Exodus 10:14

וַיַּעַל הָאַרְבֶּה עַל כָּל אֶרֶץ מִצְרַיִם וַיָּנַח בְּכֹל גְּבוּל מִצְרָיִם כָּבֵד מְאֹד לְפָנָיו לֹא הָיָה כֵן אַרְבֶּה כָּמֹהוּ וְאַחֲרָיו לֹא יִהְיֶה כֵּן

The locusts went up over the whole land of Egypt and rested in all the borders of Egypt. They were very grievous; before them there were no such locusts, nor will there be after them.

This verse tells us that there will never be a locust swarm as bad as the one that hit Egypt before the Exodus but the Book of Joel (2:2) tells us of a swarm at that time that was unprecedented in its severity. How can we reconcile these two verses? Rashi explains that the swarm in the days of Joel was composed of several different types of locusts and its overall impact may have been harsher. The swarm in the time of Moshe was composed of only one species of locust; this was the phenomenon that will not be repeated.