Cannibalism

by Bill Schutt

  Additionally, a 2013 study by Japanese researchers showed that snails skewered by love darts delayed re-mating with other individuals, an indication that something in the dart’s mucous coating suppressed subsequent mating behavior—thus reducing the possibility that another male’s sperm would outcompete the dart shooter’s.

  According to Chase, “It’s all basically sexual selection.” In other words, in any given population, some individuals outproduce other individuals because they’re better at securing mates, usually by making themselves more attractive to the opposite sex or by beating back the competition. In land snails, explanations for who got the edge and how they achieved it are confounded by the fact that mating individuals not only exchange sperm with each other, but explosive projectiles as well.

  Before leaving the topic of snails, if all this talk about love darts has you thinking about one of our most endearing holiday characters, you aren’t alone. Ronald Chase believes that Cupid, the Roman version of the Ancient Greek god Eros, had his origin in land snails and their love darts.

  “I think that the Cupid myth arose from Ancient Greeks observing snails mating and shooting love darts,” Chase explained. “The species that we worked on in our experiments is found in Greece and I’m sure they shoot love darts over there as well.” Ever the scientist, Chase added that there was no hard evidence yet and that neither he nor his students was able to find images of snails shooting love darts on Ancient Greek coins or pottery. Personally, I’ve always been a bit creeped out by the idea of a nude, weapon-wielding infant with wings, but considering that the Greeks could have equipped him with turret eyes and a slime trail, I’m willing to cut the current incarnation some slack.

  4: Quit Crowding Me

  Hunger has its own logic.

  — Bertolt Brecht

  Overcrowded conditions often coincide with another of Gary Polis’s cannibalism-related generalizations, namely that incidents of cannibalism increase with hunger and with a decrease in the availability of alternative forms of nutrition, a point that will become horribly clear once we begin our investigation of human cannibalism.

  Carrying the banner (albeit a tiny one) for crowd-related cannibalism are the Mormon crickets (Anabrus simplex). These insects are native to the North American West and belong to the order Orthoptera, which contains grasshoppers, crickets, and locusts. The fact that A. simplex is actually a form of jumbo katydid also makes them members of an unofficial assemblage composed of misnamed animals like “flying foxes” (which aren’t foxes) and “tree shrews” (guess).9 Attaining a body length of nearly three inches, Mormon crickets are flightless, but like their winged cousins, the grasshoppers and locusts, they’re renowned for their spectacular swarming behavior and mass migrations. According to biologist and Mormon cricket expert Stephen Simpson, favorable early spring conditions like warm weather and moisture can lead to the nearly simultaneous hatching of several million individuals. Almost immediately, the nymphs begin to march, and they do so in a spectacularly well-coordinated manner.

  I asked Simpson why Mormon crickets participated in such large-scale movements. He cited studies showing that individuals separated from their swarm suffered 50 to 60 percent mortality from predators. “They got eaten by birds, rodents, and spiders if separated but were safe from predation in a crowd.”

  Seeking to illuminate principles of mass migration and collective behavior, Simpson and his coworkers conducted food preference tests on captive Mormon crickets. They determined that protein and salt were the limiting resources being sought by the swarming insect masses. Incidents of cannibalism began soon after these resources were depleted, since the nearest source of protein and salt becomes a neighboring cricket. According to Simpson, “Each insect chases the one in front, and in turn is chased by the cricket behind.” Stopping to eat becomes a dangerous behavior, the biologist explained, requiring individuals to fend off other members of the swarm with their powerful hind legs. “Losing a leg is fatal,” he told me. “The weak and the injured are most at risk.”

  Simpson demonstrated this experimentally by gluing tiny weights to some of the crickets, thus causing them to lag behind their unencumbered swarm-mates. Almost immediately, the miniature Jacob Marleys were attacked and eaten by the hungry horde approaching from behind.

  In the end, Simpson and his colleagues determined that the massive migratory bands were actually forced marches, demonstrating “coherent mass movement at the level of a huge marching band.” Here, though, band members that can’t handle the pace run a serious risk of being eaten.

  While avian cannibalism might be relatively rare in the wild, all bets are off once birds are removed from their natural setting, and packed shoulder-to-shoulder (or ruffled feather to ruffled feather). When thousands of stressed-out birds have little to occupy their time, the situation can deteriorate rapidly. In these instances the real meaning of the term “pecking order” becomes gruesomely apparent as some individuals are pecked to death and eaten. Initially, cannibalism on poultry farms was thought to result from a protein deficient diet, but researchers now believe that it’s actually misdirected foraging behavior related to cramped and inadequate housing conditions.

  As the poultry and egg industries became established, feather pecking and cannibalism (known in the trade as “pick out”) became two of the most serious threats faced by poultry farmers. To stop cannibalism and prevent the loss of their valuable egg-laying hens, farmers routinely clipped off the tip of the bird’s beak, a reportedly painful process. In the 1940s, however, the National Band and Tag Company came up with a far more painless and fashion conscious method to deal with the problem of cannibalistic chickens. Their design team reasoned that if the birds couldn’t see “raw flesh or blood” then they wouldn’t cannibalize each other and so they came up with “Anti-pix”—mini sunglasses equipped with red celluloid lenses and aluminum frames. Purchased in bulk ($27 for 1,000) and attached to the upper portion of the bird’s beak near the base, poultry farmers were informed that having their chickens see the world through rose-tinted glasses would “make a sissy of your toughest birds,” and apparently they worked.10

  Currently, only 75 species of mammals (out of roughly 5,700) are reported to regularly practice some form of cannibalism. Although this number will likely increase as more researchers become interested in the topic, the overall low occurrence of cannibalism in mammals is likely related to relatively low numbers of offspring coupled with a high degree of parental care (compared to non-mammals).

  The golden hamster (Mesocricetus auratus), also known as the Syrian hamster, is a popular pet for children, but these cuddly fuzz balls are also known to display some nightmare-inducing behavior in captivity. The problems stem from major differences between their natural habitats and the captive conditions under which they are typically held. Native to northern Syria and Southern Turkey, M. auratus lives in dry desert environments. Adults are solitary, highly territorial, and widely dispersed. Individuals inhabit their own burrows and emerge for short periods at dawn and dusk to feed and mate. This crepuscular lifestyle is thought to help them avoid nocturnal predators like owls, foxes, and feral dogs. The results of a study on golden hamsters in the wild emphasized the major differences between natural conditions and those imposed on pet hamsters. For example, the researchers determined that in the wild, the average time hamsters spent on the surface during a 24-hour period was 87 minutes.

  The problems between natural and captive conditions often begin in pet shops, where male and female golden hamsters are often kept in unnaturally large groups and displayed in well-lit aquaria. They are purchased singly (preferable) or in pairs (males and females if the store personnel know how to differentiate sexes). As pets, these desert-dwellers are housed in cages or trendy modular contraptions where translucent plastic tubes link “rooms” to each other. Unfortunately, the cages are often too small and golden hamsters have a hard time fitting through the plastic tubes, especially when pregnant or obese from overfeed
ing. Cage floors are usually covered in cedar shavings, which are pleasant enough to the human nose but hardly reminiscent of a desert environment. Regularly handled by children and often subjected to excessive noise and damp conditions (resulting from soiled cage bedding or leaky water bottles), many pet hamsters spend their existence under the watchful gaze of dogs and cats, their owners blissfully unaware that these are the hamster’s natural enemies.

  As a result of this laundry list of captivity-related stresses, female golden hamsters, especially younger ones, frequently cannibalize their own pups. Beyond diet (too much or too little food) and housing conditions, cannibalism can be triggered if hamsters are handled late in their pregnancy or if the babies are handled within ten days of their birth. The presence of additional individuals (even fathers) can also lead females to consume their own pups and heterocannibalism can occur if adult females encounter unrelated young. Pet experts suggest that filial cannibalism can be prevented by isolating pregnant individuals, making sure that water and nutritional requirements are met, and refraining from handling female hamsters before and after they give birth. Finally, pet owners should not handle newborns of any species unless they are prepared to nurse the animals themselves.

  Cannibalism of adults can also take place when several mature golden hamsters are kept in the same cage, and this includes siblings, who reach sexual maturity at around four weeks of age. Under these conditions, fighting is common, and serious injuries or even fatalities can result. In the latter instances, the survivor of the battle typically consumes the carcass of the loser.

  Although mice, rats, guinea pigs, and rabbits also occasionally cannibalize their young in captivity (primarily when food and water are scarce), there are several factors that appear to make golden hamsters even more prone to this type of behavior. Most significant is the fact that M. auratus has the shortest gestation period (16 days) of any placental mammal, and they can become pregnant again within a few days of giving birth. This means that females, already weakened and stressed out by the rigors of pregnancy, birth, and nursing, may be tending a new brood of eight to ten pups less than three weeks after their previous delivery.

  When non-human primates (i.e., monkeys and apes) are compared to other mammal groups, cannibalism is rare, having been observed in only 11 of 418 extant species. Many examples of primate infanticide and/or cannibalism were thought to be stress-related and, generally, this turned out to be true. Overcrowding, unnatural circumstances (like the transfer of a troupe of rhesus monkeys to a new island), and deficient captive conditions play a role in most of these reports, with the latter blamed for incidents of infanticide in bush babies, lemurs, marmosets, and squirrel monkeys. In each case, the victims were invariably neonates, while the aggressors were either group members or relatives, including siblings. Responding to the problem, caretakers at facilities housing breeding primate colonies began isolating pregnant females before they gave birth, and these efforts have proven effective.

  One primate group in which infanticide and cannibalism are relatively common practices is the chimpanzees (Pan troglodytes), and descriptions of the behavior among our closest relatives are both chilling and fascinating.

  Initially, reports of chimpanzee cannibalism focused solely on adult males, who routinely killed and sometimes consumed infants belonging to “strangers” (i.e., adult females from outside their own groups). According to Dr. Jane Goodall, female chimpanzees sometimes transferred from one community to another. “A female who loses her infant during an encounter with neighboring males is likely to come into oestrus within a month or so and would then, theoretically, be available for recruitment into the community of the aggressors.” Similar behavior is seen in bears and large cat species, like lions.

  Other attacks by male chimps on infant-bearing females took place during “inter-community aggression” as occurs, for example, when groups of male chimpanzees patrolling the outer edges of their territories encountered individuals from adjacent communities.

  Then, in 1976, Goodall reported on three observations in which two female chimps were involved in within-group infanticide and cannibalism in Tanzania’s Gombe National Park. What made these attacks unique was the absence of male involvement. Stranger yet was the fact that the individuals involved were a mother (Passion) and daughter (Pom), whose seemingly premeditated tag-team approach to somewhere between five and ten infant-bearing females provided researchers with a grim explanation for previously unexplained infant disappearances. Goodall believes that the attacks on the mothers functioned solely as a means to acquire food, since “once they had established their claim over their prey they made no further aggressive attacks on the mothers.”

  Thirty years later, similar attacks were carried out by female chimp coalitions against infant-bearing mothers in in Uganda’s Budongo Forest. A team led by comparative psychologist Simon Townsend believes that the lethal attacks were triggered by an influx of females, leading to increased competition for resources.

  Although acts of cannibalism in chimpanzees are not everyday occurrences, some researchers have suggested that the encroachment of humans into the areas surrounding preserves inhabited by chimps will eventually lead to population density issues and more competition for dwindling resources. If this occurs, incidences of cannibalism by our closest relatives may be expected to increase.

  * * *

  9 Biological nomenclature is full of misleading scientific names. Vampyressa, Vampyrodes, Vampyrops and Vampyrum are all bat genera, but none of them feed on blood. There are also bad puns, like Apopyllus now (a sac spider) and Ittibittium (a tiny mollusk), as well as rude sounding names, like Pinus rigida (the pitch pine) and Enema pan (a scarab beetle).

  10 Although Anti-pix specks are now collector’s items, the idea behind them lives on in plastic clips called “Peepers,” which can be attached via a pin through the nostrils of various commercially raised game birds. For an extremely entertaining short on the original Anti-pix specks, check out the following link: http://www.nationalband.com/Chickenglasses.mov

  5: Bear Down

  In Panama, I found a spider that eats it own limbs during lean times. I am told they grow back. But though the distinction is razor-thin, desperation is not the same thing as determination.

  — Taona Dumisani Chiveneko, The Hangman’s Replacement: Sprout of Disruption, 2013

  If you believe the news reports, this is not a good time to be a polar bear. Over the past several years, there have been dozens of headlines that ran something like this: “Polar Bears Are Turning to Cannibalism as Arctic Ice Disappears,” “Is Global Warming Driving Polar Bears to Cannibalism?” “Polar Bear Cannibalism Linked to Climate Change.”

  As a vertebrate zoologist, I was interested in determining whether or not a transition in polar bear diets had actually taken place. And if it had, I wondered whether we were involved.

  Polar bears (Ursus maritimus, Latin for “marine bear”) are among the world’s largest carnivores, a diverse mammalian order whose members include cats (felids), dogs (canids), raccoons (procyonids), and weasels and their relatives (mustelids). They are, of course, famous for their meat-eating diets and many of them share a characteristic known as carnassial teeth (or carnassials). In the majority of mammal species, when the jaw closes, the premolar and molar teeth on the upper jaw fit snugly into those on the lower jaw. This facilitates the crushing of food items before they’re swallowed. In most carnivore species, though, when the jaws close, the last upper premolar and the first lower molar on each side shear past each other like blades, effectively slicing large pieces of meat into smaller pieces that can be readily swallowed. Carnassial dentition was lost in most bears as they evolved more omnivorous feeding habits. Here, the hard-to-digest plant material required a mash-up by more traditional molars, thus increasing its surface area and allowing for more efficient breakdown by enzymes like cellulase. In polar bears, however, fully functional carnassials have apparently re-evolved—a reflection of the species’ st
rict meat-eating diet, which consists primarily of ringed seals (Pusa hispida) and bearded seals (Erignathus barbatus).

  Secondarily evolved traits like carnassial teeth in polar bears are common in nature. For example, having inherited the ability to swim from their fishy ancestors, many ancient vertebrates lost the ability (and related features like fins) as they became more and more adapted to terrestrial lifestyles. Swimming re-evolved in some lineages, leading to creatures like seals and whales, whose fins are actually modified terrestrial limbs.

  Cannibalism has been recorded in at least 14 species of carnivores. In pumas (Puma concolor), lynx (Lynx lynx), leopards (Panthera pardus), and sea lions (Phocarctos hookeri), it appears to occur for many of the usual reasons, including stress (due to lack of food), elimination of rivals, and increased mating opportunities.

  Heterocannibalism, in this case, eating the cubs that another male sired, is clearly a reproductive strategy in male lions (Panthera leo) after taking over a pride. Through the practice of infanticide, the incoming males terminate the maternal investment in unrelated cubs. A lioness with cubs will not come into heat for a year and a half after giving birth, but similar to what has been observed in other mammals, a lioness that loses her cubs becomes sexually receptive almost immediately.