Carbon dioxide snow ("dry ice" snow) is very cold, about -78ºC (-108ºF). But being cold does not necessarily mean being able to cool. Or, put another way: big temperature difference is not the same as high energy transfer.

The snow that is produced by a fire extinguisher, has of course another goal than freezing tiny bugs. It is therefore of a very different quality. Compared to Cryonite snow, the particle size is big, and the particle speed is slow. Regarding killing bugs, it simply cannot get the work done. (We might as well admit here that Cryonite is a lousy fire extinguisher).

The Cryonite effect - the rapid freezing - is dependent on a certain mix of particle sizes and speeds.

The cooling occurs in several phases, where each phase has an optimal combination of a particle size and speed, for attaining maximum cooling rate.

Having somewhat bigger particles in the mix, makes the particle-stream efficacious also at longer ranges, and in warmer surroundings.

The speed helps the penetration deep into thin cracks and crevices, in buildings as well as in machines, and also hurtles them through long pipes.

But the speed is also an integral part of the freezing itself.

For the energy transfer to be efficient, the ice-particles need good contact with the target (bug or surface). A high speed makes for a good, contact-making impact on the target.

For a more detailed explanation, see "The Cryonite effect - extended" (pdf), Click Here