Tag Archives: dangerous animals

Shark Bites in the USA

The USA has the most reported shark attacks in the world. What could be the reason for this? Are Americans so well nourished that they taste better? Could be, but all the references I have read say that a shark attack is most probably an “accident”. The shark had mistaken the human for his more usual meal such as a seal or another fish.

One reason the United States is at the top of the list is that the U.S. has a very large combined coastal shoreline. Another reason is the increase of recreational marine activities, and recreational marine activities expose people to all aquatic dangers including shark attacks.

No doubt, a high level of reporting of attacks is also a factor. Not all coastal countries publish a complete record of shark attacks. Publishing such reports could adversely affect the tourist trade. In addition to the USA some of the other countries that have reported shark bites are Africa, Central & S Am, Australia and Pacific Islands.

In the U.S 60% of all shark attacks are reported by the state of Florida. California reports about 15%, this is closely followed by Hawaii. Most coastal states have at one time or another reported a shark attack. Most of the attacks are not fatal. Most of the attacks are done by a contact bite, then the shark swims away. The victim can be left with a maiming wound or deformity. Fatal attacks are mainly due to the bull shark, tiger shark, or the great white shark and the Oceanic white tip shark. (Pictures and information about these sharks can be found at Dangerous animals–Sharks). In recent years the entire east coast has had a growing problem with aggressive sharks. The reason for the increase is being researched.

Overall shark attacks are extremely rare – “Lightning strikes humans more often than sharks bite humans”. The International Shark Attack File reports that world wide there are 50 – 70 unprovoked shark attacks a year. The number of shark attacks is increasing because the human population is increasing and recreational use of the shark habitat, oceans and coastlines, is increasing. Even though there are 50 to 70 attacks a year the number of fatalities are low.

Wikipedia has a list of the fatal, unprovoked shark attacks in the US. The records start in 1779 up to the recent. The more recent records state the age of the victims and other information that is interesting reading and gives some explanation of the event. A summary of the records show that there were 13 deaths from 2000 to 2010. Three of the years, 2002, 2006 and 2007, did not have any deaths. The years 2001 and 2004 had 3 deaths each. So far in 2010 there have been two reported deaths due to shark bites, but the year is not over.

Dangerous animals—spiders

In this installment of the Dangerous Animals series we look at a group that is very misunderstood, and often erroneously indicted for being dangerous—spiders. In the summary chart of dangerous animals, summarized from various sources, spiders are accused of causing 6 deaths a year, on average, in North America. This is more deaths than caused by bears, mountain lions, and wolves combined, and I am highly suspicious of the figure.

In his review of the Centers for Disease Control and Prevention (CDC) data, Langley (2005) summarizes death by all sorts of wild animals, and spider bites have their own classification code, suggesting that the medical community has decided it is worth watching for. For example, the data suggest that between 1991 and 2001 there were 5 fatalities by alligators, and a whopping 66 deaths by spider. People seem to be dropping dead left and right from spider bites. What gives?

In North America, there are two types of spiders known to cause medically significant envenomations in humans: the widows and the recluse. Let’s look at each.

Latrodectus, the Black Widow

Latrodectus, the black widow, showing a characteristic pose, upside down in the web.

There are currently 30 species of spiders within the genus Latrodectus, commonly called widows in North America. The species are distributed world-wide and are on every continent except Antarctica. The venom of the widow contains neurotoxins that inhibit neurotransmission. The spiders like dark and quiet places, with bites occurring when people unintentionally grab or sit on the spider, perhaps under a porch, on lawn furniture, in the tool shed, or in gloves or other item clothing. In the past bites sometimes occurred in outdoor toilets. Symptoms of bites tend to be local and radiating pain, and sometimes back, abdominal, and chest pain, sometimes accompanied by fever, agitation, hypertension, and interestingly, priapism (Vetter and Isbister 2008). People have described it to me like a case of the flu. Untreated, symptoms can last from hours to days. Despite their infamy, death is very uncommon.

Loxosceles reclusa, the Brown Recluse

Loxosceles reclusa, a Brown Recluse female guarding her egg sac on a cardboard box in Kansas.

Few spiders generate as much passion and aversion as the brown recluse (Loxosceles reclusa). I currently live in an area where black widows are extremely common, and local people are very casual about them, but are terrified of the brown recluse. I have done many educational programs where I have displayed live spiders, including black widows, and unvaryingly I am treated to several stories by visitors about how they (or someone they know) were bitten by a brown recluse, usually with very bad consequences. (I literally had one person tell me that his aunt had her entire arm removed because of a bite). The thing is brown recluse spiders do not live here! Nothing generates fear like the unknown.

Prior to living where I do now, I lived in an area with gobs of brown recluses, and the people there were generally nonchalant about their presence, as there were almost no cases of bites resulting in horrible wounds.

Distribution map of species within the genus Loxosceles, including Loxosceles reclusa, or the Brown Recluse (from Vetter 2008).

To be clear, Loxosceles is confirmed to have bitten people and caused wounds that in rare cases take a long time to heal and can leave disfiguring scars, or even death. They are a spider of medical concern. But, having said this, the threat is far over blown.

They are named “recluse” because they like very quite areas, and can frequent homes and storage sheds in quite places. They like corners of basements, and particularly cardboard boxes. Sometimes they crawl into clothing and shoes left on the floor or in the closet. Like with the widows, people are most often bitten when they catch the spider between their body and where the spider is—the bite is defensive.

In a majority of cases, the bite results in local discomfort and nothing more. In some cases a larger wound forms that is tender, but most of these heal with minimal medical intervention, usually within days. Sometimes the wound heals slower, and in rare instances does grow large and can leave a scar. And in very rare cases (<1%) there are more significant systemic issues that can affect major organs and cause death. (Vetter and Isbister 2008).

As mentioned, I lived in an area with known recluse populations. In fact, in one case, 2,055 individual recluse spiders were captured in 6 months from one home in Kansas where the family lived for many years without a single incident attributed to the spiders (Vetter 2008). However, popular perception about these spiders is very different. Why is this?

The most likely explanation is that when the recluse was implicated in bites the most extreme cases got widely reported, heightening awareness in the public and medical community. Diagnoses of recluse bites have become common place, often in areas where the spiders have not been found in the wild, and usually without clear evidence that the symptoms presented were actually caused by a spider, or any other bite for that matter. For example, in Florida, an area without a known population of recluses, during a six year period, 844 brown recluse bites were reported: 124 by medical personnel, 198 by people seeking information about bites, and 522 from people reporting bites treated at a non-healthcare facility (Vetter and Furbee 2006). Physicians are thus occasionally guilty of “practicing Arachnology” by identifying bites, and even spider species, from clinical symptoms alone. The truth is, there are numerous conditions that have been, or could be, misdiagnosed as a recluse bite (Vetter 2008) (see below).

Given the obvious over-diagnosis and misdiagnosis of spider bites, and of recluse bites in particular, I find the assertion that 6 deaths a year in North America are caused by spiders to be highly doubtful. At the very least, this is an undeserved slam against our eight-legged friends, and at worst is misleading the public and medical community, causing potential misdiagnoses and poor treatment choices.

Conditions that have, or could be, misdiagnosed as a bite from a brown recluse (Loxosceles reclusa), from Vetter 2008.

Infections

Atypical mycobacteria

Bacterial

– Streptococcus

– Staphylococcus (especially MRSA)

– Lyme borreliosis

– Cutaneous anthrax

– Syphilis

– Gonococcemia

– Ricketsial disease

– Tularemia

Deep Fungal

– Sporotrichosis

– Aspergillosis

– Cryptococcosis

Ecthyma gangrenosum (Pseudomonas aeruginosa)

Parasitic (Leishmaniasis)

Viral (herpes simplex, herpes zoster (shingles))

Vascular occlusive or venous disease

Antiphospholipid-antibody syndrome

Livedoid vasculopathy

Small-vessel occlusive arterial disease

Venous statis ulcer

Necrotising vasculitis

Leukocytoclastic vaculitis

Polyarteritis nodosa

Takayasu’s arteritis

Wegeners granulomatosis

Neoplastic disease

Leukemia cutis

Lymphoma (e.g., mycosis fungoides)

Primary skin neoplasms (basal cell carcinoma, malignant melanoma, squamous cell carcinoma)

Lymphomatoid papulosis

Topical and Exogenous Causes

Burns (chemical, thermal)

Toxic plant dermatitis (poison ivy, poison oak)

Factitious injury (i.e., self-induced)

Pressure ulcers (i.e., bed sores)

Other arthropod bites

Radiotherapy

Other Conditions

Calcific uremic arteriolopathy

Cryoglobulinemia

Diabetic ulcer

Langerhans’-cell histiocytosis

Pemphigus vegetans

Pyoderma gangrenosum

Septic embolism

Related posts:
See the rest of the Dangerous Animals series
Pesky house bugs–bed bugs

References:

Langley, R. L. 2005. Animal-related fatalities in the United States–an update. Wilderness & Environmental Medicine 16:67-74.

Vetter, R. S. 2008. Spiders of the genus Loxosceles (Araneae, Sicariidae): a review of biological, medical and psychological aspects regarding envenomations. The Journal of Arachnology 36:150-163.

Vetter, R. S., and R. B. Furbee. 2006. Caveats in interpreting poison control centre data in spider bite epidemiology studies. Public Health 120:179-181.

Vetter, R. S., and G. K. Isbister. 2008. Medical aspects of spider bites. Annual Review of Entomology 53:409-429.

Dangerous animals–Sharks

We can all hear the ominous music, building slowly, frightfully, until the climax when Jaws attacks! Movies like Jaws have burnt this fearsome group of animals into our psyche, and I think the thought lurks somewhere in our minds whenever we visit the ocean that there are really big fish out there. There are somewhere around 440 species of shark worldwide. They are an ancient group of fish, whose overall lineage dates to before the Age of Dinosaurs. Of these hundreds of species, only 4 are known to have been involved in a significant number of fatal attacks on humans. Worldwide there is an average of 4.3 fatalities per year.

The four most dangerous species have different habits, and therefore the patterns of attacks and their danger to people are different. They are the great white shark (Carcharodon carcharias), oceanic whitetip shark (Carcharhinus longimanus), bull shark (Carcharhinus leucas), and the tiger shark (Galeocerdo cuvier).

Great White Shark

The great white, of Jaws fame, is a fearsome predator. Adult sharks are 12-17 feet in length. They are found along both coasts from Mexico into high latitude waters of Alaska, and along the east coast up to Hudson Bay. However, it is also known from deeper ocean waters, and new findings suggest that at least the west coast populations congregate in the open ocean between California and Hawaii for parts of the year. They are predators of marine mammals, turtles, large fish, and even whales. Humans are incidental targets.

During the hot summer of 1916, the Jersey Shore was the scene of a series of attacks that shuck the public, and was the inspiration for the book Jaws. Between July 1 and July 12, four people were killed. The great white is often blamed, but it could have also been a bull shark. Why there were so many attacks at that time is hard to say, and has not been repeated since.

Oceanic Whitetip Shark

The oceanic whitetip shark is actually responsible for more fatal attacks on humans than all other species combined, and it does not even frequent the coasts. It is found worldwide, and prefers warm waters and deep ocean areas. It is the unfortunate events of the twentieth century that allowed this shark to become superlative in human fatalities—it is the shark reasonable for attacks on survivors of shipwrecks and downed aircraft. During the war in the Pacific, when ships and planes were regularly shot down, many hundreds of stranded sailors were attacked and killed. Horrific stories from survivors testify to this gruesome bloodshed and led to much research by the Navy in shark repellents. Hopefully, this scale of human carnage will never occur again. And while this species is the most deadly shark, its habits make it of little concern to the average beach-goer.

Tiger shark

The tiger shark is found worldwide in mostly equatorial waters. It prefers tropical and sub-tropical warm water, and does not get into the high latitudes like the great white. It tends to stay in deep waters that line reefs, but it does occasionally move into shallow water and channels where it might encounter people. This shark is large, commonly attaining lengths of 10-14 feet, but because of its habits encounters with humans are relatively rare.

Bull shark

In contrast, the bull shark is likely the most dangerous species to humans overall. It too is common in warm waters along coasts, but it also tolerates fresh water, and can migrate into rivers. They have been found far up the Amazon River in South America, and as far north in the Mississippi River as Illinois (yikes!) (Thomerson et al. 1977). These sharks are unpredictable and are often aggressive, and because of their habit of being in shallow waters are probably responsible for the majority of near-shore attacks.

However, having said all of that, the chances of being attacked are very remote. You can see the per year compared with other animals on the chart. Was that deep, ominous music I just heard?

Average number of deaths per year caused by various animals

Thomerson, J. E., T. B. Thorson, and R. L. Hempel. 1977. The bull shark, Carcharhinus leucas, from the upper Mississippi River, near Alton, Illinois. Copeia 1977(1):166-168.

Several of the images come from sources recommended in the Nature Wallpaper post.

Dangerous animals—bears

Truth is stranger than fiction. The most recent human fatality caused by a bear took place in the wilds of Ohio. Well, sort of the wilds—just outside of Cleveland.

It seems that a young man, Brent Kandra, was tending to a captive bear when the bear attacked and killed him. The bear was owned by a man who has kept exotic animals for display in the past, and the event has sparked debate about the wisdom, and regulation, of large exotic animals being kept by private individuals (Associate Press 2010).

Whether in a cage or in the wild, bears are undeniably dangerous animals. This is the next in our series exploring dangerous animals. Unlike most of the other species we have looked at whose danger to humans is really more imagined than real, bears do come in contact with humans with some regularity, sometimes with unfortunate consequences.

In North America there are three bear species: the black bear (Ursus americanus); the brown bear (Ursus acrtos); and the polar bear (Ursus maritimus).

Black bear in the Canadian Rockies

Like so many common names, the name black bear is really not very good since the animals are often many other colors than black. The fur comes in shades of blond, black, brown, cinnamon, and gray. Interestingly, the bears tend to be black in the eastern forests, and more color variation is introduced as you survey the populations to the west, such that in California most of the bears are brown.

The black bear is the smallest of the bear species, and the most common, with the widest current distribution. They are found across Canada and south through New England into the Appalachian Mountains. There are populations in the Ozarks and in the southern states. In the west they can be found through the Pacific Northwest, and through the Rocky Mountains south into Mexico.

Black bears are generally shy and reclusive, but they can become accustom to humans, especially when they learn to associate human activity with food—through trash or handouts. In many backcountry areas where bears are common officials try to keep bears and people separate, but it is not always possible. Food storage is a great concern when camping. For example, while camping at one remote location in the Great Smoky Mountains campers were to hang their food from a cable over a stream.

Hanging a food pack over a stream in bear country

Incorrectly hanging your bag could lead to a bad time.

Results of improperly hanging your food pack

Brown bears are similarly misnamed, although the color variation is less dramatic than their black bear cousins. There are several subspecies, or races, of brown bears that you may have heard of, dividing them into coastal Kodiak and inland grizzly populations, but they are all the same species.

Brown bear

While once much more wide-spread in their distribution, brown bears are limited today to Alaska and northwest Canada, with several populations in western United States parks such as Glacier and Yellowstone.

Encounters with polar bears are understandably rare given the remoteness of their habitat. (See why polar bears are sensitive to climate change.) Polar bears spend much of their time out on sea ice, hunting seals. However, unlike other bear encounters, most encounters between humans and polar bears seem to be motivated by predation—that is, the bear is looking to eat them.

Bear encounters do sometimes lead to injury or even fatalities, and as people spend more time in bear country, the chances for an encounter naturally go up. In encounters that go badly, injury is more common than fatality as bears most often attack when they feel threatened, and once the threat is over they tend to leave. Rarely do bears prey on humans as a food source, but it does happen. In general there are about 1.8 bear-caused fatalities per year (see Clark 2003, Gunther and Hoekstra 1998, Herrero and Fleck 1990, Herrero and Higgins 1999 for discussions).

Of the dangerous animals discussed in the series, bears are the ones that most people need to be aware of, and to think about when entering the woods. Do not do stupid things in bear country, like walk around imitating the sounds of animals to attract bears (yes, it has happened), improperly store your food, try to feed the bears, get too close while taking pictures, or tease or taunt the bears. Common sense and awareness that these majestic creatures are sharing our woods will ensure that your adventures will have only the typical amount of excitement.

Associate Press. 2010. Bear who mauled caretaker is put to death in Ohio. NPR. http://www.npr.org/templates/story/story.php?storyId=129321688.

Clark, D. 2003. Polar Bear – human interactions in Canadian National Parks, 1986-2000. Ursus 14(1):65-71.

Gunther, K. A., and H. E. Hoekstra. 1998. Bear-inflicted human injuries in Yellowstone National Park, 1970-1994. Ursus 10:377-384.

Herrero, S., and S. Fleck. 1990. Injury to people inflicted by Black, Grizzly or Polar Bears: recent trends and new insights. Bears: Their Biology and Management 8:25-32.

Herrero, S., and A. Higgins. 1999. Human injuries inflicted by bears in British Columbia: 1960 – 97. Ursus 11:209-218.

Mountain Lions

They go by many names: puma, mountain lion, mountain cat, catamount, and panther, and scientifically as Puma concolor. The mountain lion is presently North America’s second largest cat, with the jaguar (Panthera onca) being the largest.

Mountain lions are widely distributed, from the Yukon Territory in Canada south through the western states, through Mexico and to the tip of South America, giving it one of the widest distributions of any species in the New World. There is a second population center in Florida, a relic population from when the species was spread coast to coast during the Ice Age. Recently, there is evidence that they are pushing their way onto the Great Plains states from the west, with reports of sightings as far east as Kansas.

They are large predators, with males weighing approximately 140 pounds, and females 90. They are considered the largest of the small cats. What?

Cats have been divided into two subfamilies, with the big cats being tigers, lions, leopards, and jaguars. The small cat subfamily includes the smaller cats like lynx and a host of species like jungle and mountain cats, marbled cat, and ocelot. The small cats also include your house cat.

Like all cats, the mountain lion is carnivorous and eats meat exclusively. They will eat anything they can catch, from insects to large animals like deer, and very occasionally elk and moose. They also are known to kill domestic livestock including cattle, horses, and sheep. It is this that caused the cats to almost be exterminated, but with legal protection their numbers are making a comeback.

The mountain lion, Puma concolor. Photograph by Bas Lammers.

This post is another in the dangerous animals series where we are exploring animals of North America that could be considered a threat to humans. However, like all the other animals, the threat is very small. Mountain lions have been known to attack and kill people, but it is a rare occurrence. Humans are increasingly moving into remote areas that host mountain lions, and encounters are increasingly likely, but mostly encounters involve seeing the tail-end of the cat disappearing.

Attacks are rare because unless they are threatened or cornered, attacks are brought about as the cat is hunting for prey, and since they are not habituated to seeing humans as prey, they avoid people. Many who are attacked are smaller in stature, such as children or women, and victims are often jogging or engaged in a similar activity that might trigger the pursuit instinct in the cat when they are very hungry.

Mountain lion foot print at a dinosaur dig in Colorado.

It is for this reason that it is recommended that if you encounter a mountain lion you should make yourself look less like prey and more like a handful. Standing up large, waving your arms, shouting, and such things will discourage the cat from attacking. Do not run.

Between 1890 and 2005 there were 88 attacks on people, and 20 fatalities (Arizona Game and Fish 2010), so on average there are a few attacks, and fewer than a single death, each year. As far as risks that we live with everyday this is really is not much of a danger.