Hippopotamuses are by nature very aggressive animals. Hippos involved in attacks on other animals are often either mature bulls, which tend to be very territorial and indiscriminately ill-tempered, or females, which are quite protective of their young calves. Living on the African continent, hippopotamus coexist with a variety of formidable predators. Nile crocodiles, lions and spotted hyenas are known to prey on young hippos. However, due to their ill temperament and great size, adult hippopotamus are not usually subject to predation by other animals, except humans. Cases where very large lion prides or cooperating groups of Nile crocodiles have successfully preyed on adult hippopotamus have been reported, but this is typically believed to be exceptionally rare. Crocodiles are particularly frequent targets of hippo aggression, likely because they often inhabit the same riparian habitats as hippos. Crocodiles may be either aggressively displaced or killed by hippopotamuses. Hippos are also very aggressive towards humans, whom they commonly attack whether in boats or on land with no apparent provocation. They are widely considered to be one of the most dangerous large animals in Africa.
To mark territory, hippos spin their tails while defecating to distribute their excrement over a greater area. “Yawning” serves as a threat display. When in combat, male hippos use their incisors to block each other’s attacks, and their canines to inflict damage. Hippos rarely kill each other, even in territorial challenges. Usually, a territorial bull and a challenging bachelor stop fighting when it is clear that one hippo is stronger. When hippos become overpopulated, or when a habitat starts to shrink, bulls sometimes attempt to kill infants, but this behavior is not common under normal conditions.Some incidents of hippo cannibalism have been documented, but it is believed to be the behavior of distressed or sick hippos, and not healthy.
Although the box jellyfish has been called “the world’s most venomous creature”, only a few species in the class have been confirmed to be involved in human deaths, and some species pose no serious threat at all. For example, the sting of Chiropsella bart only results in short-lived itching and mild pain.
In Australia, fatalities are most often perpetrated by the largest species of this class of jellyfish Chironex fleckeri. In December 2012, Angel Yanagihara of the University of Hawaii’s Department of Tropical Medicine found the venom causes cells to become porous enough to allow potassium leakage, causing hyperkalemia which can lead to cardiovascular collapse and death as quickly as within 2 to 5 minutes. She postulated that a zinc compound may be developed as an antidote.
The recently discovered and very similar Chironex yamaguchii may be equally dangerous, as it has been implicated in several deaths in Japan. It is unclear which of these species is the one usually involved in fatalities in the Malay Archipelago. In 1990, a 4-year-old child died after being stung by Chiropsalmus quadrumanus at Galveston Island in the Gulf of Mexico, and either this species or Chiropsoides buitendijki are considered the likely perpetrators of two deaths in West Malaysia. At least two deaths in Australia have been attributed to the thumbnail-sized Irukandji jellyfish. Those who fall victim to these may suffer severe physical and psychological symptoms, known as Irukandji syndrome. Nevertheless, most victims do survive, and out of 62 people treated for Irukandji envenomation in Australia in 1996, almost half could be discharged home with few or no symptoms after 6 hours, and only two remained hospitalized approximately a day after they were stung.
In Australia, C. fleckeri has caused at least 64 deaths since the first report in 1883,but even in this species most encounters appear to only result in mild envenoming. Most recent deaths in Australia have been in children, which is linked to their smaller body mass. In parts of the Malay Archipelago, the number of lethal cases is far higher (in the Philippines alone, an estimated 20-40 die annually from Chirodropid stings), likely due to limited access to medical facilities and antivenom, and the fact that many Australian beaches are enclosed in nets and have vinegar placed in prominent positions allowing for rapid first aid. Vinegar is also used as treatment by locals in the Philippines.
Box jellyfish are known as the “suckerpunch” of the sea not only because their sting is rarely detected until the venom is injected, but also because they are almost transparent.
In northern Australia, the highest risk period for the box jellyfish is between October and May, but stings and specimens have been reported all months of the year. Similarly, the highest risk conditions are those with calm water and a light, onshore breeze; however, stings and specimens have been reported in all conditions.
In Hawaii, box jellyfish numbers peak approximately 7 to 10 days after a full moon, when they come near the shore to spawn. Sometimes the influx is so severe that lifeguards have closed infested beaches, such as Hanauma Bay, until the numbers subside.
The deathstalker is regarded as a highly dangerous species because its venom is a powerful mixture of neurotoxins, with a low lethal dose. While a sting from this scorpion is extraordinarily painful, it normally would not kill an otherwise healthy adult human. However, young children, the elderly, or infirm (such as those with a heart condition or those who are allergic) would be at much greater risk. Any envenomation runs the risk of anaphylaxis, a potentially life-threatening allergic reaction to the venom. A study from Israel showed a high rate of pancreatitis following envenomation. If a sting from Leiurus quinquestriatus does prove fatal, the cause of death is usually pulmonary edema. It is the 3rd most venomous scorpion in the world. The German pharmaceutical company Twyford and the French pharmaceutical company Sanofi Pasteur both make an antivenom intended for the treatment of deathstalker envenomations; additionally, the Antivenom and Vaccine Production Center in Riyadh also produces an antivenom. However, even with antivenom treatment, envenomation by the deathstalker is considered a medical emergency as its venom is unusually resistant to treatment and typically requires large doses of antivenom.
More than any documented attack, Peter Benchley’s best-selling novel Jaws and the subsequent 1975 film adaptation directed by Steven Spielberg provided the great white shark with the image of being a “man eater” in the public mind. While great white sharks have killed humans, they typically do not target them: for example, in the Mediterranean Sea there have been 31 confirmed attacks against humans in the last two centuries, most of which were non-fatal. Many of the incidents seemed to be “test-bites”. Great white sharks also test-bite buoys, flotsam, and other unfamiliar objects, and they might grab a human or a surfboard to identify what it is.
Other incidents seem to be cases of mistaken identity, in which a shark ambushes a bather or surfer from below, believing the silhouette is from a seal. Many attacks occur in waters with low visibility or other situations which impair the shark’s senses. The species appears to not like the taste of humans, or at least finds the taste unfamiliar. Further research shows that they can tell in one bite whether or not the object is worth attacking. Humans, for the most part, are too bony for their liking. They much prefer a fat, protein-rich seal.
However, some researchers have hypothesized that the reason the proportion of fatalities is low is not because sharks do not like human flesh, but because humans are often able to escape after the first bite. In the 1980s John McCosker, the Chair of Aquatic Biology at California Academy, noted that divers who dove solo and were attacked by great whites were generally at least partially consumed, while divers who followed the buddy system were generally rescued by their buddy. McCosker and Timothy C. Tricas, an author and professor at the University of Hawaii, suggest that a standard pattern for great whites is to make an initial devastating attack and then wait for the prey to weaken before consuming the wounded animal. Humans’ ability to move out of reach with the help of others, thus foiling the attack, is unusual for a great white’s prey.
Humans are not appropriate prey because the shark’s digestion is too slow to cope with a human’s high ratio of bone to muscle and fat. Accordingly, in most recorded attacks, great whites broke off contact after the first bite. Fatalities are usually caused by blood loss from the initial bite rather than from critical organ loss or from whole consumption. From 1990 until 2011 there have been a total of 139 unprovoked great white shark attacks, 29 fatal.
A shark conservationist, Jimmy Hall, reported and documented his personal encounter with a very large great white shark, nicknamed Schatzi, in December 2005 in waters off Hawaii. This encounter received worldwide attention as it remained entirely peaceful. J. Hall was at first cautious, but later swam with this shark without cage protection and touched it repeatedly while filming it simultaneously.
A group of great white sharks was believed to be responsible for an attack on a swimmer at Muriwai Beach in Auckland, New Zealand in February 2013, though initial reports placed the blame on a bronze whaler. It was the first confirmed shark attack fatality in the country since 1976.
In late 2005, researchers at the University of Melbourne speculated the perentie (Varanus giganteus), other species of monitors, and agamids may be somewhat venomous. The team believes the immediate effects of bites from these lizards were caused by mild envenomation. Bites on human digits by a lace monitor (V. varius), a Komodo dragon, and a spotted tree monitor (V. scalaris) all produced similar effects: rapid swelling, localized disruption of blood clotting, and shooting pain up to the elbow, with some symptoms lasting for several hours.
In 2009, the same researchers published further evidence demonstrating Komodo dragons possess a venomous bite. MRI scans of a preserved skull showed the presence of two glands in the lower jaw. The researchers extracted one of these glands from the head of a terminally ill specimen in the Singapore Zoological Gardens, and found it secreted several different toxic proteins. The known functions of these proteins include inhibition of blood clotting, lowering of blood pressure, muscle paralysis, and the induction of hypothermia, leading to shock and loss of consciousness in envenomated prey. As a result of the discovery, the previous theory that bacteria were responsible for the deaths of Komodo victims was disputed.
Kurt Schwenk, an evolutionary biologist at the University of Connecticut, finds the discovery of these glands intriguing, but considers most of the evidence for venom in the study to be “meaningless, irrelevant, incorrect or falsely misleading”. Even if the lizards have venom-like proteins in their mouths, Schwenk argues, they may be using them for a different function, and he doubts venom is necessary to explain the effect of a Komodo dragon bite, arguing that shock and blood loss are the primary factors.
Other scientists such as University of Washington State’s Biologist Kenneth V. Kardong and Toxicologists Scott A. Weinstein and Tamara L. Smith, have stated that this allegation of venom glands “has had the effect of underestimating the variety of complex roles played by oral secretions in the biology of reptiles, produced a very narrow view of oral secretions and resulted in misinterpretation of reptilian evolution”. According to these scientists “reptilian oral secretions contribute to many biological roles other than to quickly dispatch prey”. These researchers concluded that, “Calling all in this clade venomous implies an overall potential danger that does not exist, misleads in the assessment of medical risks, and confuses the biological assessment of squamate biochemical systems”
Brazilian Wandering Spider
P. fera and P. nigriventer are widely considered the most venomous species of spider. Its venom contains a potent neurotoxin, known as PhTx3, which acts as a broad-spectrum calcium channel blocker that inhibits glutamate release, calcium uptake and also glutamate uptake in neural synapses. At deadly concentrations, this neurotoxin causes loss of muscle control and breathing problems, resulting in paralysis and eventual asphyxiation. In addition, the venom causes intense pain and inflammation following a bite due to an excitatory effect the venom has on the serotonin 5-HT4 receptors of sensory nerves. This sensory nerve stimulation causes a release of neuropeptides such as substance P which triggers inflammation and pain.
Aside from causing intense pain, the venom of the spider can also cause priapism in humans. Erections resulting from the bite are uncomfortable, can last for many hours and can lead to impotence. A component of the venom (Tx2-6) is being studied for use in erectile dysfunction treatments.
The amount of P. nigriventer venom necessary to kill a 20 g mouse has been shown to be only 6 μg intravenously and 134 μg subcutaneously as compared to 110 μg and 200 μg respectively for Latrodectus mactans (Southern black widow). This ranks Phoneutria venom among the most deadly spider venoms to mice. The Brazilian wandering spider’s prey also includes crickets, katydids, mantids, and other larger animals, including tree frogs and lizards.
Among mambas, toxicity of individual specimens within the same species and subspecies can vary greatly based on several factors, including geographical region (there can be great variation in toxicity from one town or village to another). The venom of the black mamba is among the most rapid-acting venom of any snake species and consists mainly of highly potent neurotoxins; it also contains cardiotoxins, fasciculins, and calciseptine. Subcutaneous LD50 values for this species’ venom varies greatly. Australian toxic database provides values of 0.32 mg/kg for subcutaneous injection, 0.25 mg/kg for intravenous injection and 0.941 mg/kg for intraperitoneal injection. Ernst and Zug et al. 1996 gave it a value of 0.05 mg/kg, Spawls and Branch and (Minton & Minton 1969) both listed it as 0.28 mg/kg SC, and Brown gave it a value of 0.12 mg/kg.
It is estimated that only 10 to 15 mg will kill a human adult, and its bites delivers about 120 mg of venom on average. Although they may deliver up to 400 mg of venom in a single bite. Its bite is often called “the kiss of death” because, before antivenom was widely available, the mortality rate from a bite was 100% since this species always delivers fatal dosage of venom during every envenomation. Severe black mamba envenomation can kill a person in 30 minutes, but sometimes it takes up to 2–3 hours, depending upon many factors. The fatality rate depends on various factors, such as the health, size, age, and psychological state of the victim, the penetration of one or both fangs from the snake, the amount of venom injected, the pharmacokinetics of the venom, the location of the bite, and its proximity to major blood vessels. The health of the snake and the interval since it last used its venom mechanism is important, as well. Currently, a polyvalent antivenom produced by the South African Institute for Medical Research (SAIMR) is used to treat all black mamba bites from different localities.Due to antivenom, a bite from a black mamba is no longer a certain death sentence. But in order for the antivenom to be successful, vigorous antivenom therapy must be administered very rapidly post-envenomation. The doses of antivenom required are often massive (10–12 vials). Cases where 100 cm3 of antivenom is required are not at all unusual.
If bitten, severe neurotoxicity often ensues. Neurological, respiratory, and cardiovascular symptoms rapidly begin to manifest, usually within ten minutes or less. Common symptoms are rapid onset of dizziness, drowsiness, coughing or difficulty breathing, convulsions, and an erratic heartbeat. Other common symptoms which come on rapidly include neuromuscular symptoms, shock, loss of consciousness, hypotension, pallor, ataxia, excessive salivation (oral secretions may become profuse and thick), limb paralysis, nausea and vomiting, ptosis, fever, and very severe abdominal pain. Local tissue damage appears to be relatively infrequent and of minor severity in most cases of black mamba envenomation. Edema is typically minimal. A black mamba can rear up around one-third of its body from the ground, which can put it at about four feet high. When warding off a threat, the black mamba delivers multiple strikes, injecting large amounts of virulently toxic venom with each strike, often landing bites on the body or head, unlike other snakes. The venom of this species has been known to cause permanent paralysis if treatment with antivenom was delayed. Death is due to suffocation resulting from paralysis of the respiratory muscles.
Because of various factors, including the toxicity and high venom yield, the fact that untreated bites have a mortality rate of 100%, as well as aggressiveness, speed, agility, and size of black mamba, it is considered one of the world’s deadliest and most aggressive snake species. This view was shared by Charles Pitman.[25Nevertheless, attacks on humans are relatively rare, as the snakes usually avoid confrontation with humans and their occurrence in highly populated areas is not as common as some other African species of venomous snakes.
Moving from one of the largest animals in the world we now come to one of the smallest. As small as it is though, it is also the deadliest. It has been estimated that mosquitos transmit diseases to almost 700 million people annually resulting in 2 to 3 million deaths every year.