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。
参考例句
1. A snake wormed on the wet ground. 一条蛇在潮湿的地上慢慢爬行。
2. The early bird gets worm. 早起的鸟儿有虫吃。
3. Early bird gets the worm. 早起的鸟有虫子吃。
英英解释
n.
1. any of numerous relatively small elongated soft-bodied animals especially of the phyla Annelida and
2. a person who has a nasty or unethical character undeserving of respect
3. a software program capable of reproducing itself that can spread from one computer to the next over
4. screw thread on a gear with the teeth of a worm wheel or rack v.
1. to move in a twisting or contorted motion, (especially when struggling)
