Verses 18-19 describe the two major world powers of Isaiah’s time as plagues of insects. Yahweh will cause them to punish his people. The figurative use of flies and bees needs to be understood as referring to enemy armies. From verse 20 onward the Assyrians will be in focus. The mention of two quite separate geographical locations, Egypt and Assyria, may suggest that Yahweh is about to bring enemies from everywhere. However, why Egypt is mentioned in the present context is not quite clear.

In that day is the standard prophetic phrase used as a reference to some future but nonspecific time. It is related to the events that have just been described in the previous verses. The phrase occurs more than forty times in the book of Isaiah (see, for example, 2.11, 20; 3.18; 4.2). It may be rendered “When that happens” or “At that time.” It should not be confused with the New Testament concept of “the last day” (for example, John 6.39-40); it merely refers to some future moment, usually not far into the future.

The LORD will whistle: This imagery is rarely found in the Old Testament. It occurs here and in 5.26 (see the comments there). The Hebrew verb rendered whistle is used in Ezek 27.36 and Zeph 2.15 with the sense of “hissing,” probably as a gesture of disgust or condemnation. Its basic meaning here is to signal (see Good News Translation) or call, and it implies that Yahweh is calling someone to come. This verb has two object clauses (for the fly … and for the bee …). Some languages may require that the verb be repeated before the second clause, the one concerning the Assyrians.

For the fly which is at the sources of the streams of Egypt: The fly is an insect pest. Here it is a figure for the enemy army of Egypt. Contemporary English Version makes this clear by saying “and armies will come from Egypt like flies.” Translators need to decide whether the figure of the fly should be kept without further clarification, or whether the meaning of this figure should be made explicit as in Contemporary English Version.

At the sources of the streams of Egypt is literally “at ends of the streams [or, rivers] of Egypt.” This seems to refer to the places from which the rivers begin to flow, which is the region of the Upper Nile River. Revised English Bible and New Jerusalem Bible both have “from the distant streams of Egypt.” However, Bible en français courant and Die Bibel im heutigen Deutsch refer explicitly to where the Nile River ends in the Mediterranean Sea. Bible en français courant has “in the delta of the Nile,” while Die Bibel im heutigen Deutsch says “at the mouth of the Nile.” Since it is not clear whether this phrase refers to the source or the end of the river, it may be best to say “in the region of the Nile River,” as in the Septuagint.

Egypt was one of the great civilizations of the ancient world, centered around the Nile River in northeast Africa. It played an important role in Israel’s history, already beginning with Abraham.

And for the bee which is in the land of Assyria: The bee is another troublesome insect, one that stings moreover. Here it is a figure for the Assyrian army. The structure of this clause is parallel to that of the previous one. Contemporary English Version completes its sentence (see above) with “… and from Assyria like bees.”

Translation examples for this verse are:

• At that time Yahweh will signal for the Egyptian army to come like flies from the Nile region [or, the land of the Nile] and for Assyria’s army to come like bees.

• At that time Yahweh will signal for the fly at the head of the Nile River in Egypt, and call for the bee in Assyria.

• In that future time Yahweh will whistle for the fly at the mouth of Egypt’s Nile River and for the bee in the land of Assyria to come.

Quoted with permission from Ogden, Graham S. and Sterk, Jan. A Handbook on Isaiah. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here .