From the Borderlands Wiki : Shotguns work well against Spiderants, not only because they can easily disorient, but also because follow-up blasts to the abdomen can usually take down even the toughest specimen.
The larger varieties of Spiderant, particularly Badasses, are also much harder to disorient by comparison to their smaller counterparts or even when compared to the optional bosses.
A solution is to focus the targeting element on the upper fringe of the armored head while backpedaling.
Due to a collision detection quirk involving their walk animation, several of these shots will register as abdomen hits, dealing critical damage from the front even though the abdomen itself is not truly exposed.
A player with a good elemental (preferably corrosive, due to its long DoT duration) weapon can keep a spiderant completely defenseless as they stagger and are open to abdomen attacks.
This is also one of the only reliable ways of staggering a "Badass" Spiderant Essentially, shots aimed high may count as critical hits, and an elemental attribute to your weapon can only help.
gaming.stackexchange.com/users/1777/Keaanu
I usually drive over the bastards as much as possible.
gaming.stackexchange.com/users/2198/Alan B
I generally swap to a high capacity SMG and fire off bursts of shots while strafing/backpeddling.
The reason for the burst firing is to get the disorienting shots to trigger so they turn.
If they don't, just keep burst firing.
Once they've turned their abdomen is wide open and you can unload the rest of the clip for almost 100% critical shots against the spiderants.
gaming.stackexchange.com/users/7639/Sorean
I always relied on elemental damage to kill them, using either corrosive or fire damage to do a bulk of the work.
That has worked for me with a Siren or Soldier.
With SMGs and Assault Rifles, you tend to get abdomen shots occasionally while circle strafing, even when it isn't stunned, which also helps.
As a Hunter, I'd try and rely on pistols with 3x or 4x elemental component (Defiler comes to mind), and let the DoT do the damage.
This will prevent you from dumping all of your ammo into them.
gaming.stackexchange.com/users/15571/Don Sealy
To add to Keaanu's answer, since you're playing as a hunter, using a masher revolver instead of a shotgun might be a good idea.
The skills in the gunslinger tree, especially gun crazy, can help make up for the lack of an element on mashers and you've probably got decent revolver proficiency bonuses built up by now too.
gaming.stackexchange.com/users/7992/Fambida
If you wish to take out "the big ones" with ease, you should aim for the abdomen as much as you can.
This is easy to do at range, as long as you get the timing right.
Keep them at a distance, and get them to use their ranged attack.
When they do this they hug the ground, while pushing up their abdomen, making the Critacal Spot an easy target.
You can also kill them with a SMG "Anarchy" because as it says on the wiki: "The Anarchy SMG fires a spray of four projectiles per shot at the expense of two rounds from the magazine.
This effect essentially turns the SMG into a high-speed Shotgun that is able to throw up a "wall of flak" I'm a soldier myself, and have taken out just about everything with my Double Anarchy (Even the Badass versions) Hope that helps
gaming.stackexchange.com/users/25165/Gareth Jones
I've found that things like explosive SMGs have been very effective for me.
It seems to me that the abdomens of spiderants seem to have extra vulnerability to explosive damage.
gaming.stackexchange.com/users/9300/CyberSkull
I always carry a back up corrosive weapon, and I suggest you make one or two part of your loadout.
The game itself states you should use corrosive weapons for armored enemies like Spiderants and Alpha Skags.
The best thing for them is a corrosive shotgun.
Because of the spread shot it will hit the abdomen or belly when not directly aiming there.
Or, if you prefer a bit more accuracy, a corrosive revolver or sniper will make short work of them.
gaming.stackexchange.com/users/50533/DeathDealer
How do you deal with big spiderants?  They take basically no damage unless you hit them in the abdomen. And the big ones are hard to disorient. I'm playing hunter, so sniper rifles and revolvers are my most used guns.
How do you defeat big spiderants?
gaming.stackexchange.com
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gaming.stackexchange.com/questions/30615
gaming.stackexchange.com/users/2771/Šimon Tóth
Shotgunswork well against spiderants. You can also use a masher revolver and carry a back up corrosive weapon. Several types of weapons are suggested as legitimate options.
Shotguns, SMG, corrosive or fire weapons, masher revolver could defeat big spiderants.