of survival is the hyperthermophile. A type of bacteria, these single-celled micro-organisms are known for their love of scorching hot environments, such as deep-sea hydrothermal vents. One such example is Pyrolobus fumarii. A species usually found in ‘black smokers’, chimney-like hydrothermal vents at the bottom of the Atlantic, which reach temperatures of around 113 °C—temperatures that would quickly kill even your most heat-resistant desert-dweller. Not even other hydrothermal-vent-dwellers such as the Pompeii worm can compete. Despite being the second most heat-resistant complex animal known (behind tardigrades, of course), the Pompeii worm can survive temperatures no higher than 80 °C.

Even radiation is no match for some types of bacteria. Deinococcus radiodurans can survive levels of radiation thousands of times greater than the peak level observed during the Fukushima nuclear crisis (see ‘On the Edge’, p12). In contrast, humans could not survive exposure for more than a few hours. When it comes to survival, bacteria have been the best in the business for billions of years.


Enough horror-films have been produced for us to know there are some dangerous creatures in the sea. One of the most famous underwater killers is the ferocious Great White Shark. They have an estimated biting force of up to 18,000 newtons, the equivalent of being crushed under the force of a falling Land Rover. But you don’t necessarily have to have monstrous jaws and rows of teeth to be an effective hunter. The bacteria Bdellovibrio, found in river water and soil, feeds on other bacteria. They attack their prey by colliding with them at speeds 13 times faster than a cheetah, relative to body length. They then kill their prey by entering their cells, digesting them from the inside out. Bdellovibrio’s methods might be less bloody than a shark, but they are just as nasty.

Whether it’s strength, survival, or killer instinct, the best, or possibly worst, things come in small packages.


About Holly Youlden

Holly Youlden is a 2nd year undergraduate reading Biological Sciences at Keble College.