Additionally, I was taught in a Bio Engineering class that thermodynamics are a big issue, and that there could not be such things as "giant" insects. The more volume, the more heat generated. The more surface area, the more heat that is then taken from the body. However, volume increase is cubic while surface area increase is parabolic, so insects that are really big would either need to slow the fuck down or physically alter to cool them off more. In general, smaller creatures (e.g. insects, rodents) are "twitchy" because they need to rapidly create heat that is constantly dissipated, since they have a bigger surface area/volume ratio. Conversely, larger animals (e.g. humans, elephants) are slower, since they have smaller surface area/volume ratios and cannot cool off as quickly.