A V Leeuwenhoek

Silver mirror test /Tollens test is generally given by compounds having aldehydic group (aldehydes,alpha-hydroxy ketones and formic acid-its -COOH behaves like a aldehydic group).
Tollens reagent is ammoniacal solution of silver nitrate ie it's a solution of silver nitrate and ammonia.

When an aldehyde is introduced to the Tollens reagent, two things occur:

1) The aldehyde is oxidized by the Tollens reagent and forms a carboxylic acid.

2)The silver ions present in the Tollens reagent are reduced into metallic silver. Generally, the Tollens Test is carried out in clean test tubes made of glass. This is because the reduction of the silver ions into metallic silver form a silver mirror on the test tube.

All of these are insects.