Termagant
A Termagant (Gauntii virago) is the lowest Tyranid creature, disregarding Rippers. A Termagant requires numbers to be even borderline effective. A Termagant is nothing remarkable; it is simply a creature that exists to be killed. One saying goes "If your Termagants aren't dying, you're not playing Nids right". This is true. Generally, Termagants are only considered a threat to Guards and Orks. To MEQs they aren't even worth the time it takes to roll a die to confirm their death thanks to their light weapons and ineffective Chitin armour. Termagants on their own are not very good: making them so requires a unit of 30 (imagine them not so much as meat shields but as a meat wave).
In the fluff, a Termagant is a creature bred to drown opponents in bodies. They don't even have digestive tracts; they are expected to die in battle long before starvation could set in. A single Termagant is a cunning creature that will circle a foe, rather than a Hormagaunt's reckless headlong charge or Gargoyles' on/off attacks. Termagants will exploit weaknesses of any sort, and are canny in the regard as when to attack. Isolated from the Hive mind however they will flee, their instinct for self-preservation kicking in. Thus, years after a Tyranid invasion, Termagants are still found in caves, thick bushes, sewers, underground car-parks, tunnels, your attic, deserted warehouses, factory basements, your grandparents basement, your basement and the like. Where's that noise coming from? Which of course makes you wonder how they live that long without a digestive tract. Unless the hive fleet has a specialist guerilla strain that can …you know...live for longer than 48 hours. Termagants also instinctively attack any enemy that threaten Tyranid Warriors, the front-line synapse creatures of a Tyranid swarm. This would be somewhat common as lesser Tyranid creatures are commonly sacrificed as fodder for the preservation of the swarm, if it were not for a certain entry in their 5th edition codex that explains this behavior as a "deeper mystery". It has been speculated that this is an attempt for the termagant to get the warrior to notice him.
Using them
Termagants are cheap. Real cheap. As in "It'll take you half the game to justify the points shooting that special weapon at them" cheap (6th is out, they're even cheaper). They also die fast. Faster than even Eldar or Guardsmen. As such, take them in numbers. Though you can take them in groups of 10 to 30 you will find the smaller broods thinned out worryingly fast. This is in fact preferable to not having them shot because this means your other units are not being shot at. But there are a few tricks to using them.
- Alternate Take: Depending on your opponent, it may be worthwhile to take smaller-sized units. Against more elite forces, it makes them waste even more resources and time to wipe them out. You just need to make sure your synaptic net is strong (or you're using a Leviathan detachment).
First off, the Tervigon. Fielding Termagants makes them Troop choices (and they can secure objectives, which is good considering their toughness). They can also give your Termagants Feel No Pain (which is a good thing!) and make broods of 3d6 size for free. This means that you can drown your enemies in Termagants, who if needed can drag down surprisingly large things if they have to.
Secondly, the Deep Strike. The Gaunts can do this via Trygon tunnel. The issue with this is that they might just come on in the same turn as the Trygon and have to walk on from your table edge... and potentially run right back off again next turn if you don't get some Synapse to them that turn.
Devilgants
The Termagants have access to a number of weapons to slightly change their working on the battlefield.
The standard weapon is the Fleshborer, a weapon with decent firepower that can take down GEQs quite easily. It comes cheap, packs a punch and is iconic for the Termagants, making it a must-have for them.
Spinefists lack the punch that Fleshborers have. They're seriously bad. Being pistols, you can shoot while in combat, but if you're taking Termagants with the intention of hurling them into combat, just take Hormagaunts instead. They used to be a separate unit...for some reason, being called the Spinegaunt before some guy with common sense decided to roll them back into the Termagaunt family.
Devourers are very expensive to upgrade to, but they are very powerful. They pack a strong punch and are Assault 3, making for a maximum of 90 shots for a 30 strong brood. Situational, but they make it more painful to lose them and as such are worse fire magnets. In the new rules you can mix weapons in the brood, so it may be a good idea to give a few of them Devourers and shield them with Fleshborer/Spike Rifle (for the same range as the Devourers) guys.
The Spike Rifle trades strength and penetration in favor of range; not a very good trade since this turns them into single-shot Lasguns with 18" range. Skip it unless you want a mixed Devourer brood and you want the others to be able to fire at the same range.
The Strangleweb is worse than Spinefists. S2 but averaging 1 more shot with an 8" range. Seriously, is this a joke?
TL;DR 100 Gaunts on the field to shoot down, 100 Gaunts on the field, you shoot just one, then reload your gun, 99 Gaunts still alive to shoot dow- URK
Maximum Overspam
Yes, it is actually possible, it just takes numbers. Fill all your Troop choices with 30 Termagants. Now give them all Devourers. That totals to 540 attacks, averaging 135 wounds on T4 models and 90 wounds on T5 models. What can survive taking 135 saves? If you want to add more dice drowning, take 9 Carnifexes with two sets of twin linked Devourers with Brainleech Worms. That's another 12 attacks per model. That equals 36 per brood. And 108 in total. That's 648 all up. Then take 9 Zoanthropes for Synapse coverage. Then take 90 Gargoyles, two winged Hive Tyrants with twin linked Devourers and watch as you cannot fit all the dice on the board. 842 dice.
If you don't do this or something like this, use them for cheap ass canon fodder. Note that in any game with a points limit high enough to do this you'll get double FOC anyway. And remember to take Tervigons to smash metal bawkses and throw around more Synapse and powers and shit out free Gaunts. Six Tervigons doing this averages out to fifty four new Gaunts each turn until you start rolling doubles. And if you want more dakka, put spines on the Tervis and crushing claws for melee (plus one miasma cannon). Remember to take four Flyrants and give them all maximum Tyrant Guard (technically they don't need to follow the tyrant around) for twelve mini monstrous creatures.
This means you'll have nearly six hundred models on the table with more coming. And because you'll only ever see this in just for fun no points limit games you may as well just buy all the upgrades for everything for the lulz. Yes, aaaaaaaall the upgrades.
Only problem is that your opponent will probably see this coming and take all of the templates when they see you bringing out carrying case after carrying case or insist the game take place in your house. Still, they can only cover so much. Unless they're packing a Manticore Launcher Tank, in which case you are pretty much incomprehensibly fucked.
They can also be used with the endless swarm formation which at minimum requires you to take three broods of ten and can go up to ninety, backed by ninety hormagaunts and some warriors to keep them in synapse. Shooting them off the board means very little as they'll just enter ongoing reserves and respawn again if you roll well enough. Also they're superscoring. While not as popular as the Skyblight swarm which lets you bring more flyrants and crones and the more mobile gargoyles, it's a decent enough option for putting FoCless bodies on the field to steal objectives and camp them and stuff your opponent's face with dice. In the living tide formation which was arguably the first "formation of formations" list ever seen in 40k (though given the differences between it and the 7th edition formation of formation detachments it was likely a prototype for the concept) you have to take at least three endless swarms resulting in the hilarity of at least a hundred termagants on the field and potentially well over three hundred. Also they get to reroll their respawn rolls.