In these verses there is an evident allusion to the idolatrous
   worship in Egypt.  Among the Egyptians, almost everything in
   nature was the object of their idolatry; among beasts were
   oxen, heifers, sheep, goats, lions, dogs, monkeys, and cats;
   among birds, the ibis, crane, and hawk; among reptiles, the
   crocodile, serpents, frogs, flies, and beetles; all the fish
   of the Nile, and the Nile itself; besides the sun, moon,
   planets, stars, fire, light, air, darkness, and night.  These
   are all included in the very circumstantial prohibition in the
   text, and very forcibly in the general terms of Ex 20:4, the
   reason of which prohibition becomes self-evident, when the
   various objects of Egyptian idolatry are considered.

  Ro 1:23