The Spiders That Would Be Ants

Imposters abound in the animal kingdom.
Imposters: imposterの複数形。(他人を詐称する)詐欺師、 ぺてん師
abound: たくさんいる、富む

Peruse any textbook description of mimicry-in which one species evolves to resemble another-and you will encounter various classic examples, such as the king snake, which copies the coral snake, or the hoverfly, which masquerades as a bee.
mimicry: まね、ものまね、模造品、擬態
hoverfly: ハナアブ、アブバエ、ショクガバエ
masquerades: masqueradeの三人称単数現在。masqueradeの複数形。見せかけ、 虚構

Less familiar, but in many ways even more fascinating, are the mimics in a genus of jumping spider known as Myrmarachne, which look for all the world like ants.

Unlike other jumping spiders, with their furry, round bodies, Myrmarachne species have smooth, elongate bodies that give the appearance of having the three distinct parts-head, thorax and abdomen-of ants, despite having just two.
elongate: 延長する、引き延ばす
thorax: 胸部、胸郭、(古代ギリシャの)胸甲、胸当て

To complete the charade, the spiders walk on their three rear pairs of legs and raise the fourth pair overhead, waving them around to simulate ant antennae.
charade: ジェスチャー、(ジェスチャーゲームの)動作(で表わす言葉)、見えすいたまねごと、「ジェスチャー」
walk on: (舞台をちょっと歩くだけでせりふのない)端役、通行人役、端役者

They even adopt ants' characteristically fast, erratic, nonstop mode of locomotion in place of the stop-and-go movements other jumping spiders make.
adopt: 採用する、(自分のものとして)取り入れる、(会議で)採択する、(正式に)承認する、養子にする、(…に)養子として引き取る、公認する、指名する

It is an Oscar-worthy performance and the secret of this group's success: more than 200 species of Myrmarachne thrive in the tropical forests of Africa, Asia, Australia and the Americas.

This rich diversity makes ant mimicry the most common form of mimicry.

Yet it is the least known.

New research is exposing the mind-boggling complexity of the ant mimics' charade, however.
mind-boggling: びっくりさせる、肝がつぶれるような

Like the king snake and hoverfly, Myrmarachne species gain a survival advantage by looking like other species-in this case, lethal ant species, because predators of spiders steer clear of both the ants and their look-alikes.
steer clear of: …を避ける、に関係しない

But, it turns out, the spiders pay for that advantage: to give a convincing performance, they must expose themselves to considerable risk.
convince: (…を)確信させる、納得させる、確信させる、説得してさせる
considerable: (量・数が)かなりの、相当な、少なからぬ、考慮に入れるべき、無視できない、重要な、著名な

The evolutionary forces that led to their fakery have left the ant-mimicking spiders living on the knife's edge, walking a fine line between avoiding one enemy and falling prey to another.
fakery: ごまかし、いんちき

In revealing the unexpected perils of mimicry, studies of these remarkable arachnids show the phenomenon of mimicry in a new light.
arachnid: クモ形綱の動物

Faking ItMy fascination with mimicry began one day in 1995 in the office of my then supervisor, Robert R. Jackson, while discussing potential research topics for my master's degree.

Jackson, a spider expert at the University of Canterbury in New Zealand, had cemented his reputation as a leading arachnologist through his work on Portia, a genus of jumping spiders renowned for their mammalianlike levels of clever behavior.
cement: セメント、接合剤、結合、(友情などの)きずな、(歯の)セメント質
mammalianlike: Null

Accordingly, he suggested that I work on a species of Portia.

As an afterthought, he mentioned the antlike jumping spiders found in the tropics.

I was instantly intrigued.

Now, 20 years down the track, Jackson and I are colleagues who share a laboratory and have traveled throughout Africa, Australia and Asia to research these remarkable creatures.

Throughout our journeys we have discovered many unusual consequences of mimicry that underscore just how much more complicated the business of deception is than conventional wisdom would suggest.
underscore: (強調のために)(…に)下線を引く、(…を)強調する、力説する、背景音楽を与える

The standard view originated with English naturalist Henry Walter Bates, who in 1861 provided the first scientific theory to explain mimicry in nature, based on his observations of Amazonian butterflies.

Bates supposed that an edible species that resembled an unpalatable or downright toxic one would gain a survival advantage by tricking potential predators into leaving it alone.
unpalatable: 口にあわない、まずい、受け入れ難い、いやな
downright: まっすぐな、率直な、露骨な、徹底的な、正真正銘の

In Bates's scenario, predators would learn from experience that eating the nasty species was a bad idea.
nasty: (胸が悪くなるほど)いやな、不快な、汚らしい、ひどくいやな、荒れ模様の、意地の悪い、たちの悪い、卑劣な、意地が悪くて、卑劣で

After that unpleasant encounter, the predators would avoid the toxic species and would then avoid the mimics, too-even though the mimics themselves were harmless.
harmless: 無害な、害を与えない、(…に)無害で、害を与えなくて

This parasitic charade, in which one species exploits another's defenses, is now known as Batesian mimicry.
parasitic: 寄生的な、寄生虫性の、寄食をする
charade: ジェスチャー、(ジェスチャーゲームの)動作(で表わす言葉)、見えすいたまねごと、「ジェスチャー」

But it turns out that mimicry does not work exclusively in the simple, straightforward manner Bates described-far from it.
straightforward: まっすぐな、正直な、率直な、複雑でない、簡単な、まっすぐに、正直に、率直に

For one thing, some mimics use their resemblance to another animal not to avoid getting eaten but to deceive their own prey and thus obtain a meal through dishonest signals-so-called aggressive mimicry.
For one thing: ひとつには、第 1 には

And animals exploit mimicry for various other reasons.

No group of organisms illustrates the complexities of the strategy, and the evolutionary forces that shaped them, better than ant-mimicking spiders do.

Upsides and DownsidesTo the uninitiated, ants might seem unworthy of imitation.

But in the tropical rain forest, where their total biomass exceeds that of all vertebrate animals combined, ants are strong shapers of the environment and have great power over its inhabitants.

As such, they are prime candidates for being imitated.

Myrmarachne spiders trade on the ants' fearsome reputations: ants avidly defend their nests by biting or stinging intruders, and an individual can recruit an entire colony to its cause-often with lethal consequences for the interloper.
trade on: 〈付け入る〉・付け込む、〔+前+(代)名〕〔…を〕(悪く)利用する，〔…に〕つけこむ
avidly: 熱心に、貪欲に
stinging: 針をもつ、刺す、刺すように痛ませる、ずきずきさせる、苦悩を与える、苦しめる、しんらつな
recruit: 新兵、補充兵、(…の)新会員、新党員、新入生、新入社員、新メンバー
interloper: (不法)侵入者、干渉する人、おせっかい

Predators are thus wise to avoid trying to eat any prey that look to be such ants.

Yet for the spiders to trick predators into avoiding them, they must take some real risks.
trick into: 〔+目+前+(代)名〕〈人を〉だまして〔…〕させる

For instance, they need to live near the ants to avoid standing out to predators as being not antlike.
stand out: 目立つ、際立つ、すぐれている、(他が屈しても)あくまでがんばる

Living in close quarters, which is unusual for spider species but common in ants, puts the spiders directly in harm's way; if they are found to be fraudsters, odds are they will become lunch.
fraudster: 人たらし、人誑し、暗者、闇者

Having to cohabit with their enemies is not the only price these ant-mimicking spiders pay.

The dissemblers are so convincing that predators that specialize in eating ants-including some other species of jumping spiders-attack them as prey.
cohabit with: (特に)〈結婚していない男女が〉同棲(どうせい)する; 〔…と〕同居する
dissembler: しらばくれる人、ねこかぶり

And competition between males for access to females has raised this predation risk.
predation: 捕食

The choosy females have driven Myrmarachne males to evolve enlarged mouthparts that can increase their body length by up to 50 percent.
choosy: (…に)えり好みして、やかましくて、気難しい
mouthparts: 口器、口器

Exactly why the females prefer a big mouth is not known, although it may be an indicator of health.

At first glance, one would be forgiven for thinking that this enlargement would hurt the spiders' chances of surviving by detracting from their antlike appearance.
detract: (…を)減じる

It does hurt them but not in that way.

The trait makes them look like ants that are carrying something in their mouth.

Because an ant's mouthparts are very dangerous, ant-eating jumping spiders tend to preferentially target ants that are carrying objects in their jaw and that are thus unable to bite their predators.

So although having a big mouth may help male Myrmarachne spiders score with the ladies, it also has the unwelcome effect of making them more attractive to predators.
score with: 得をする、うまくやる、成功する、口説き落とす

The cunning mimics can actively defend themselves against some of these threats, exhibiting a surprising degree of behavioral flexibility.
cunning: こうかつな、ずるい、悪賢い、かわいらしい

For example, when an ant-eating jumping spider initiates stalking, the mimic makes a display toward the potential predator, raising its front legs from their normal antennae posture to a position vertically above the head and staring fixedly at the other spider without moving.
staring: stareの現在分詞。(目を丸く見開いて)じっと見る、 凝視する、 じろじろ見る
fixedly: しっかりと、確固として、じっと

The display seems to communicate that it is a spider or at least that it is not an ant after all.

Whatever the message, it effectively deters the predator.
deter: (おじけづかせて)やめさせる、思いとどまらせる、妨げる、阻止する

Similarly, when a pesky scientist ( and presumably other potential predators ) comes along and tries to catch a Myrmarachne spider clinging to a plant, the mimic will abandon its antlike behavior, drop off the vegetation and hang out of sight on a thread of silk-the best of both worlds.
pesky: やっかいな、いやな、うるさい
come along: やってくる、(…と)一緒に来る、ついて行く、同行する、急げ、がんばれ、もっとしっかりやれ、まさか!、それはないよ!、(…が)(うまく)進む
clinging to: 付着、附着

One particularly Machiavellian species of ant mimic, Myrmarachne melanotarsa, gets the best of both worlds in yet another way and upends the notion that parasitic and aggressive forms are separate phenomena that arise from distinct selective pressures.
upends: upendの三人称単数現在。逆さに立てる
distinct: 他とまったく別な、別個の、性質が異なって、はっきりした、明瞭な、明確な、紛れもない
selective: 選択的な、精選する、選択眼のある、(…に)選択的で、(…を)注意深く選んで、分離感度のよい

The spider's resemblance to ants is so terrifying to other, ordinary jumping spiders that in addition to avoiding predation, M. melanotarsa uses its antlike appearance to capture prey.

It drives hapless jumping spider mothers out of their nests; then it penetrates the nest to raid the eggs or the brood of spiderlings.
hapless: 不運な、不幸な
mother out: Null
raid: (占領目的ではなく、相手に打撃を与えるための)不意の襲撃、奇襲、空襲、(警察の)手入れ、(略奪を目的とする)侵入、(競争会社などからの社員の)引き抜き、売り崩し
spiderling: 【名】《昆虫》クモの子

Ants have trouble raiding spider nests because their legs get caught in the spider silk, but spiders have adaptations that enable them to negotiate the sticky strands-and M. melanotarsa takes full advantage of them.
strand: 座礁させる、立ち往生させる、行き詰まらせる、する

Learned or Instinctive ? To fully tease out the forces that have caused mimicry to evolve and take the forms it does, researchers need to know the factors that cause predators to avoid imposters.
tease out: ...をほぐす；解く

Back in the 1800s, Bates thought that the predator must experience, in some way, the danger posed by a creature that another organism is mimicking before it grasps that it ought to steer clear of the real McCoy and anything that looks like it.
ought to: なければなりません；ねばならない、するべきだ
steer clear of: …を避ける、に関係しない
the real McCoy: 『ブロンディー/女銀行強盗』（原題：The Real McCoy）は、1993年制作のアメリカ合衆国のクライム・スリラー映画。

But here again the ant-mimicking spiders flout that conventional wisdom.
flout: ばかにする、無視する

The ordinary jumping spiders that abstain from eating both ants and Myrmarachne do so from instinct, not as a result of learning through bad experiences.

In other words, the forces that shape evolution have baked that avoidance into the predators' hard wiring.
bake: 焼く、(…に)焼く、焼き固める、(強い日ざしで)肌を焼く、からからにする
hard wiring: ハード配線

In hindsight, this avoidance instinct is not surprising: after all, if you die in an encounter with an ant, there is no room for learning.
hindsight: あと知恵、(銃の)後部照尺

In some ways, it is easier to envision how hardwired avoidance could have evolved: predators that happen to dislike approaching ants are more likely to survive and reproduce, and their genes get passed on; ultimately instinctive ant aversion dominates the population, and those that lack the trait are quickly weeded out by the ants themselves.
envision: 心に描く、直面する
reproduce: 再現する、再生する、(…を)複製する、複写する、繁殖する
aversion: 嫌い、(強い)嫌悪(けんお)(の情)、いやなもの
weed out: 淘汰する、除去する、篩い落とす、〈無用なもの・有害物などを〉〔…から〕除く、淘汰する

A Glorious MessThe complexity my colleagues and I have discovered in the mimicry system of Myrmarachne serves as a cautionary tale: the tangled principles at work here almost certainly apply to other cases of mimicry.
serve as: 為る、役に立つ、間に合う、成る、仕える、つとめる、…の代わりになる、〈…として〉〈人の〉役に立つ、〈…を勤める〉・為る、役を勤める
cautionary: 警戒的な、訓戒の
tangled: tangleの過去形、または過去分詞。(…を)もつれさせる

And we still have much to learn.

Scientists have tended to view mimicry in terms of its being an adaptation to selective pressure from a single predator using a single sense: vision.
selective pressure: 選択圧
single sense: Null

( Because humans are so dependent on vision, this sense tends to be the one researchers focus on.

) But we now know from Myrmarachne that multiple predators shape a mimic species: my own work has shown that ordinary jumping spiders and mantises are influential in this regard; birds, lizards and frogs probably are, too.
mantis: カマキリ
influential: 勢力のある、有力な、(…に)(大きな)影響を及ぼして
regard: (…を)みなす、考える、(ある感情をもって)(…を)見る、眺める、(…を)注視する、じっと見る、(…を)顧慮する、(…に)注意する

And studies of other creatures hint that mimicry can involve smell and sound, among other senses.
in this regard: その際、其の際、この[その]点について(は)
hint: ほのめかし、暗示、ヒント、かすかな兆候、わずか、有益な助言、心得

For example, a palatable species of tiger moth mimics the acoustic signals of a noxious one to avoid predation by echolocating bats.
palatable: 味のよい、口に合う、趣味にかなう、快い

And some butterfly species copy the chemical signals emitted by ants to enter their well-defended nests, where the butterflies deposit their eggs for safekeeping.
deposit: (銀行・金庫などに)預ける、預金する、預ける、置く、(…に)腰を下ろす、産みつける、(…に)堆積(たいせき)させる、沈澱させる、(…を)手付金として支払う

Excitingly, scientists now have the technology to probe the sensory experiences of other species.
sensory experience: 知覚経験｛ちかく けいけん｝、感覚的経験｛かんかく てき けいけん｝

High-frequency recording devices allow researchers to visualize noises above our own hearing threshold-including those emitted by tiger moths and bats; mass spectrometry lets them see the hydrocarbon profiles of ants and their mimics, providing a picture of their chemical interactions.

Applying these techniques to the study of mimicry and other natural phenomena will no doubt expose more of the spectacular solutions and trade-offs that have evolved in the eternal arms race between predators and prey.
spectacular: 見せ物(的)の、壮観な、目覚ましい、華々しい、劇的な

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