what can I substitute for pill bugs?
What kind of time frame are you working with?
I usually send some of my more outdoor-sy kids on a mission - -they usually come back with a pile of them. If the weather has you beat, then I'm not sure, but lady bugs might work if they didn't fly off. Pretty much any terrestrial bug that moves would be a substitute.
The concept is that Animals respond instinctively to stimulus and changes in their surroundings. You could conceivably use any animal to demonstrate this concept. A horse in a round pen comes to my mind when I think of responding instinctively to stimulus and changes. It's all in what resources you have available.
The key is that the students develop an understanding of the concept -- the road to that end can be up to you.
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