Zapper turrets are one of the most useful support turrets. Zapper turrets slow down enemies and can stun them as well, with a maxed zapper turret being able to stun 30% of the time. They fire quickly and have good range, yet low damage. Upgrading increases range, chance to stun, and damage.
A Zapper can drastically increase the amount of damage your heroes and other turrets can put out, as well as stunning enemies on your trail. This makes them highly recommended, at least for beginners. On more confined maps like kitchen, Zappers are preferable, on more open maps where grubs are everywhere (such as Yard, Attic or Garden), the Force Field turret is suggested instead. A maxed out Zapper turret will slow down groups of enemies, and stun many of them as well.
Although Forcefield Turret is recommended for open maps, zappers can still be useful. One of the big advantages is that they can also help you fight with other bugs if you come near your base. They are also very useful for getting rid of baby spiders, because of their small AoE.