We owe a lot to the birds and beasts who eat insects but all of them (which are) put together kill only a fraction of the number destroyed by spiders.

owe ^欠、感谢

• How much do I owe you? ^{我欠你多少钱？}
• You owe him an apology. ^{你欠他一个道歉。}
• I owe you one. ^{我欠你一个人情（IOU）。}
• I owe you a lot / a great deal.  ^{表达“感谢”}

How much do I owe you? Well, that'll be eighteen dollars and seventy cents. No charge for the cleanup. It's on the house.  ^走遍美国
I feel like I owe you an explanation. I don't ordinarily go around kissing guys at parties. ^老友记

Albert Einstein once attributed the creativity in a famous scientist to the fact that he never went to school. There is undoubtedly a truth in his observation, but such a truth is not criticism of schools.

beasts who eat insects = insect-eating animals ^{上文中的同义词替换}

• The lorry was loaded with empty beer bottles and hundreds of them slid off the back of the vehicle and on to the road. ^{上义词；同义词不好替换，用上义词替换}
• There was also a great deal of machinery on display. The most wonderful piece of machinery on show was Nasmyth's steam hammer.
• Giant pandas are considered a national treasure and the Chinese government are doing their best to protect this endangered species.
• Moreover, in the past two years other nearby cities may have begun to build similar golf courses or resort hotels. Indeed, the fact that Ocean View has already built these facilities might actually portend failure for Hopewell, …

fraction ^{一小部分 a small amount of sth. …的一小部分}

• His shares are now worth only a fraction of their former value. ^{他的股票现在只值原来价值的一小部分。}
• It's usually a small fraction of the total. ^{它通常只是总数的一小部分。}
• We are lucky in that only the lower fields, which make up a very small proportion of our farm, are effected by flooding, …

• a high / large proportion / percentage of ^{… 一大部分}
• a small / tiny proportion / percentage of ^{… 一小部分}

All of us put together earn only a fraction of the money made by Bill Gates. ^{我们所有人加在一起挣的钱也不过是比尔·盖茨的一小部分而已。}

Moreover, unlike some of the other insect eaters, spiders never do the least harm to us or our belongings.

insect eaters ^{吃昆虫的(再次被替换)}

• beasts who eat insects
•  insect-eating animals 

moreover ^{此外；递进}

• Moreover, spiders never do harm to us. ^{此外，蜘蛛从不伤害我们。}
• Moreover, you're a social being.^{而且，你是个社会人。}
• Moreover, there was no evidence of adaptability to the noise.^{此外，没有证据表明我们对这种噪音有适应性。}

to make things / matters  worse ^{更糟的是… （有感情色彩）}

• The team has lost the last two games and, to make matters worse, two of its best players are injured. ^{非谓语动词如果是固定习语，不要考虑主语统一}
• To make matters worse, the room is rather small, so I have temporarily put my books on the floor.
• During these tests she was able to read a newspaper through an opaque screen and, stranger still, by moving her elbow over a child's game of Lotto she was able to describe the figures and colours printed on it; … ^{【扩展】stranger still 更奇怪的是}

unlike ^{不像；与…不同(dislike 不喜欢)}

• Unlike his brother, he is very outgoing. ^{与他哥哥不同，他很外向。}
• Unlike most birds, ostriches cannot fly. ^{与大多数鸟不同，鸵鸟不能飞。}
• Unlike other cars, this model is electric. ^{与其他汽车不同，这款车型是电动的。}

do (no) harm to ^{对…有(无)害}

• These chemicals do harm to your health. ^{这些化学物质对你的健康有害。}
• Noise pollution can do harm to wildlife. ^{噪音污染会对野生动物有害。}
• Careless disposal of waste does harm to the environment. ^{乱扔垃圾对环境有害。}

never do the least harm to ^{完全无害（Never + 最高级 = 完全...）}

• I have no idea what to do next. ⇒ I don’t have the foggiest idea what to do next. 
• I have no interest in boxing. ⇒ I don’t have the slightest interest in boxing.
• This doesn't bear the slightest resemblance to anything in real life. 
• Vaccines never do the least harm to patients. ^{疫苗对患者完全无害。}
• These shoes never do the least harm to hardwood floors. ^{这些鞋子对硬木地板完全无害。}
• The software never does the least harm to system performance. ^{该软件对系统性能完全无害。}

双否=强肯

• No one can avoid being influenced by advertisements.
• No one knows how long it will last.
• But this does not matter, for, as he has often remarked, one is never too old to learn.