"There are flies there."
Based on the DuoLingo course and the comments I've seen from native speakers, your statement is not entirly correct. According to one Russian, "есть" is required in some phrases, prohibited in some and optional in others. And DuoLingo specifically taught us that "здесб есть яблоко" is the Russian translation of "there is an apple here". My question is, why does Duo require "есть" with "here" but prohibit it with "there"?
I'm not very advanced in Russian, but my understanding is that the first "there" in "there is," which is like the Spanish "hay" does not need to be used in in Russian in the present tense (In fact, kpferdeort, below, says it ISN'T used, not just that it doesn't have to be used), and that the second "there" is clearly given by "tam."
In android version, I think it should actually give the hyphen option, for, as far as I understand, the phrase would be wrongly hand-written in without it (in my tab it doesnt let me write in every question, most is a "select the right words and word order from a list" kind of answer