(2) There are five food chains in the picture: grass → herbivorous insects → spiders → insect-eating birds; Grass → herbivorous insects → spiders → frogs → snakes; Grass → herbivorous insects → insect-eating birds; Grass → herbivorous insects → frogs → snakes; Grass → mouse → snake. The longest food chain among these five food chains is grass → herbivorous insects → spiders → frogs → snakes.
(3) From the above food chain, it can be seen that if people catch a large number of birds and frogs, spiders and herbivores will lose the control of their natural enemies, which will lead to an increase in the number of spiders and herbivores and destroy the ecological balance.
(4) Congenital behavior refers to the behavior that animals are born with and determined by genetic materials in their bodies, which is necessary to maintain the most basic survival, while learning behavior refers to the behavior obtained from life experience and learning through the role of environmental factors on the basis of genetic factors. The behavior of frogs preying on insects belongs to innate behavior.
So the answer is: (1) Is there a ridge? (2? )5; (3) Grass → herbivores → spiders → frogs → snakes; (4) Spiders and herbivores; (5) congenital behavior.