Oh I agree it is a very very common misconception even I only realized after watching the film half a hundred times.Uh, those don't look that dissimilar to each other. They appear far closer than the Chariot bugs look to any of the other Arachnid castes. The fact that few, if any, Arachnid casts actually look like they belong to the same species or even related species but instead seem to be random anthropoids slotted into a given role further lends credence to the idea rather than distracts from it. Why do they all look so different? Because they all were different species from different worlds until the Arachnids assimilated them.
And I will note you yourself commented on how it was a "common misconception" to assume both bugs were one and the same so the differences can't be that massive.
But they do have distinct shapes, angles, and colors. Brown vs Red, flat top vs curved top, etc.
The bugs, a race which has no technology of any kind can pinpoint snipe a city from across the galaxy WITH A ROCK, despite countless defences and early warning systems in between the two empires?...Unlikely.If we ignore Buenos Aires and the destruction of zegema beach in Starship troopers, Behemecoatyl desire to destroy humanity in Starship Trooper 3, Trig's destroyed home town in Starship Troopers invasion, the apparently common occurrence of Arachnid spores seeding Federation worlds in Starship Troopers Traitors of Mars. The Bugs have always been portrayed as hyperaggressive monsters obsessed with wiping out humanity.
Also ST2 and ST3 are the results of writers/producers not understanding the first film, predictably they go with the very literal interpretation of a propaganda film.
Everything you see the Federation do is from a slanted angle, Arachnids have been known for quite sometime (maybe even tens of years) and judging from all the maimed adults/old people they've fought them before. The Federation need somebody to punch to keep their act together, bugs are just a great way to have a war.In contrast we see the Federation actively tries to avoid war with the Arachnids establishing a quarantine zone for the Arachnid empire to inhabit and colonize and even the state approved media openly questioning on the eve of war if a "Live and let live" approach was better than invading Klendathu.
They are aware the bugs can colonize other planets, but judging from how effective their anti-space weapons are (blindly launching crap into space and praying the federation are stupid enough to ram into it), I doubt their colonizing abilities are especially fast or efficient.Eh chalk it up to scifi writers have no sense of scale or the Bugs are more capable than the Federation at the time suspected. Which makes sense since they didn't even seem to believe the Arachnids were intelligent before the Bug War.