Fighting ‘like an animal’ may not be what you expect | Science News for Students

Fighting ‘like an animal’ may not be what you expect

Evolution has produced a broad range of conflict styles
May 10, 2018 — 6:45 am EST
gemsbok fight

Extravagant headgear on male animals, such as these gemsbok in Namibia’s Etosha National Park, can give species a ferocious look. But nature’s most lethal fighters tend not to be such bulked-up adversaries.


Pick an animal.

Choose wisely. In this fantasy, you’ll transform into the creature and duel against one of your own. If you care about survival, go for the muscular, multispiked stag roaring at a rival. Never, ever pick the wingless male fig wasp. Way too dangerous!

This advice sounds exactly wrong. But that’s because many stereotypes of animal conflict get the biology backward. All-out fighting to the death is the rule only for certain specialized creatures. Whether a species is bigger than a breadbox has little to do with deadly ferocity.

Many creatures that routinely kill their own kind would be terrifying — if they were larger than a jelly bean. Certain male fig wasps unable to leave the fruit they hatch in have become textbook examples, notes Mark Briffa. He studies animal combat at Plymouth University in England. Stranded for life in one fig, these males grow “big mouthparts like a pair of scissors,” he says. They use those mouthparts to “decapitate as many other males as they possibly can.” The last he-wasp crawling has no competition to mate with all the females in his own private fruit palace.

In contrast, some of the big mammals that inspire sports-team mascots use their antlers, horns and other outsize male weaponry for posing, feinting and strength testing. Duels to the death are rare among these species.

“In the vast majority of cases, what we think of as fights are solved without any injuries at all,” says Briffa.

Evolution has produced a full rainbow of conflict styles. They range from the routine killers to animals that never touch an adversary. Working out how various species in that spectrum assess when it’s worth their while to go head-to-head has become a challenging research puzzle.

To untangle the rules of engagement, researchers are turning to animals that live large in small bodies and have no sports teams named after them. At least not yet.

Story continues below video.

Animal weaponry can look pretty scary or even deadly. But animals duel in a variety of ways that totally upend the stereotypes most people carry.
Science News/YouTube

Deadliest matches

It’s hard to imagine nematodes fighting at all. There’s little, if any, weaponry visible on their see-through, micronoodle bodies. And that includes the species called Steinernema longicaudum (STYN-er-NEE-muh Lon-jih-KAW-dum). Yet in Christine Griffin’s lab, a graduate student offered a rare hermaphrodite to a male as a possible mate. (A hermaphrodite is an individual with the traits of both a male and female.) Instead of mating, the actual male went in for the kill.

“We thought, well, poor hermaphrodite. She’s not used to mating. So maybe it’s just some kind of accident,” says Griffin. (Griffin’s lab at Maynooth University in Ireland specializes in nematodes as pest control for insects.) The grad student, Kathryn O’Callaghan, also offered females of another species to the males. The males killed some of those females too. When given a chance, males also readily killed each other. That’s how nematodes, in 2014, joined the list of kill-your-own-kind animals, Griffin says.

Killing another nematode is an accomplishment for a skinny thread of an animal with just two thin, protruding prongs. The male S. longicaudum slays by putting his mating moves to new uses.

When he encounters a female of his own species, the male coils his tail around her. He then moves the prongs — known as spicules — that are used to hold open the entrance to her reproductive tract. To kill, a male just coils his tail around another male (or a female of a different species) and squeezes extra hard. Pressure ruptures internal organs. Sometimes those spicules even punch a hole during this fatal embrace. The grip lasts from a few seconds to several minutes. Of those worms paralyzed by the attack, most are dead the next day.

nematode fight
These are Steinernema longicaudum nematodes. In a fight between the tiny worms, the male attacker (first panel) curls his body around one of his own kind and squeezes, rupturing the enemy’s internal organs (second and third panels). The victor (top, last panel) nudges the loser as if checking for any remaining resistance.
C. Griffin

Other nematodes live in labs around the world without murdering each other. So why does S. longicaudum lean toward extreme violence? Its lifestyle of making a home inside an insect inclines it to kill, Griffin suggests. An insect larva is a prize that one male worm can monopolize. It’s also the only place he can mate.

These nematodes lurk in soil without reproducing or even feeding until they find a promising target, such as the pale fat larva of a black vine weevil. Nematodes wriggle in through any opening — the larva’s mouth, its breathing pores or maybe its anus. If a male kills all male rivals inside his new home, he can start a huge family tree with lots of generations of offspring. Those offspring might total in the hundreds of thousands, Griffin points out.

Territorial female slayers

Ficus citrifolia
Dramatic fights rage inside green, flower-filled sacs on this tree (Ficus citrifolia) that will eventually mature into figs. Certain male fig wasps are famous for their lethal brawls. However, research shows females also go at it.
C. Jandér

A defendable bonanza like a weevil larva, or a fig, has become a theme in the evolution of deadly fighting. Biologists have studied violence in certain male fig wasps for decades. However, more recent research has revealed that some females kill each other, too.

A female Pegoscapus (Pay-go-SKAY-pus) wasp is a bit longer than a poppy seed. When she chooses one particular pea-sized sac of flowers — a fig-to-be — she’s deciding her destiny. That sac is most likely her only chance at laying eggs. And it will probably be the fruit she will die in, notes Charlotte Jandér. She’s an evolutionary ecologist at Harvard University in Cambridge, Mass.

female wasps
Inside a fig, two females grapple jaw-to-jaw beside a wasp that may have died in earlier combat.
C. Jandér

Shortleaf fig trees have “a delicate flowery smell,” Jandér says. The blooms, though, are hidden inside little green-skinned sacs. To reach these inner riches and lay one egg per flower in as many flowers as she can, the wasp must push through a tight tunnel. The squeeze can take roughly half an hour. And it could rip her wings and antennae. Reaching the inner cavity carpeted in whitish flowers, “there is plenty of space for one wasp to move around,” Jandér says. But more than one gets cramped, and conflicts get desperate.

In a wasp species from Panama that Jandér has watched, females “can lock on to each other’s jaws for hours and push back and forth,” she says. In a Brazilian species, 31 females were found decapitated among 84 wasps. Jandér was part of a research team that reported this in 2015. It was the first documented female-to-female killing in fig wasps.

Walk away

Many animal species have ways to back off rather than fight to the death. Briffa studies one example: sea anemones. And yes, anemones fight.

The formal name for beadlet sea anemones is Actinia equine (Ak-TIN-ee-uh E-KWY-nuh). They release their sperm and eggs into open seawater. The animals don’t need to argue over mates. For a prime bit of tide-pool rock, however, tensions may rise.

anemone fighting tentacles
When not battling, an anemone’s fighting equipment (which can sometimes be colored blue) is pulled in.
S. Lane

Below a beadlet’s pinkish, swaying food-catcher tentacles are what often look like “little blue beads,” Briffa points out. These are fighting tentacles, or acrorhagi (AA-kroh-RAJ-ee). When combat looms, the anemone inflates them. “Imagine someone pulling out their bottom lip to make a funny face,” he says.

It’s no joke for an impertinent neighbor. Anemones are distant relatives of stinging jellies. And their acrorhagi carry harpoon-shooting, toxin-injecting capsules. Combatants rake stinger acrorhagi down each other’s soft flesh. “It almost looks like they’re punching each other,” Briffa says. “When one of the anemones decides it’s had enough and wants to quit the contest, it actually actively walks away.”

“Walk” is used loosely here, notes Sarah Lane. Then she demonstrates by alternately arching her hand and flattening it in a measured trip across the Skype screen. She’s a postdoc in Briffa’s lab. Maybe it moves “like a cartoon caterpillar?” she says, trying to describe the gait. Or perhaps “a concertina?”

To start fights, the researchers place anenomes side by side in the lab. About one time in every three the anemones concertina away or otherwise resolve the tension without any acrorhagi swipes. Backing down this way makes sense considering that a full exchange “looks quite vicious,” Lane says. Strikes leave behind bluish fragments of acrorhagi full of stinging capsules. Those capsules kill tissue on the recipient.

achrorhagi damged
Sea anemones escalate some battles and “walk away” from others. After a fight, an anemone’s stinging tentacles, which are called acrorhagi, show holes after losing tissue to an opponent.
S. Lane

The attacker won’t leave unscathed either. Close-ups show open wounds where acrorhagi tissue was pulled out. An anemone “literally can’t hurt an opponent without ripping parts of itself off,” she explains.

Injuries to an attacker from swiping, biting or other acts of aggression get overlooked in discussing how animals weigh the costs and benefits of dueling. Lane and Briffa argued this in the April 2017 Animal Behaviour. The sea anemones may be an extreme example of self-harm from a strike. Still, they’re not the only one.

Humans can hurt themselves when they attack. Deciding whether to fight can have some unintended impacts, Lane points out. In a bare-handed punch at somebody’s head, little bones in the hand crack — creating so-called boxer’s fractures — before the skull cracks. With the introduction of gloves around 1897, boxer’s fractures basically disappeared from match records, Lane says. Before gloves, however, records show no reported deaths in professional matches. Once gloves lessened the costs of delivering high-impact punches, deaths began appearing in the records.

Worth the fight?

Sea anemones don’t have a brain or central nervous system. However, costs and benefits of fighting somehow still matter. The animals clearly pick their fights. They escalate some blobby sting matches and creep away from others.

Just how anemones choose — or how any animal chooses — when to fight and when to back down turns out to be a rich vein for research. Scientists have proposed versions of two basic approaches. One is called mutual assessment. This “is sussing out when you’re weaker and giving up as soon as you know,” Briffa says. “That’s the smart way.” Yet the evidence Briffa has so far, he says with perhaps a touch of wistfulness, suggests anemones use “the dumb way of giving up.”

This “dumb” option is called self-assessment. Animals resort to this when they can’t compare their opponent’s odds of winning with their own. Maybe they fight in shadowy, murky places. Maybe they don’t have the neural “smarts” for that type of comparison. For whatever reason, they’re stuck with “keep going until you can’t keep going anymore,” he says. Never mind if the fight is hopeless from the beginning.

The odds of fighting “smart” look better for the animals that Patrick Green of Duke University in Durham, N.C., studies. These creatures have a brainlike ganglion (GANG-lee-un). And they come close to fighting with superpowers. He’s working with, of course, mantis shrimp.

The high-powered smashers among these small crustaceans flick out a club to move at “highway speeds,” Green says. What’s more remarkable is that the club reaches those speeds really fast. They accelerate like a bullet shooting out of a .22 caliber pistol.

When the clubs wham a tasty snail, the bounce back creates a low-pressure zone that vaporizes water. “I always feel weird saying this because it seems just goofy.” Still, Green says, “that does release heat equivalent to the surface of the sun.” Fortunatey, it lasts only a fraction of a microsecond.

When smasher mantis shrimp — males or females — fight each other, they batter rivals into oblivion. The reality, though, is arguably stranger. They superpunch each other. But the blows land on an area that can withstand the force. It’s the telson. This bumpy shield covers the rump.

In Caribbean rock mantis shrimp, the battle is often over after just one to five blows. Those blows happen too fast for the human eye to see. In test fights between animals of equal size, the winner is not the animal that lands the most forceful blow. Instead, it’s the one that gets in the most punches. Then, with no visible gore, one dueler just gives up.

Story continues below image.

rock mantis shrimp fight
Power-punching Caribbean rock mantis shrimp can settle disputes without deadly blows. Here, the combatant at right lifts its telson, or rump shield, which takes the hits.
Roy Caldwell

Green and Sheila Patek, also at Duke, propose that this telson sparring permits genuine mutual assessment. That’s the smart way of losing a fight. It’s difficult to figure out what lurks in the neural circuits of an arthropod. However, the researchers presented multiple lines of evidence in the January 31 Proceedings of the Royal Society B.

One strong clue came from matches that Green staged between mantis shrimp of different sizes. He didn’t see a trend of smaller ones pointlessly pounding telsons as the lightweights fought bigger animals. Those bigger animals were going to win anyway. And it seemed as if the smaller ones understood that. This suggests something more than self-assessment is going on, Green and Patek now propose.

Researchers think they have seen mutual assessment in other animals too. These include wrestling male New Zealand giraffe weevils. They’ve also seen it in male jumping spiders that flip up banded legs in “Goal!” position to intimidate rivals. Analyzing assessment gets tricky.

For instance, scientists, dazzled by the sights and sounds that our own sensory world emphasizes, may be underestimating chemical cues. Among crawfish, “part of their fight is squirting urine in one another’s faces,” Briffa says.

Paradoxically peaceful

rhinoceros beetle
Rhinoceros beetles have elaborate horns that the males use in duels over potential mates.
Frantisek Bacovsky

Many of the scariest-looking weapons end up causing little bodily harm. Some are specialized for combat that’s more strategic than gory. Other weapons look so scary they hardly ever get used.

Erin McCulloughan is an evolutionary biologist, now working at the University of Western Australia in Perth. The male Asian rhinoceros beetles that she studies host odd horns. The forked horns on their heads stretch nearly two-thirds the beetle’s body length. Surprisingly lightweight, the horns look cumbersome. They resemble “a Styrofoam leg sticking out of your forehead,” she says.

She watched the guys compete furiously with each one night at a university in Taiwan. Despite it being hot and muggy, her shirts had the collars pulled way up. Leather gloves covered her hands. She hardly blended in with the students. So why all this gear? “You shouldn’t wear mosquito repellant when you’re working with insects,” she explains.

But it was worth it. The scene illuminated by her head lamp was “really messy and chaotic,” she recalls. Beetles flying out of the dark fought to dominate cracks in ash tree bark that oozed sap and attracted females. A dominant beetle would grip the bark and use his horn to flick incoming challengers off the branch left and right — until some other guy unseated him. Getting thrown off the limb doesn’t kill losers. Often they buzz right back for another try.

Yet from the vantage point of evolution, a male who doesn’t mate might as well be dead. His genes will never be carried on to the next generation. That meant his winning a female has important impacts for his community impacts. Males with longer horns are better at flicking off other males. Yet longer horns also are more likely to snap, McCullough notes. And a broken horn won’t grow back.

beetle graph
The largest male rhinoceros beetles grow the longest horns, which gives those males an advantage in monopolizing a mate.
I.A. Warren et al/PLOS ONE 2014

The extravagant tool needs to be a pry bar of just the right length, lightness and strength. Fresh, new horns on male beetles just starting their fighting careers have about four times the strength the horns need to resist cracking. (That’s about the safety factor that engineers build into bridges but less than the standard for elevator cables, she notes.)

Horns or antlers on male mammals often can kill. Yet fatal fights may be rare, says Douglas Emlen. He’s a biologist at the University of Montana in Missoula. One of his favorite studies comes from decades-old research on caribou. That study looked at about 1,308 sparring matches between male caribou in Alaska. With all this glaring, snorting and rushing, only six matches escalated into violent, bloody fights.

Evolution usually does not favor extremes in teeth, horns or other such body weaponry. Certain forms of rivalry for mates, however, can foster certain weapons to expand extravagantly in a body-part arms race. There are common patterns to such arms races, Emlen says, including some cheating.

Among conditions that favor an arms race are rivalries playing out in one-on-one duels, he says. Imagine a magnificently endowed dung beetle in a tunnel. He guards a female in the depths behind him. One by one, he must fend off all rivals for her attention. Growing bigger and bigger horns, however, comes with a cost. Eventually, only an animal with the best nutrition, genes and luck can spare the resources to grow a truly commanding horn. And at this point, horn size signals a male that can overpower just about all rivals. Only another supermale will engage him in an all out fight. The rest of the time, his threatening weaponry keeps the peace with barely a bump or a bruise.

Yet this is “a very unstable situation,” Emlen adds. “It creates incentives for males to cheat.” Or maybe the word should be “innovate.” He has found that big-horned male dung beetles defending their tunnels can be outmaneuvered by small rivals. Those smaller beetles dug bypass tunnels around the guard zone. That let them mate with the supposedly defended female.

At the far extreme of animal rivalries are some species that blur the meaning of fights. Some butterflies, such as the speckled wood butterfly, “fight” without physical contact. Males compete for a little sunlit dapple on the forest floor by flying furious circles around each other until one gives up and scrams. No gore, but probably really exhausting.

Power Words

(more about Power Words)

acrorhagus     (plural: acrorhagi) A type of specialized inner tentacle on sea anemones that can be used defensively to ward off encroachment by a competitor. The defending anemone’s acrorhagi shove barbed poison-injecting capsules into the tissue of its adversary — until that adversary moves away.

anus     The opening at the end of an animal's digestive system through which solid waste leaves the body.

arthropod     Any of numerous invertebrate animals of the phylum Arthropoda, including the insects, crustaceans, arachnids and myriapods, that are characterized by an exoskeleton made of a hard material called chitin and a segmented body to which jointed appendages are attached in pairs.

beetle     An order of insects known as Coleoptera, containing at least 350,000 different species. Adults tend to have hard and/or horn-like “forewings” which covers the wings used for flight.

biology    The study of living things. The scientists who study them are known as biologists.

Caribbean     The name of a sea that runs from the Atlantic Ocean in the East to Mexico and Central American nations in the West, and from the southern coasts of Cuba, the Dominican Republic and Puerto Rico down to the northern coasts of Venezuela and Brazil. The term is also used to refer to the culture of nations that border on or are islands in the sea.

caribou     Antler-wielding North American deer belonging to the species Rangifer tarandus. They are the same species as the European reindeer, although the two groups show enough subtle differences to be considered subspecies. Caribou tend to be a bit bigger and their fur is not as thick or dense as a reindeer’s.

caterpillar     The larval stage of moths and butterflies. Somewhat wormy-shaped crawlers, caterpillars tend to eat leaves and other plant bits. Some will, however, dine on other insects.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

circuit     A network that transmits electrical signals. In the body, nerve cells create circuits that relay electrical signals to the brain. In electronics, wires typically route those signals to activate some mechanical, computational or other function.

colleague     Someone who works with another; a co-worker or team member.

crustaceans     Hard-shelled water-dwelling animals including lobsters, crabs and shrimp.

dung beetle     A type of insect found on all continents except for Antarctica. They feed on a soupy liquid that they extract from animal feces (or dung). Able to fly long distances, these beetles use specialized antennae to sniff out the dung and home in on this food source, 

ecology      A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

egg     The unfertilized reproductive cell made by females.

engineer     A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.

evolution     (v. to evolve) A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the particular conditions in which it developed. Or the term can refer to changes that occur as some natural progression within the non-living world (such as computer chips evolving to smaller devices which operate at an ever faster speed).

evolutionary biologist     Someone who studies the adaptive processes that have led to the diversity of life on Earth. These scientists can study many different subjects, including the microbiology and genetics of living organisms, how species change to adapt, and the fossil record (to assess how various ancient species are related to each other and to modern-day relatives).

evolutionary ecologist     Someone who studies the adaptive processes that have led to the diversity of ecosystems on Earth. These scientists can study many different subjects, including the microbiology and genetics of living organisms, how species that share the same community adapt to changing conditions over time, and the fossil record (to assess how various ancient communities of species might be related to each other and to modern-day relatives).

factor     Something that plays a role in a particular condition or event; a contributor.

force     Some outside influence that can change the motion of a body, hold bodies close to one another, or produce motion or stress in a stationary body.

fracture     (noun) A break. (verb) To break something and induce cracks or a splitting apart of something.

gait     The pattern of leg motions by which an animal walks from place to place.

ganglion       A sac-like cyst (called a ganglion cyst) formed made of tissue that lines a joint or tendon. Or a collection of nerve cell that cluster together at some site outside the brain.

gene     (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

generation     A group of individuals (in any species) born at about the same time or that are regarded as a single group. Your parents belong to one generation of your family, for example, and your grandparents to another. Similarly, you and everyone within a few years of your age across the planet are referred to as belonging to a particular generation of humans. The term also is sometimes extended to year classes of other animals or to types of inanimate objects (such as electronics or automobiles).

graduate student     Someone working toward an advanced degree by taking classes and performing research. This work is done after the student has already graduated from college (usually with a four-year degree).

harpoon     A spear-like weapon that is thrown to pierce an aquatic animal. It’s barbed or hooked head keeps the weapon attached to the animal. An attached rope can then be pulled in, bringing the animal to a hunter’s boat. A harpoon may also be any latching device that pierces a surface to hold onto it.

innovation     (v. to innovate; adj. innovative) An adaptation or improvement to an existing idea, process or product that is new, clever, more effective or more practical.

insect     A type of arthropod that as an adult will have six segmented legs and three body parts: a head, thorax and abdomen. There are hundreds of thousands of insects, which include bees, beetles, flies and moths.

intimidate     To frighten by force or threats. Or to make timid (which is the root of this word) through such actions.

jellies     (in biology) These are gelatinous animals that drift in water (mostly seawater) or brackish (semi-salty) estuaries. For more than 500 million years, they have moved around the oceans by pumping pulses of water through their jelly-like tissue. Their body often has an umbrella-shaped bell. Trailing from around a central mouth may be many tentacles. Although jellies don’t have brains, they do have a nervous system which can sometimes detect light, movement or certain chemicals. Some members of this family, known as cnidarians, are known as jellyfish. In fact, none are true fish but related to hydras and corals.

larva     (plural: larvae) An immature life stage of an insect, which often has a distinctly different form as an adult. (Sometimes used to describe such a stage in the development of fish, frogs and other animals.)

limb     (in physiology) An arm or leg. (in botany) A large structural part of a tree that branches out from the trunk.

literally     A term that the phrase that it modifies is precisely true. For instance, to say: "It's so cold that I'm literally dying," means that this person actually expects to soon be dead, the result of getting too cold.

mammal     A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.

mantis shrimp     A marine animal related to crabs and lobsters. Mantis shrimp use armlike body parts to kill prey. They are often multicolored and have a very complex vision system.

model     A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.

nematode     A type of roundworm, usually found in soil, that also can live within other creatures as a parasite. It is usually quite small, with no eyes, ears or nose. However, the occasional species can grow up to a meter long.

nervous system     The network of nerve cells and fibers that transmits signals between parts of the body.

New Zealand     An island nation in the southwest Pacific Ocean, roughly 1,500 kilometers (some 900 miles) east of Australia. Its “mainland” — consisting of a North and South Island — is quite volcanically active. In addition, the country includes many far smaller offshore islands.

nutrition     (adj. nutritious) The healthful components (nutrients) in the diet — such as proteins, fats, vitamins and minerals — that the body uses to grow and to fuel its processes. A scientist who works in this field is known as a nutritionist.

organ     (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.

physical     (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).

pore     A tiny hole in a surface. On the skin, substances such as oil, water and sweat pass through these openings.

post-doc     Short for postdoctoral scholar. It’s a     research position for people who have just completed their doctorate (PhD) in some field of study. It allows the individual to acquire new skills or pursue new lines of research on the road to a research career.

pressure     Force applied uniformly over a surface, measured as force per unit of area.

range     The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists. (in math or for measurements) The extent to which variation in values is possible. Also, the distance within which something can be reached or perceived.

sea anemone     An animal that usually lives on the seafloor and reefs. Although the young larvae disperse through the water, they eventually settle and permanently anchor themselves to a solid structure. They have a tube like structure and resemble a soft, flower. But what appear to be petals are actually stinging tentacles that ring their mouths.

seawater     The salty water found in oceans.

self-harm     Intentionally injuring one’s body. Examples may include cutting, scratching or burning oneself. This unhealthy behavior is typically a way this individual attempts to cope with emotional pain. It’s usually not intended as a suicide attempt. Also known as self-injury.

skull     The skeleton of a person’s or animal’s head.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

spectrum     (plural: spectra) A range of related things that appear in some order. (in light and energy) The range of electromagnetic radiation types; they span from gamma rays to X rays, ultraviolet light, visible light, infrared energy, microwaves and radio waves.

sperm     The reproductive cell produced by a male animal (or, in plants, produced by male organs). When one joins with an egg, the sperm cell initiates fertilization. This is the first step in creating a new organism.

spicule     A small and usually slender, sharp-pointed crystal or part of some object.

spider     A type of arthropod with four pairs of legs that usually spin threads of silk that they can use to create webs or other structures.

stereotype     A widely held view or explanation for something, which often may be wrong because it has been overly simplified.

Styrofoam     A trademarked name for a type of rigid foam made from light-weight polystyrene plastic. It is used for everything from home craft projects to decorative ornaments and building insulation.

telson      The last segment in the abdomen of some segmented worms or some arthropods — such as insects, crustaceans or spiders, for instance.

territorial     (in biology) An adjective for organisms that try to keep others of their species away from an area they control.

tissue     Made of cells, it is any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.

tool     An object that a person or other animal makes or obtains and then uses to carry out some purpose such as reaching food, defending itself or grooming.

toxin     A poison produced by living organisms, such as germs, bees, spiders, poison ivy and snakes.

tract     A particular, well-defined area. It can be a patch of land, such as the area on which a house is located. Or it can be a bit of real estate in the body. For instance, important parts of an animal’s body will include its respiratory tract (lungs and airways), reproductive tract (gonads and hormone systems important to reproduction) and gastro-intestinal tract (the stomach and intestines — or organs responsible for moving food, digesting it, absorbing it and eliminating wastes).

trait     A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.

vaporize     To convert from a liquid to a gas (or vapor) through the application of heat.

vein     Part of the body’s circulation system, these tubes usually carrying blood toward the heart.

weevil     Small beetles that belong to the Curculionidae family. There may be at least 60,000 different species. They tend to have a snout-like head part that allows them to penetrate seeds, nuts and plant stems.


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  • HS-LS2-8


Journal:​​ ​P.A. Green and S.N. Patek. Mutual assessment during ritualized fighting in mantis shrimp (Stomatopda)Proceedings of the Royal Society B. Vol. 285, January 31, 2018, 20172542. doi: 10.1098/rspb.2017.2542.

Journal:​​ ​S.M. Lane and M. Briffa. The price of attack: rethinking damage costs in animal contestsAnimal Behaviour. Vol. 126, April 2017, p. 23. doi: 10.1016/j.anbehav.2017.01.015.

Journal:​​ ​D.W. Dunn et al. Mortal combat and competition for oviposition sites in female pollinating fig waspsBehavioral Ecology. Vol. 26, January 1, 2015, p. 262. doi:10.1093/beheco/aru191.

Journal:​​ ​K.M. O’Callaghan et al. Interference competition on entomopathogenic nematodes: male Steinernema kill members of their own and other speciesInternational Journal for Parasitology.Vol. 44, November 2014, p. 1009. doi. 10.1016/j.ijpara.2014.07.004.

Journal:​​ ​E.L. McCullough. Mechanical limits to maximum weapon size in a giant rhinoceros beetleProceedings of the Royal Society B. Vol. 281, July 7 2014, 20140696.  doi: 10.1098/rspb.2014.0696.