Beetles and bugs. They're not the same.
All bugs are insects but not all insects are bugs.
All beetles are insects but no beetle is a bug.
(There'll be a test on this later.)
Bugs (order Hemiptera) include aphids, cicadas, leafhoppers, stink bugs, assassin bugs, shield bugs, water boatmen and giant water bugs. They are liquid feeders in which the mouthparts are modified into a long tube (rostrum). You can see the rostrum on this slightly dazed, juvenile Dindymus. It's the fine black tube running back from the head between the bases of the legs. When feeding, bugs insert the rostrum into their plant or animal meal and suck up sap (aphids), blood (bedbugs) or sloppy innards (assassin bugs). They can't consume solid food.
On the other hand, beetles (order Coleoptera) eat a range of foodstuffs from wood to fungus to living animals to rotting corpses. They handle the chunky stuff with chewing mouthparts. These are not so easy to see on this tenebrionid beetle but it's obvious there is no rostrum. The mouthparts are a teensy bit more apparent on this carnivorous carabid.
Part II—The other side—tomorrow.