When a peacock mantis shrimp strikes, it generates the heat of a star. The crustacean retracts a spring-loaded mouthpart known as a dactyl club and puts it on a latch, like a cowboy cocking the hammer of a gun.<\/p>\n
After pulling the trigger to release the stored elastic potential energy, the club moves like a bullet to reach speeds of up to 31m per second (around 111kph).<\/p>\n
The punch is so fast that it lowers the surrounding pressure, causing water to boil and form steam-filled bubbles that suddenly implode by \u2018cavitation\u2019 \u2013 a pop of sound, flash of light and temperatures approaching 5,000\u00baC, as hot as the surface of the sun.<\/p>\n
\u201cCavitation bubbles collapse and emit an intense burst of energy,\u201d explains Sheila Patek, a biologist at Duke University in North Carolina.<\/p>\n
The bubbles can damage metal if they form around boat propellers, but \u2018smasher\u2019 species of mantis shrimp exploit this force (more than 100 times their bodyweight) to crack open snails or other packaged food.<\/p>\n
\u201cThey evolved hammers and spring-latch mechanical systems to fracture hard-shelled prey with high accelerations,\u201d says Patek, whose research focuses on fast and powerful animal movements. \u201cThey can produce up to 1,500 Newtons (N) at impact.\u201d<\/p>\n
A peacock mantis shrimp\u2019s punch holds the record for fastest strike in the aquatic world but, on land, the title of fastest gun in the west goes to the Dracula ant<\/a>.<\/p>\n The ant\u2019s ultrafast mandibles can close at 90m per second (321kph) in 23 microseconds (more than 4,300 times faster than the blink of an eye) so the vampire can bite through an insect\u2019s exoskeleton and drink its blood. But while these tiny jaws are certainly terrific, they wouldn\u2019t terrify larger creatures.<\/p>\n Are teeth a weapon?<\/p>\n Nature\u2019s most fearsome weapons are arguably the jaws of the great white shark. From computer models, scientists predict that its bite force can reach 18,216N, the highest estimate of any living species (the highest ever measured, at 16,414N, was recorded from a saltwater crocodile<\/a>).\u00a0<\/p>\n Each great white tooth also has a triangular shape, which concentrates that force over a small surface area so the predator doesn\u2019t need to press hard to pierce prey.<\/p>\n Shark and human teeth are made of slightly different materials but have similar hardness and strength, which is enough to withstand massive forces.<\/p>\n So why do great whites continuously grow new teeth?<\/p>\n \u201cWe don\u2019t know how many bites each tooth experiences or how often most sharks lose their teeth, but it\u2019s certainly not breakage,\u201d says Lisa Whitenack, a biologist at Allegheny College in Pennsylvania, who did her PhD on the biomechanics and evolution of shark teeth.<\/p>\n Instead, great whites may need to regularly replace teeth because they get blunt and lose their sharp edge.<\/p>\n \u201cIt only takes 10 to 20 bites for the shark tooth to noticeably dull.\u201d<\/p>\n The serrated structure of great white teeth also helps tear through flesh: once the predator has clamped down, it produces a sawing action by shaking its head.<\/p>\n \u201cA butter knife doesn\u2019t really catch fibres in the meat, but a steak knife has a heavier serration that can trap the fibres,\u201d says Whitenack. \u201cThe harder you push down, the less force you have to use to pull and cut your steak.\u201d<\/p>\n What can be classed as a weapon?<\/p>\n Features such as the great white\u2019s jaws and a mantis shrimp\u2019s club have evolved over millions of years into forms that seem perfectly adapted for their functions.<\/p>\n They match how the Oxford English Dictionary defines the word \u2018weapon\u2019: \u201cAn instrument of any kind used in warfare or in combat to attack and overcome an enemy.\u201d<\/p>\n But such physical instruments don\u2019t qualify as weapons under the traditional definition in biology: \u201cConspicuous morphological structures used by males during contests over access to females.\u201d<\/p>\n This means well-known examples such as deer antlers<\/a> and beetle horns. Defining weapons so strictly is problematic, however.<\/p>\n It ignores features exclusive to females, including the stingers of wasps, bees and ants, which evolved from ovipositors that were once used for laying eggs, for instance. More importantly, focusing on conspicuous male structure can overlook weaponry in living things besides animals.<\/p>\n In the plant kingdom, carnivorous species such as the Venus flytrap<\/a> can capture small arthropods. However, some scientists would argue that the plant\u2019s jaws are no more than a mechanical bear-trap, not a weapon for combat.<\/p>\n Similarly, spiky structures such as thorns, spines or prickles are analogous to barbed wire and evolved to discourage plant-eaters, which is why they\u2019re known as plant defences against herbivory.<\/p>\n But despite the fact that flowering plants can\u2019t move or attack, the group has some clear cases of traditional weapons used by males.<\/p>\n In milkweed, male pollen is contained in sacs that attach to insects and are deposited when a pollinator visits the female parts of another flower.<\/p>\n A 2014 study showed that some species have sacs with horns to block the sacs of other males from attaching \u2013 equivalent to when a dominant male mammal, such as a walrus with big tusks, monopolises mating opportunities by occupying the prime spot on a beach.<\/p>\n \u201cOur study was the first to demonstrate that plants can engage in male-to-male physical fights,\u201d says Andrea Cocucci, director of the Botanical Museum at the National University of C\u00f3rdoba, Argentina.<\/p>\n How have animal weapons evolved?<\/p>\n Weapons have evolved through natural selection because they enabled a species\u2019 ancestors to survive or reproduce.<\/p>\n This survival of the fittest can by driven by \u2018ecological selection\u2019, when changes in the environment (such as availability of prey) favour individuals who carry beneficial adaptations such as claws or talons<\/a>.<\/p>\n But features used in competition between males \u2013 such as the microscopic horns of milkweed pollen, majestic antlers of male deer and mandibles of stag beetles \u2013 are usually selected by females. <\/p>\n Such structures require energy to grow, are cumbersome to carry and are conspicuous to predators, meaning they exist because the potential costs to survival were outweighed by benefits to reproductive success.\u00a0<\/p>\n This is the theory of sexual selection first proposed by Charles Darwin.<\/p>\n \u201cThe widespread occurrence of horns in vertebrates and insects is explained by Darwin\u2019s seminal work as a product of evolution<\/a> through sexual selection,\u201d says Cocucci. \u201cTriumphant males in a fight get access to females for reproduction.\u201d<\/p>\n Does chemical warfare exist in the animal world?<\/p>\n Habitats are battlefields where organisms wage chemical warfare, too. But while some species make chemical poisons that cause sickness or death, these toxins have evolved mainly as deterrents.<\/p>\n They make an organism unpalatable and passively enter the body. By contrast, when a toxin is actively delivered by injection, via bite, sting or spray, it\u2019s a venom \u2013 a weapon for attack or self-defence.<\/p>\n \u201cPredatory venoms typically act by quickly immobilising prey, while defensive venoms generally cause rapid pain, which deters an attacker,\u201d says Ronald Jenner from the Comparative Venomics Group at the Natural History Museum in London, co-author of Venom: The Secrets of Nature\u2019s\u00a0Deadliest Weapon.<\/p>\n But while many venoms aren\u2019t designed to kill, death is often the end result. Their range of devastating effects ranges from causing internal bleeding, by preventing blood from clotting, to manipulating behaviour or liquifying a host.<\/p>\n A venom can be a mixture of toxins<\/a>, each affecting a specific molecule in the intended victim. Those molecules can vary among species, however, meaning that a given venom may be harmful in one species yet harmless in another. This makes it difficult to determine which is the worst, says Jenner.<\/p>\n \u201cThe effects of venoms are diverse, so the power of venom cannot be captured by any single measure.\u201d<\/p>\n Nonetheless, scientists often study potency through a metric called LD50, the lethal dose that would kill 50 per cent of a population of lab mice, as a model for how a venom might affect another mammal, humans.<\/p>\n But LD50 also shows why it\u2019s hard to identify the worst venom, as illustrated by Brazilian frogs that use the head as a weapon: while the venom of a Bruno\u2019s casque-headed frog is 25 times more lethal than the poison of a Bothrops pit viper, the snake\u2019s fangs<\/a> are more dangerous as they deliver more venom in a single bite.<\/p>\n