Food Critters

I have multiple instances of the same object- food- and several other objects- critters- that move to aforementioned food objects and destroy- eat- them on collision. The critters only chase the food if no solid objects are blocking the line of sight- they can see it- and otherwise continue their default random movement. The problem is, this only works for the first instance of a food object created. If this first instance is placed somewhere the critters cannot see it, any other food instance, even if placed in clear view, will not be actively followed by the critters.