Dendro means tree. I am not sure what genius decided the genus Dendrobates were treefrogs (they are not).

I think and speak in scientific names unless I don't know it - in that case I use the common name. I only do this because there's no confusion - the scientific name is universal, even across languages. Of course, if the person doesn't know the scientific name I can always try the common name if I know it. I honestly don't know many of the common names. The scientific name business isn't hard - once you do it for a while you find you can learn others more readily.