What senses do you think are involved in the location of food by hydra? By damselflies?

Hydra depends on tactile and chemical receptors to locate food. Some substances in the medium make the hydra expand their body. When a prey touches it, special cells in their tentacles called nematocysts capture the prey

Damselflies, on the other hand, rely on their sight for that purpose because they have sophisticated compound eyes and move freely using visual information.

Damselflies: Sight sense

Hydra: Touch sense

Explanation:

Adults damselflies use mostly the sight sense, although they can also use the smell sense, sometimes, when fiding prey. They feed mainly on small insects such as mosquitoes and flies which are resting among vegetation and grass, they find them using their vision. They catch the prey with the legs and bring it directly to the mouth.

Hydra, on the other hand, uses the touch sense. When hunting, they extend their tentacles leaving them floating around. If one of the tentacles touches a prey, a special cell called nematocyst secretes a stinging substance and the tentacle rapidly wraps around the prey and the other tentacles joint the attack, surrounding the prey and moving it to the mouth aperture.