it not a matter of hearing it. It is known fact, This article will explain it. https://exhibits.library.duke.edu/exhibits/show/insects/size-o#:~:text=As%20an%20insect%20grows%20it,much%20smaller%20than%20normal%20size.
there was a complaint in a previous comment ((you spelled ‘disappeared’ incorrectly))
Both from field observation and lack of evidence leads to the article by the Guardian to be problematic. In the third paragraph, it says this: " Estimates vary and are imprecise, but it seems likely that insects have [declined in abundance] by 75% or more since I was five years old." This would be a very localized experience and not a global one, Most subsequent articles are similar. This includes academic ones like this one: https://press.princeton.edu/ideas/insect-apocalypse. There is in many area of the world a notable decline. This reports are based on measurable data. A global decline would require a lot of data to determine, not just localized experiences. A joint, global project spanning many years, and all continents would ultimately be required. Specific Evironmental niches, population fluctuations, weather, historical data and much more would be required.
I didn’t respond to any complaint, I just fixed what I felt was a typo and I made a public note so that the change wasn’t mysterious.
I personally am of the opinion that we should increase the oxygen level of the atmosphere, so that insects become bigger and I can take better photos with my less-than-ideal macro setup
But the article did - make more people aware that insects have value, and the numbers are declining - and that has a ripple effect.
A little like killing sparrows followed by the Chinese famine.
I can’t see it happening. They are all over the land and in the sea. It’s only a thought experiment. But,…
The Earth’s system would adapt/change to something else where arthropods weren’t a big part of things. Maybe something else would fill the spots that arthropods inhabit now the way mammals and avian dinosaurs filled in the gaps when non avian dinosaurs were wiped out. But, since arthropods were so successful, they would probably make a comeback.
I just realized that I posted this in the wrong thread. I thought I was in https://forum.inaturalist.org/t/what-would-happen-if-every-species-of-arthropod-grew-five-times-bigger-overnight/55978/24. 
That would be a great idea, until you start a fire, light a match, or a volcano erupts! It would be interesting, unfortunately it would take quite some time for the insects to evolve to the Carboniferous Period Arthropodic sizes.
That can be arranged. I have no plans for the evening, so they have about 6 hours :P