Melee units are debatably the most dependable units. Their attacks miss less than every other method of attack, and melee units have the best natural stats of all the types in the game, and due to their high defensive prowess, can fight and destroy multiple enemies during the enemy's turn just by counter-attacking, while gun* and cannon units must attack only once per turn.
The rhino beetle and pillbug have high defense and excellent attack. Only the rhino beetle can equip other weapons or status gear on his weapon slot, and they all have very low movement capabilities, but enough to get into position when already in the battle. They excel at charging up to the front lines and hoping to get attacked so that they can counter. Each does this in different ways.
These versatiles are essentially true versatiles. While they have excellent gun stats, guns in general do poor damage. When equipping any weapon but one central one, they also have to lower attack power and defenses quite a bit. They don't gain beam attacks, which they obviously have available in their guns, but do gain great bonuses in their melee weapons. They both have excellent mobility, and higher than average defenses, but are not good at countering like other melee drones.
As a flying unit, the bee is unique in that it can attack enemy drones from the water or difficult terrain. The bee trades in power for mobility, noticable 20 points lower accuracy. The bee has possibly the most potent defense in the game statistically, but is exempt from terrain bonuses, which frankly doesn't have much of an effect on her due to the high other stat, and also has the mobility to reduce hits when she needs to and the fourth highest speed.
First are the versatiles which would like to think they're good at melee attacks, but really aren't, like the locust (117), centipede (117), and especially the cockroach (88!!). The butterfly and dragonfly have their own weak melee weapons, and the moth is synonymous with the scrap fangs, while the locust and ladybug are synonymous with the drills, the two most prominent group melee weapon sets. Only the cicada, dragonfly, and firefly are specifically not intended to equip melee weapons. Even despite the fact that melee weapons create the weakest type of attack when weak, due to natural accuracy and a steep raising requirement.