All Bikers Are Hells Angels: By the third book, depraved biker gangs are a problem in areas where neither the US government or the Chtorrans have too much presence. Especially when they have rocket launchers on their bikes.
Arbitrary Skepticism: Most people don't believe in the Chtorrans until the worms start moving into towns and eating people. Even then the Fourth World Alliance insists on downplaying the invasion, until a captive worm escapesis let loose and starts chomping its way through their delegates.
Armies Are Evil: Averted in that the protagonist is both soldier and scientist and can therefore see both arguments (the scientists want to study the alien invaders, but that means allowing their ecology to gain enough of a foothold to understand how it works. The military want to burn the Chtorr before they can get a foothold, but this approach is inherently flawed, as without better knowledge of the Chtorr the war is hopeless anyway). He's not alone in this viewpoint, but it just tends to make the shouting matches even more confusing.
Back from the Dead: Uncle Ira. Being dead is a great way to keep people from spying on you.
Bad Ass: Subverted in "A Season for Slaughter", when McCarthy's badass takedown of an arrogant major has serious consequences both political and personal. Obstructive Bureaucrats are just as much a threat to the war effort as the man-eating worms.
Batman Gambit: Standard Operating Procedure for both the Uncle Ira Group and the President of the United States.
There are clues that there are no individual species per se in the Chtorran ecosystem - just the ecosystem itself - with a vast web of what we would consider "different species" that are genetically compatible for breeding.
Brainwashed: In "A Rage for Revenge" McCarthy is captured by renegades (humans who worship and help the Chtorr) and is converted to their cause by charismatic cult leader Jason Delandro. This story is intermingled with flash-forward chapters detailing McCarthy's participation in the Mode Training, which some critics believe to be a form of government brainwashing. Gerrold based Mode Training on est a.k.a. Landmark Education.
Death from Above: Lizard dishes this out on several occasions. And in an interesting twist, a group of renegades setting up a night ambush are exposed to a counter-ambush when an orbiting solar mirror is suddenly turned on the area.
Death World. The original planet of the invaders is assumed to be like this, and they're eager to make Earth just like it.
Depopulation Bomb: The human race is decimated (as in the pop culture version not the Roman version; reduced not by one tenth its former number, but to one tenth) by the plagues before the alien locusts show up.
The End of the World as We Know It. Implicit. If the war is won, it won't be in the lifetime of any of the characters. Best case scenario? If everybody got a clue all at onceduring the first book, the Chtorr would be beaten in fifty years. "Every day that passes without a program of unified resistance to the Chtorran invasion pushes the window of possible victory two weeks farther away." Worst case scenario? "We could all be dead in ten."
Epigraph. Ranging from newspaper articles and quotes by Solomon Short (a newspaper columnist) in the first two books, limericks in the third book, and long quotes from The Red Book in the fourth.
Genius Loci: The Chtorran cities, possibly the entire invading ecology.
Got Volunteered: Subverted on a number of occasions — it's made clear that there are legal precedents involving the use of soldiers on dangerous missions. In the first novel Duke Anderson tells McCarthy he does have the option of refusing to go on a dangerous mission, but then he'll be on the first chopper out of here because a soldier who won't take risks is useless to him.
Government Conspiracy: Every move by the United States government to fight the Chtorrans is viewed by the rest of the world as an attempt to reassert American supremacy. Ironically these suspicions would be all-too-accurate under different circumstances. The best example would be that every single freaking computer chip the US has built since their deposition as a global superpower is in fact a Trojan Horse; each one has a Tracking Device and a Self-Destruct Mechanism - they know where all the weapons on earth are, and can destroy them at any time. As one character put it: "There's enough history between us to fuel a major war, and if it weren't for the convenient intervention of the worms, that's probably what we'd be doing right now."
Okay, the Uncle Ira conspiracy must be stated in full to be believed. It begins when a periodic Gulf War escalates into a reverse Cuban Missile Crisis. The Third World then gets its act together for five seconds and demands that the US stand down or get nuked. The President at the time submits rather than start World War III, and the US is forced to disband its military and make multibillion-dollar reparations. This is when the conspiracy is hatched; pretend to obey, and in ways that benefit the US secretly. Instead of sending money, they send food and machines, forcing US industries to be redesigned to meet those demands. The US suffers a short depression, but loads of super-technology is developed in the process, causing an economic boom despite the treaties, and making the world even more dependent on US technology (complete with the aforementioned Trojan Horse chips). Space technology is developed, to supply the Third World with energy from solar-power satellites - requiring US expertise to maintain, and enabling them to develop space; thanks to a lunar colony, they have mass drivers. And half a million teachers are sent into the Third World to bring them up to speed; and teach them American values.
The Great Politics Mess-Up: Narrowly averted. (Early printings of the books contained references to the Soviet Union still existing in the future. Later ones, not so much.)
Hide Your Gays. Very much averted. McCarthy is bisexual, and there are several other gay characters (although homophobia is also present). The author even subverts his own work through Randy Dannenfelser who is the personification of every negative gay stereotype in existence.
Hive Mind: The Telepathy Corps, and probably the Chtorran ecology itself.
Hollywood Science. Averted as the Chtorran ecology was designed in large part by British reproductive biologist Jack Cohen.
Hopeless War: Things are not going well, everybody knows it and acts accordingly.
Humans Are Special: Then again, the books make it clear that Earth's native ecosystem is all but helpless against the Chtorran invaders, leaving human sentience as the only thing that could possibly overcome them.
Idiosyncratic Episode Naming: Each novel has a name of the form "A [X] for [Y]" where the words X and Y are alliterative. "A Matter for Men", "A Day for Damnation", "A Season for Slaughter" and "A Rage for Revenge." Forthcoming books will be named "A Method for Madness", "A Time for Treason" and "A Case for Courage", according to Word of God.
In That Order: One particular quote- "Life is short. Then you die. Then the worms eat you. Be grateful it happens in that order."
It Can Think: Inverted, as all the evidence of the Alien Invasion is that there must be an intelligence behind it, yet there's no sign of spaceships or any other means of crossing intersteller distances. The Chtorran gastropedes are assumed to be behind things, yet their intelligence is that of the idiot savant — they're very good at opening locks and can somehow communicate over distances, yet little else. The series appears to be implying that the entire Chtorran ecology is some form of group mind.
Jerk Ass: McCarthy according to everyone he meets. IRL, most asocial geeks really like him, however. Also his friend Ted, and Randy Dannenfelser, aide-de-camp to General Wainright.
Though some would judge McCarthy a Jerk with a Heart of Gold. As abrasive as he is to others, he is incredibly self-destructive because he hates seeing anyone get hurt. Then again, he also executes a renegade who is pregnant with his child because she fed his adoptive children to worms. (McCarthy is a complicated man.)
Justified in that after the initial plagues and population crash, everyone on Earth has a screw or two loose and may exhibit ... unpredictable behaviour. See above re: Dysfunction Junction.
In the short story Enterprise Fish, someone accuses McCarthy of being Not Himself, but changes his mind when he delivers a Bond One-Liner after watching another Jerk Ass get swallowed whole.
Karmic Death: The first novel begins with a newspaper article on how a sheriff had fired two volunteers searching for a missing girl, because they claimed to have seen 'Chtorrans'. The novel ends with an article stating the same sheriff had gone missing during the evacuation of her town due to the Chtorran threat.
Technically everything. No matter how harmless, or relatively harmless, it looks, it can probably kill you. Early in the first book, oneofthe soldiers gets his finger bitten off by a Chtorran millipede. Losing the finger didn't kill him, it was the multiple infections caused by the alien microorganisms that were transferred by the bite that did. Cotton Candy plants look like Exactly What It Says on the Tin. It's not until they go through a massive "bloom" and throw clouds of pink, sticky filamentous goo all over everything that the problems start: massive destruction of neighboring ecosystems, gooping up machinery (rain just makes it stickier), oh and incidentally causing humans who inhale the dust clouds to cough their lungs out in bloody chunks.
Kill It with Fire: Flamethrowers are the only reliable way of stopping a charging worm, as their alien physiology makes them Immune to Bullets. The protagonist has also used cold-gas weapons when necessary, but doesn't prefer them.
Reassigned to Antarctica. McCarthy begins "A Rage for Revenge" working on a plague reclamation unit, thanks to the disastrous end of the previous novel.
Roaring Rampage of Revenge: When Jason Delandro's cult kills McCarthy's adopted children during an attack, he raises a scratch force from a unit of rear echelon personnel, tracks down their hideout and wipes them out except for a few prisoners whom he tries before a Kangaroo Court and then personally executes. One of the women turns out to be bearing his unborn child. McCarthy shoots her anyway. "My kids are dead; why should I give a fuck about yours?"
Rock Beats Laser. The invading ecology uses no weapons (though the Chtorr-worshipping renegades do) but even its most innocuous forms can be deadly, as seen when the 'cotton candy plant' creates huge duststorms that knock helicopters out of the sky, explode like grain silos, and cause thousands of deaths by clogging up people's lungs.
Self Fulfilling Prophecy: Shorty instructs McCarthy in the use of a flamethrower and tells him to burn a Chtorran worm even if someone else is in the way. Guess what happens to Shorty on the next mission...
Shoot the Dog: The very first chapter has Duke Anderson shoot dead a little girl so she won't be eaten alive by Chtorrans. Things go downhill from there. In fact the entire war consists of Shoot The Dog moments, considering that the survival of the human race is at stake.
The Squad: Siegal's team in "A Season for Slaughter".
The Squadette. Averted by the second book; due to universal conscription, unisex combat teams are completely normal.
Starfish Aliens: The main point is that the aliens are very alien and one ongoing plot point is trying to discover whether or not there is a guiding intelligence behind the invasion at all. So far the jury is out.
Stock Shticks: What does a Chtorran call a liberal? Politically Correct lunch. What does a Chtorran call a conservative? Gunpowder-seasoned lunch. Create your own Chtorran Joke: What does a Chtorran call _______? Lunch!
There Is No Kill Like Overkill: Subverted in that whatever overwhelming force is used against the Chtorran ecology only helps it bounce back stronger because the local Earth ecology has now been sterilized.
Trilogy Creep: Gerrold specifically calls it "The longest trilogy I've ever written."
The Neidermeyer: Major Bellus. Averted in McCarthy's case — as a newly-minted officer he starts throwing his weight around, only to have it pointed out that his job is to inspire people, not act like a jerk.
Uriah Gambit: After humiliating an idiot officer assigned to him, Captain McCarthy goes on a mission to investigate some Man Eating Plants, only to find he's being denied technical support, his security team has been ordered to withdraw without telling him, and there's a massive duststorm coming up that no-one's warned them about. He's finally extracted by a mysterious benefactor, but loses several members of his team in the process.
Ultimate Job Security: The Uncle Ira Group protects McCarthy despite him committing several acts liable for court martial; partly because he's good at his job, but also because McCarthy's habit of causing disruption can be turned to their political advantage. He still has to deal with the occasional Obstructive Bureaucrat attempting to kill him - to the point that they really don't care if they kill other soldiers in the process.
Vaporware: Book 5, so far. A particularly tragic example of vaporware, as the last book ended on a cliffhanger.
Vichy Earth: Opinions differ (in the case of renegades, often violently) over whether humanity should follow a policy of resistance or co-existence with the Chtorr.
The official GURPS campaign setting suggests that the bunnymen and libbits may be what's left of a previously invaded race that opted for the latter. Given that they're essentially at the bottom of the "natural" Chtorran food chain and absolutely thrilled about it, it isn't considered to bode well for the fate of humanity if it also takes this route.
Walk This Way: McCarthy is saddled with Major Bellus who accidentally walks near a grove of shambler trees: Man Eating Plants hosting an entire ecology of carnivorous symbiotes that swarm when they sense the vibrations of nearby prey. McCarthy points out that these vibrations are relayed by the creeper vines lying all around them, and the only way not to trigger them is to walk out of range at five meters per hour. Cue a Silly Walk that (as McCarthy enjoys pointing out to Bellus) is being relayed via cameras to an extensive internet audience hoping they'll die in an interesting and horrible fashion. Eventually Bellus breaks down under the strain and begs for his life, so to conclude this Humiliation Conga McCarthy walks out normally, saying they were never in any danger as the shambler grove was uninhabited. This stunt destroys Bellus career; unfortunately it also earns McCarthy the ire of his superiors who try to get rid of him with an Uriah Gambit.
When Trees Attack: ...the only way to survive is somehow walk out of range at five meters an hour.
Yanks with Tanks: Subverted in that the United States was made to decommission much of its military after losing a war in Pakistan. Ironically this now makes the USA the most powerful nation on Earth, as its armed forces were not mobilized to deal with the plagues and so survived mostly intact.
Zeerust: Averted mainly because the author shows not only technological changes but social changes as well. There is a noticable emphasis on internet/cyber-related technology in "A Season for Slaughter" (1993), but as similar devices were used in previous books it doesn't seem unusual.