Well, I hate ticks with a passion...but...
Dry ice is pretty expensive, and I suspect this will cost about a dollar per tick destroyed...
Alternatively, one can make
CO2 relatively cheaply with yeast and sugar
water in a 2 liter pop bottle. If you don't let them pile up the alcohol too far so it kills the yeast, you can use the yeast from the first batch to start a second and perhaps 3rd batch.
Here is a youtube example:
This would also have the desireable effect of produce low amounts of CO2 for longer periods of time.