I recently labeled and placed in the appropriate boxes approximately 40 insects, so my collection is looking a lot more respectable now. Here are the big four: Diptera, Lepidoptera, Hymenoptera, and Coleoptera, along with Hemiptera and Orthoptera because they look cool. The next entry will feature an antlion, a specimen sent by Kit's mother in Virginia - they are extremely interesting, so don't miss it! After that I am considering featuring more Cerambycidae and a notable garden pest, but I can't give everything away.
Why are Coleoptera, Lepidoptera, Hymenoptera, and Diptera labeled "The Big Four" insect orders? Well, the quick answer: they contain the largest proportion of insects, and have the greatest diversity. Coleoptera, or "beetles", make up 1/5 of all known animal species, and 40% of all known insects. Lepidoptera contains 180,000 known species. Hymenoptera has just over 100,000 known species worldwide, while Diptera is the fourth most diverse, with 100,000 known species. All four are also holometabolous, meaning they have one sudden change from larval to adult stage, instead of the hemimetabolous insects which gradually molt until they reach their adult form. Holometabolous insects are thought to have an advantage because their adult and larval forms are so distinct - the larvae usually live in different habitats and have different feeding habits from the adults, so there is no competition for food or space. Also, all four are pterygotes, meaning they can fly and thus disperse and exploit a greater variety of habitats and ecological niches, contributing to their diversification. Since I also enjoy spreading insects, and the diversity among Hemipterans, here are two other favorites: