flea bite vs insect bite

flea bite and insect bite both are nouns.

Word	Noun	Adjective	Verb	Adverb
flea bite	Yes	No	No	No
insect bite	Yes	No	No	No

As nouns, insect bite is a hypernym of flea bite; that is, insect bite is a word with a broader meaning than flea bite:

flea bite: sting inflicted by a flea
insect bite: a painful wound caused by the thrust of an insect's stinger into skin

Other hypernyms of flea bite include bite, sting.

flea bite (noun)	insect bite (noun)
a very minor inconvenience	a painful wound caused by the thrust of an insect's stinger into skin
sting inflicted by a flea