leave the ants alone.
Besides it being an archaic way of going about getting what you need, you have to contend with separating your microgram quantities of formic acid from ant nucleic acids, lipids, and whatever else there is in ant blood mixed with squished ant. And you can bet that there is a fair amount of formates in that as the formic acid reacts with everything it can when you squish the ant.
UTFSE. Make it from ethanol and Ca(ClO)2.
See Post 92035 (https://www.thevespiary.org/talk/index.php?topic=5108.msg9203500#msg9203500)
(CHEM GUY: "Re: Home Made Chloroform and Iodoform", Chemicals & Equipment). -Probably worth reading that whole thread.