Hello. Actually I cannot understand: why "here is smt" is met almost nowhere? Sometimes I see that people prefer to say "there is smt" instead of "here is smt", even an action is happening or a thing is located in an one room, where a saying human is too. May I say "Here Is a bug in this room" for example, considering I'm in the room too,or should I use "there is construction anyway?

See a translation

The difference between "here" and "there" as subjects is not the same as the difference between "here" and "there" as objects. We only say "Here is X" when we are giving X to someone, or showing X to someone. For example, "Here are the car keys" is something you might say when giving someone car keys. But when you want to say "X exists in a certain place," the only way to say that is "There is X in that place."
"There is a fountain in the garden."
"There are some cookies in the kitchen."
"There was a pile of garbage on the sidewalk."

If you are in the same place as the thing you're talking about, you can add "here" later in the sentence:
"There is a fountain here in the garden."
"There are some cookies here in the kitchen."
"There was a pile of garbage here on the sidewalk."