the tympanum
they use their eyes
Thorax
the thorax
Its exoskeleton.
their eyes
The head and the thorax of insects are the two body parts that are smaller than the much larger abdomens that accommodate internal structures necessary for the equivalents of breathing, digesting and reproducing. The head, as the first part, contains the components necessary for eating and sensing. The thorax, as the second part, is compared to an engine or motor because of its support to legs and wings.
The archerfish primarily spits water from its mouth to catch insects above the water's surface. Its specialized mouth and tongue are adapted for forming a jet of water to shoot down prey.
Abdomen
It is the tongue.
Insects have three body parts, Head, Thorax and Abdomen. I therefore believe Thorax is the correct answer to your question.
The body part that insects have and cat fleas do not is wings. Fleas are wingless insects that feed on the blood of animals including cats.
The heart is a common part of the body that is found in snakes and insects. Eyes are another common feature between insects and snakes.