下面这个句子，在 there be 之间插入了 are known to：

There are known to be thousands of different species of beetles.

类似的好像还有：

There was said to be a fire in that building last night.

引句中在 there be 之间插入了 was known to。

请问：上面两句中的 thousands of different species of beetles 和 a fire 是什么句子成分？是主语吗？