Toxn

I've eaten ants by accident. Left a soda can out at dark, came back to take a swig of some Coca Cola and a healthy serving of ants along with it. 

 

Ants seem like a viable protein source for regions that find it unfeasible to have beef or pork, much lower energy needed to sustain ant populations. I would totally eat a good antburger. 

As mentioned: formic acid. Not good stuff in large quantities.

Also ant-related: my third-favourite toxin! Oh ponerotoxin, you induce such long-lasting agony...