So, what is the Bug-type?
All self-respecting RPGs have some sort of Insect enemy. From stuff like the Assassin Bug from Dungeons and Dragons to Hornets, Black Widows and Bte Bugs of Final Fantasy to Vermin race of Shin Megami Tensei, all good ol' role playing games give you some Bugs to punch out. Bugs in Pokémon are only slightly different. This is due to Pokémon's mechanics origins. You see, when Mr. Tajiri was a young boy, he was fascinated with bug catching. In Japan, you of course don't just catch bugs, you also fight them with each other. And they can fit into your pocket. Gee, no wonder this franchise is the way it is.
Anyways, Bug-type doesn't still differ much from insectoid enemies you face in other RPGs. They still have the same association with Poison and Flying, they are still weak to most elemental magic and non-conventional physical attacks, and they still largely experience fodder for your adventure. While Pokémon successfully turned Bug-type into its own element largely by syncretizing with the Three Worms of Taoism and expanding its "vermin" status, thus inspired others to do to so, Bug-type is still pretty much the worst type in the game.
The History of the Bug-type:
In the original games Bug-type was designed to be pathetic. Bug-type had only one useful move, Twineedle, which was exclusive to Beedrill. The rest were Leech Life, String Shot, and Pin Missile, all terrible moves improved in the last two generations. The species with the exception of Butterfree didn't have much other types to abuse either, owing to archaisms of the original game. While the species did their role as early route fodder admirably, this caused an issue for Safari Zone bugs. Nonetheless, in this generation, Bug-type got most of its basics, and a fairly rare type combination at the time, Bug/Grass.
Bug-type was important however for two reasons, one was the odd relationship it had with Poison, where both types were super-effective against each other, which was reversed in later generations. Another was that Bug-type was the only type that could damage Psychic-type. Why that is remains a mystery as it is hypothesized that Ghost was supposed to be super-effective against Psychic, but instead Psychic was immune to Ghost-types(which were only one family and had terrible moves to work with, in addition to the Physical-Special not happening yet.) However since all Bug-types were weak to Psychic-types in some manner or other, this didn't come to effect, and Psychic-type remained supreme, while Bug remained a gimmick.
The next generation was not exactly kinder to Bug-type. While there were some powerful Bug-types introduced there were also some terrible ones like the early route ones, and Yanma. Scizor also failed to live up to the hype as it had no moves to abuse, despite its good typing. Nonetheless, Bug-type got its first TM in this generation, Fury Cutter, alongside sexually ambiguous Bug Expert Bugsy. Fan favourite gimmick Pokémon Shuckle was also introduced in this generation, and Ariados kept following Beedrill's steps with its own signature move, Spider Web.
Some species were hampered negatively with the Special split, however. Venomoth lost its 90 Special Defense for 75 Special Defense, and Parasect lost its 80 Special Attack for 60 Special Attack. This made these two Species significantly weaker than their original distributions. Scyther and Pinsir were also granted the same BST, while in original games Pinsir had higher BST.
Due to type chart changes, Bug-type was no longer weak to Poison, but neither was Poison. With the introduction of Steel as well, Bug gained two types that would resist both its associated types, Grass and Poison as well as itself. Nonetheless, Bug-type gained some compensation. It could now hit Dark-type super-effectively, giving Bug-type another paranormal-type to deal with.
To compensate for their terribles, Bug-type was given some decent Abilities to work with such as Shed Skin, Shield Dust, Speed Boost and Compoundeyes. Some of these Abilities remain exclusive for Bug-types. Another one-time buff for Bug-types was the introduction of Bug Experts, who would use late-game and mid-game Bug-types, as an upgrade to the conventional Bug Catchers. However, they did not survive for further generations, ignoring ORAS.
The fourth generation with Bug-type's first great revival. Bug-type suffered greatly from being a Specially oriented group that belongs to a Physical type, but with the split, Bug-type gained several powerful moves to abuse, all of which were available to other species through TMs and Tutors. Most famous one of these moves was U-turn, an instant-switch move that hits the opponent with a decently powered attack first that was available to variety of species, but most importantly to Flying-types. Others like Signal Beam and X-Scissor were largely used as coverage for other types. But in addition to this, the type upgraded three of the strongest Bug-types in the game, Pinsir, Heracross and Scizor, and added one more, Yanmega, a cross-generational evolution to Yanma.
In terms of other stuff Bug-type didn't get much. Tinted Lens remained somewhat unique for the type but it got distributed to elsewhere later. Dry Skin helped Parasect but that was it. Technician did not see much distribution outside of Scizor, and the rest of the Bug-types introduced this gen were either mediocre but better, or not a Bug-type, in the case of Skorupi. This made the new Bug-type Elite Four member Aaron's team even weirder, and solidified Bug's sad status as a classification type, rather than an elemental one.
The next generation was not as big as the previous one, but still it was pretty big. For the first time in the series, early Bug-types were treated as regular third stagers, instead of glorified second stagers to a three stage Pokémon. In addition, the mid-game Bug-types were just as powerful as other mid-game Pokémon from other types. Most notoriously however, Bug-type gained a Mythical, Genesect and a pseudo-pesudo-legendary, Volcarona, who served as the Champion's and his grandson's signature Pokémon.
Hidden Abilities were all over the place for Bug-types, as well. Volbeat and Illumise got access to Prankster which made them much powerful than before, Armaldo got Swift Swim but not much of a use from it, Moxie Heracross was ridiculous for the early metagame, and Keen Eye Skorupi was just sad. But the biggest event was the new moves, including Quiver Dance, a move specifically designed to buff early route Moths, and some Grass-types, and Rage Powder, a variation on Follow Me. Struggle Bug and Steamroller were interesting on paper, but far too weak to do anything.
Sixth generation was largely a loss for Bug-type. Bug-type was forced to early Gym status again, and had only one new representative, with the rest being Megas of the original three great Bugs, and later for Beedrill. Struggle Bug, Pin Missile and String Shot were all buffed to become useful. Some early Bugs that didn't gain Quiver Dance were instead given Sticky Web, a new entry hazard that cuts opponent's speed. Fell Stinger and Infestation were added, and Vivillon became the first early route Bug that had event exclusive forms.
There were also stat updates to the third stage Bug-types, but they were largely janitorial updates that made them better, rather than great updates that made them significant. However, Megahorn saw some more distribution, and Venipede was given Speed Boost as a compensation for not getting either Sticky Web or Quiver Dance.
And of course, Fairy-type. Fairy-type did not help the type at all, as it took Bug's role in defeating Dark-types and resisted the type. While some Bug-types enjoy the Fairy moves they gained, those are only a few.
The next generation was another janitorial update. Several new powerful Bug-types were introduced, but none of them were strong enough to make the cut, except the Ultra Beasts. Three new moves were given, but two were exclusive and one was relatively rare. Nonetheless, Fell Stringer got a slight update that made it viable, and Leech Life got a massive update, becoming another major TM.
In terms of stat updates however Bug-type was a bit more lucky. Volbeat and Illumise got significant stat updates, Ariados got a minimal update and Masquerain got one of the largest updates in this generation. Wormadam forms also gained access to Quiver Dance and got Sucker Punch back, but that was not as significant as other updates.
The Overview of Bug-types:
As the dedicated worst type Bug-type is pretty okay. Due to its utility capabilities, it is not as terrible as Ice-type. But as a type that was designed to suck its adventures as a useful type were not exactly prolonged. Part of this was due to the fact that first time it became actually useful, Stealth Rock was introduced. However Bug-types sucked before Stealth Rock and will continue to suck in the future, because it is their destiny.
Bug-types are a fascinating concept for game design as a first-hand example of how to introduce a mechanic that was designed to be weak, how to improve it to for it to become fun and as a cautionary tale on how to not roll back a previously given buff. While Bug-types still have several type combinations to mess around with, due to Bug-type's curious status as a classification type(which forces it to become predominantly a primary type) and due to its status as the weakest type.
There is nothing that can improve this type really. All one can hope for more powerful Bug-types to be introduced and slowly be thrown away thanks to the power creep, because there are better Steel-types than Forretress and better Fighting-types than Heracross.