Re: Is it SHB?
They might be wax moth larvae. If you didn't see any inside the hive when doing your inspection, wax moths would be my guess. If you leave the corrugated plastic sheet beneath the screened bottom it allows wax moths a place to freely lay eggs...and those larvae seem to survive on dropped pollen and other debris.
Why do you have the sheet in this time of year?
PS I never see varroa on mine either, unless I coat it with Pam or something sticky.....and my hives have plenty of mites. Zero mites on a nonsticky sheet means doodly.
Let me never fall into the vulgar mistake of dreaming that I am persecuted whenever I am contradicted. - Emerson