hehe, funny you mention the raid on the Skinny's City, that was the only thing I remembered as well, beyond the fact that they hated fighting bugs the most...
I think the best way to sum up the bugs is to quote a bit from
Space Cadet. In
Space Cadet they have the Venusian people who are basically giant amphibians that live in a purely matriarchal society due to the fact that they have very few males and they're small/diminutive. In addition they live very simple lives, using almost no machinery, and making their dwellings out of the simplest materials. Spoiler alert, at one point they realize that the Venusians are capable of synthesizing any comprehensible chemical with no difficulty what-so-ever. The Texan of the group put it bluntly saying
"These little guys have forgotten more about chemistry than any of us or our ancestors have ever known. We shouldina assumed just 'cause they seem primitive ta us that they are."The bugs know more about biology than we'll ever know. This means that they can create increasing powerful creatures with bio-acids, natural electric impulses ALA Electric Eels, Projectile Needle-like apendages, etc. that can penetrate Mobile Infantry (M.I.) Combat Suits or at least gradually wear it down over time.
The other advantage they had was the ability to produce truly massive amounts of footsoldiers and workers. In short: They used the infamous proposed "Fireboat" tactic (Having a large group of lightly armored craft with extremely heavy weaponry capable of hurting a ship at least two times the size). If all it takes is one shot to hurt, disable, or destroy a Combat Suit, then all they need to do is have a single one of their soldiers get close enough. Thus they send in forces that outnumber their enemy 12 to 1 at the very least.
The big issue, on top of everything, as Heinlein made sure to point out to the reader, is that only by killing a "Brain Bug" (think Hive Tyrant or other synapse beast with Tyranids) or a "Hive Queen" (Norn Queen for Tyranids) do you actually do any damage to the swarm. He then pointed out that, in about twenty years of war, the bugs had killed hundreds of thousands of troops, while the M.I. had only managed to kill about 16 brain bugs.
Interesting, Heinlein was astute enough to realize that a biological enemy could be fought well with biological weapons, which were used in massive quantities to great effect against the bugs. Though Heinlein, again, makes sure to point out that the bugs never had their warriors/workers/etc. evolve resistances to these biological weapons, because they weren't permanently damaging (diffusion) and the loss of anywhere from 100-1,000 of them was a Stalinesque "Meh" moment.
Interestingly, if you read
Space Cadet Heinlein *VERY MUCH* puts down the marines he built up so much in
Starship Troopers and makes a comment about how future wars among humans and humanoid creatures will require troops trained in diplomacy, sociology, religion, and psychology (irony how right he was there

).