JimG. said:Anything that masks carbon dioxide...that's what they zero in on.
Amusing anecdote...
Last year I brought a cooler of ice cream, packed in dry ice, up to a BBQ in the Whites. Besides learning that the net result were a whole bunch of ice-cream-flavored *rocks* that needed desperately to thaw before being eaten, the cooler's vent spout attracted every blackfly and mosquito in the area.
It was quite the site, all the bugs gathered around the spewing CO2.