这些名词均含“虫，昆虫”之意。
bug: 指小昆虫，尤指吸血的臭虫，也可指细菌。
insect: 含义广泛，多指蚂蚁、黄蜂、蝉等等。
pest: 指有害的昆虫或有害的小动物。
worm: 侧重指蚯蚓、蚕、毛虫等小而无骨的虫。
名词 pest:
a serious (sometimes fatal) infection of rodents caused by Yersinia pestis and accidentally transmitted to humans by the bite of a flea that has bitten an infected animal同义词：plague, pestilence, pestis
any epidemic disease with a high death rate同义词：plague, pestilence
a persistently annoying person同义词：blighter, cuss, pesterer, gadfly
any unwanted and destructive insect or other animal that attacks food or crops or livestock etc.
例句：
That child is an absolute pest!那孩子讨厌极了！
Stores of grain are frequently attacked by pests.储存的谷物经常受到害虫的破坏。
