In this case, it somewhat comes down to that whole "old school vibe" that Necromancer loves. Looking at my old copy of the 2nd Edition Monstrous Manual, it had six giant beetles and a grand thirty other insects, many of which made it into the first Tome of Horrors.I don't mean for this to come off as attacking the companies that put out these books. They're good books, but just have some weird consistencies.
Oh, and the 2EMM's insect entry contains the giant tick, which isn't an insect at all. I just noticed that.
What is it with giant intelligent plants always thirsting for blood? Ah well, the CR 6 bloodsuckle does at least have one creepy trick up its sleeve: mind-altering drug sap! Instead of waiting for new prey to come to it all the time, it injects sap into those it snares in an attempt to turn them into mind-slaves that are effectively cattle to the bloodsuckle, coming when called to provide more blood to sustain the freaky foliage.
Hm, two plants in a row. At least this one doesn't also suck blood! It is, however, absolutely weird. For starters, its appearance is that of a stump with a long, vaguely humanoid wooden hand protruding from it. If that alone wasn't enough to spark your "what the hell"-o-meter, bog creepers can actually swim and move across marsh territory without penalty, as well as sense any creature standing in the marsh with it within 60 feet. It can also spit out digestive acids, because why not? I guess if you ever said "hey, I need a CR 8 plant monster to face my characters, and they're in a swamp"...you still could have just used multiple shambling mounds instead of this thing. On the other hand, maybe some refluffing to make this creature some sort of demented relative to the shambling mound and tying their origins and/or habits together might make for some interesting story potential.
The first of several ports of creatures from Necromancer Games' hefty efreeti-themed title City of Brass, the giant brass men are CR 7 constructs that are specially built by the efreet to act as guardians and war machines. And war machines they can easily be, with an armament of huge metal fists, a built-in giant greatsword, and the ability to churn their innards to blast out molten brass at an opponent to deal fire damage. As if that wasn't bad enough, their golem-like magic immunity means that, when attacked by your spellcaster, they are only slowed by electricity and healed by fire. They are natives of the Elemental Plane of Fire, too, mind you; unless you're lucky, their very environment is likely to keep them going as nightmarish juggernauts coming to gut you like a pig. The lesson here: don't screw with the efreet, as they are vengeful and have giant brass constructs.