We use the word ‘bug’ colloquially to mean any small animal that has more than 4 legs, or non at all. All insects are considered bugs and so are spiders, millipedes, worms, slugs and crustaceans. It’s a derogatory term for small things that bug us.
The word is used scientifically to refer to a large family of over 80 000 species of Insects including Cicadas, Leaf Hoppers and Shield bugs. The Boxelder Bug is a True Bug.
They make a stink when disturbed so they are safe from predation which makes it OK for them to congregate in large Boxelder gatherings on the sides of Maple trees. They eat Maple seeds and sometimes spend winter inside human homes.