You can spite a Chinese character to many parts.For example 蚂. You split it two parts like虫+马. left part 虫 means insects. So we can guess that the character 蚂 means a kind of insect.And the right part 马 is the pronunciation of the character.So it pronunce "ma". Except these three words you give,we can see another word “妈”.The character means "mother" in China,the pronouncation is "ma".left part of "妈" is "女"，it means female. Chinese characters, always one part of it used to represent the means and other part of it used to pronunce.

Maple answered your question very well! I just want add to it that Chinese words are normally bisyllabic rather than monosyllabic, this means one word is made up of two characters with similar meanings. e.g. "一只蚂蚁"(an ant), You can't say "一只蚂". "蚂蚁" is a bisyllabic compound meaning the same as 蚁, 蚂 is used here in a supportive manner. represents partial meaning of the word "蚁", like "insect". This kind of Chinese morphology is called "Semantic Replication/Duplication", very common in Chinese language. Analogically 砝码 玛瑙 etc... hope this helps.. please tell me if I am wrong~ thank you

by the left part where is different. 90% chinese characters are comprised like that called 形声字.(shape-pronunciation word). the three are shape-left + pronunciation-right. as you see, the left three parts are 石 王(玉) and 虫 which mean stone jaspers and insects and the right 马 is pronunciation. 码 is a kind of stone which use to measure weight, eg 砝码(metal now). 玛 often used as 玛瑙 is a kind of jasper. 蚂 is ant, a kind of insect. very easy, isn't it?