Natural Order and Science

[Harris]

However, virtual particles are not detectable by any mean and for that reason in the world of physics they are called “virtual.” They are mathematical objects which scientists have invented for the purpose of calculations of interactions between real particles and it is absolutely inappropriate to treat them as a different category of real physical particles which are detectable.

There is no such thing as a 'particle'.  What is referred to as particles are 'regular' fluctuations of a field, whereas "virtual particles' are irregular fluctuations of a field.  And they are both real and detectable.  Else how would we know they are there?

Virtual Particles: What are they?

Please explain how virtual particle are similar to fluctuation of a field. Also clarify about which field we are talking and what exactly is that field.