背景介绍

【背景】

萤火虫发光的原理

夜晚人们可以看到萤火虫一闪一闪地飞行，这是由于萤火虫体内一种称作虫萤光素酶的化学物质与氧气相互作用，从而产生的光亮。这种被称作虫萤光素酶的化学物质像开关一样启动这种反应，当萤火虫产生虫萤光素酶的时候，这种反应就开始了，萤火虫便会发出一闪一闪的光亮。

荧火虫的种类很多，在它们的腹部末端都有一个能发出绿色光辉的发光器官。它们白天伏在草丛中，夜晚飞出来活动。尾部的那盏绿色的小灯，把夜空装点得同幻境一般。难怪有人看了会害怕。荧火虫不仅成虫可以发光，就连卵、幼虫、蛹也会发光。成虫的腹部末端有个发光器。雄虫的发光器为两节，雌虫为一节。在发光器的透明皮肤下面有发光层和反光层。发光层呈黄白色，是一种叫作荧火素的蛋白质发光物质。当荧火虫呼吸时，这种荧火素便和吸进的氧化合成荧光素酶，于是，它们的尾部就开始一闪一闪地发光了。

能够发光的生物还有海洋中的藻类和萤科的其它昆虫，它们都是利用虫萤光素酶与氧气产生反应，从而发出光亮的。

萤火虫发光的原因

第一，发光是为了求偶。由于不同种类的萤火虫，发光的型式不同，因此在种类之间自然形成隔离。萤火虫中绝大多数的种类是雄虫有发光器，而雌虫无发光器或发光器较不发达。雌雄之间发光相互吸引追逐，寻找自己满意的对象。

第二，发光是为了吓唬敌人。1999年，学者奈特等人发现，误食萤火虫成虫的蜥蜴会死亡，证实成虫的发光除了找寻配偶之外，还有警告其它生物的作用；学者安德伍德等人在1997年以老鼠做的试验，证实幼虫的发光对于老鼠具警示作用。

英文原文

【原文】
This week on Why? Tell Me Why! We are answering a viewer question as to why lightning bugs light up.

Lightning bugs light up basically to find a mate. It’s a way that lightning bugs communicate with

each other, to call each other together, because someone’s looking for a mate. They have these

features in the abdomen of the body: they light up and they can control when they light up, when

they blink and how long they blink. And they use that blinking signal to attract each other.

Do both males and females have the lights?

They both have the lights, but the females have brighter lights and bigger lights because they are

the ones who are trying to attract males to them. Each different species of lightning bug has a

different pattern of flashing to only attract its own species. In this way, if there are five

different species of lightning bugs all in the same field, they can tell who is their same species

and who is not. So, they know who to be attracted to. There is an enzyme in these insects called

luciferase. And it uses something that insects make from the food they eat to bind together and

generate light with very little heat. So, one of the interesting things about fireflies is they

generate this light without making heat.

The only time we see lightning bugs lighting up is when they are on a quest to find a mate? That’s

a, that’s one time they'll use their lights?

There is one other time when lightning bugs will use their lights and that is there is one species

of lightning bugs that uses the light to attract other lightning bugs which she will aim to eat.

The only time we see lightning bugs lighting up is when they are on a quest to find a mate?
我们唯一能看见萤火虫发光是他们求偶的时候。

这个句子是个简单句，谓语是be动词is，主语是the only time，when引导的从句作is的表语，而we see lightning bugs lightning up为定语从句，修饰主语the only time.

time这个词大家应该都不陌生，都知道它有“时间”是意思，不过time可不仅仅只有这一个意思哦

最后呢，time还可以表示加减乘除中的乘的意思，
如：Five times six is thirty.（五乘以六等于三十。）

(可可英语版权所有,未经允许请勿转载)