Do ants sting or bite? I get this question a lot, and the answer I give is: “both–sometimes–it depends.” This is the kind of helpful answer that makes me near and dear to friends and family. So let’s break this topic down.
Most ants bite–or in other words they have mandibles (jaws) with which they can grab or pinch objects. However, many ants are too small to effectively bite humans. Ants are in the order Hymenoptera, and like their bee and wasp relatives, most female ants have venom and many have a stinger modified from the ovipositor (egg-laying structure). Thus, many ants both bite and sting.
For example, fire ants first bite, grabbing hold with their mandibles, and then sting repeatedly, injecting venom into their victim. This is why a quick swat at a biting fire ant can often remove them before they sting. Some very small ants, such as the fire ants’ tiny relatives the thief ants, have stingers too delicate to pierce human skin. On the other hand, some ants like leaf-cutter ants are so well adapted for biting that they no longer have a stinger.
However, not all ants with venom have stingers. Ants make use of a number of structures to spray, wipe, rub or otherwise dispense harmful chemicals. One prominent example is the formicine ants (Formicinae), a large sub-family of ants which make use of an acidopore to disperse venom. The acidopore is basically a round nozzle at the tip of the abdomen which ants use to spray formic acid. Many formicines have a ring of hairs surrounding the acidopore which can be used to help direct the spray.
Spraying formic acid is a very effective technique when used against many other arthropods and small animals, but generally goes completely unnoticed by humans. However, for the myrmecologist collecting ants with an aspirator, formicines are extremely noticeable, and suction collection is often followed by a cough. Inhaling formic acid is not fun.