Flea, lice. "Tick" is another possible answer, but ticks are actually arachnids, not insects.
it is a flea
gnat
flea
Wasp
Gnat - a small insect Goat - a four legged mammal
A frog? Maybe.
It could be either a pine ladybird or a harlequin ladybird.
Isle
A "bay" is a small protected body of water that is a four-letter word.
A four letter word for the noun brook is rill or a burn.
Spiv
Coal