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蜻蜓幼虫可以感知捕食者的存在，虽然这使它们更加安全，但却使它们的死亡率高于一般未感受到压力的幼虫。
A hungry fish can kill prey with a quick bite. That is, of course, if its prey hasn't already died of fright. Take tasty dragonflies. The mere presence of predators—even caged ones—is enough to scare dragonflies to death, according to a study in the journal Ecology. [Shannon J. McCauley, Locke Rowe, and Marie-Josée Fortin, "The deadly effects of ‘nonlethal’ predators"]
一条饥饿的鱼能够一口咬死其猎物。当然，前提是经过一番殊死搏斗之后猎物依然健在。以有趣的蜻蜓为例，根据《生物学》杂志的一篇研究报告，捕食者的出现能够将蜻蜓吓死，哪怕这些捕食者被关在笼子里面。 [Shannon J. McCauley, Locke Rowe, Marie-Josée Fortin, 《非致命捕食者的“致命”效果》]
Researchers collected wild dragonfly larva, and placed them in tanks with fish or insect predators. The larvae could see and smell their hunters—but were kept safe by underwater cages. After two months, the researchers took a head count—and found that dragonfly larvae sharing quarters with their killers were two to four times as likely to die off, compared to counterparts living in predator-free waters. And they had slimmer chances of surviving metamorphosis, too.
研究者将野生蜻蜓幼虫放进装有鱼类或昆虫类捕食者的容器中，具体的安放位置是在水下的笼子里，这里有绝对的安全保障，但同时幼虫们也能够看见并嗅到它们的天敌。两个月之后，研究者发现，与捕食者同住的蜻蜓幼虫死亡率是正常蜻蜓幼虫的2-4倍。而且它们蜕变的存活率也更低。
The authors suggest a couple reasons why. First, prey tend to make fewer forays for snacks when predators are lurking around, so they may not be as nutritionally fit. And previous studies have shown that the presence of predators ups stress levels in prey, weakening their immune systems and making them more vulnerable to disease—and death.
文章的作者提出了几点原因。首先，当有捕食者在场时，处于劣势的被捕食者会减少觅食行为，所以它们的营养状况不佳。加上之前的研究表明，捕食者的出现使被捕食者的压力水平升高，降低了它们的免疫系统机能，使它们更易生病乃至于死亡。
As if being eaten wasn't enough to worry about, looks can kill too.
正所谓：死不足惧，怕死堪忧。看来生物界的规律是相通的。
mere n. 浅湖; 池 larva n. 幼虫 counterpart n. 相应物 lurk v. 潜藏, 埋伏 nutritionally adv. 滋养地
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