Well, for starters, I'd change the PIC. 16F84 has no ADC, so there's little way to read that analog value (unless you try the capacitative one, which IMO takes a lot of cycles). 16F628 is the direct, cheaper, replacment. If you're much into pics, go with 16F877A. If not, just switch to AVR.
Next, I'd start using that IC to get a signal from my sensor. What language are you using? Some have a very easy learn curve, while beeing inefficient overall (oshonsoft pic compiler for example, allows you to do an adc reading with a single instruction). Others implement a standardised langauge (such as C) and thus make it harder for you to do a reading (actually, you have to read the datasheet, to find out how it's made), but allow a great deal of flexibility.
Generating a servo signal is easy, I assume you've already done that, since you can already move your insect (personally, I'd like to see it, since I'm a big fan of multilegged stuff). All that's left now is integrating the ADC value over a period of time, to reduce noise, and use that figure to drive some logic. This logic will then create motion profiles and actuate them in the servo/servos
