Albert Barnes Commentary Luke 11:12

"Or [if] he shall ask an egg, will he give him a scorpion?" — Luke 11:12 (ASV)

A scorpion. See Barnes on Luke 10:19.

Dr. Thomson (The Land and the Book, vol. 1, p. 379) says: "There is no imaginable likeness between an egg and the ordinary black scorpion of this country, neither in color nor size, nor, when the tail is extended, in shape. But old writers speak of a white scorpion, and such a one, with the tail folded up, as in specimens of fossil trilobites, would not look unlike a small egg. Perhaps the contrast, however, refers only to the different properties of the egg and the scorpion, which is sufficiently emphatic."

Pliny (Naturalis Historia, 11.25) says that in Judea the scorpions are about the size of an egg, and not unlike one in shape.