Why does Antlr name something, with a leading underscore?

[Korporal]

I have this parser rule:

translationUnit
  : BYTE_ORDER_MARK? uses* (Scopes+=scope | Traits+=traits | PassiveStatements+=passiveStmt)* EOF // BOM is skipped by lexer, but we mention here
  ;

In the generated C# code it creates List<T> members named _Scopes and _Traits and _PassiveStatements but why the leading _ character? how can I stop it from prefixing the names like this?