Something is biting my family. We can't see it but it itches like crazy.

The bites are in no particular area of the body. They're all over but more on the inner thighs and torso.
Today I went to use my blue mint Listerine and found tiny little black bugs under the cap! I found this to be strange.
Can anybody tell me what this is??

Something is biting my family. We can't see it but it itches like crazy.