Common elements: Dragonflies usually don't live long enough to develop an affinity, but when they do it's typically Air, Poison or Acid.
Hereditary magic: It is unsure whether affinities are passed down or if they come from the environment due to them taking so long to surface. It's highly likely it is a mixture of both!
Poison/Acid: Dragonflies thrive on toxicity, so they are highly resistant to these elements.
Water: They cannot swim by any means, and are very easy to drown. Most traps are water based, a common trick is to use sweetened water.
Common locations: Pretty much everywhere. During the winter months they're mostly only found near waste dumps and in Deep Mountain, but they start appearing everywhere once the weather heats up.
In particularly hot and humid places, it's generally smart to keep food covered.
Climate preferences: They're particularly fond of dank and putrid environments like swamps, however hot and humid places are another winner.
Things decay quicker in places like that, after all, and who'd want to eat anything that's not rotting?
Level of intelligence: Dragonflies are not intelligent, they are extremely easy to trick and trap and are unable to think for themselves.
There are, however, rumours of highly intelligent dragonflies in Heaven's Keys, and the giant dragonflies in Deep Mountain are thought to be smarter than others.
Language: They do not speak any tongues, and they do not appear to communicate with each other.
This may not be the case for those in Heaven's Keys, but honestly who even wants to go find out? Not me, that's for sure.
Trivia: These guys are honestly never good news. Their bites hurt and easily become infected, they can carry nasty viruses, and they always occupancy bad smells. Gross.
Decaying corpses have a sickening sweet scent, so any kind of sweet smell is appealing to dragonflies. Use this to your advantage, and make yourself some traps. Or go buy some, whatever. Just keep them off your food, cause they'll make you mighty sick if they touch any of it!
That said, nobody hates these guys more than Hanged Men. It's no doubt hard enough keeping corpses fresh in the summer months, and these guys don't make it any easier. Hanged Men probably smell like walking snacks, and they certainly treat them like that! If you ever need bug repellent tips, I'm sure they're full of them.
Love the play on words and the concept.