Coastal areas bordering the Red Sea remain under “serious” threat from desert locusts, with small swarms likely to form, while numbers of the insects fell in Africa’s Sahel region, the United Nations said.

Immature locusts known as hoppers formed bands in Egypt, Sudan and Saudi Arabia, and breeding is expected to continue, the UN’s Rome-based Food & Agriculture Organization wrote in a Jan. 4 report on its Locust Watch website.

Adult desert locusts can eat their own weight in food daily, according to the FAO. Egypt is Africa’s biggest wheat grower, with expected output of 8.5 million metric tons in the 2012-13 season, according to the International Grains Council.

“The situation remained serious in breeding areas along both sides of the Red Sea where adult groups and small swarms laid eggs,” the FAO wrote. “Although control operations were undertaken, more breeding is expected and small hopper bands and swarms are likely to form.”

Locust numbers in the Sahel, which spans nations from Senegal to South Sudan, declined because of control operations and drying conditions, the FAO said. Small-scale breeding and low temperatures will cause populations to increase slowly in northwest Africa, according to the agency.

Swarms containing tens of millions of the insects can fly as much as 150 kilometers (93 miles) a day, and a female locust can lay 300 eggs in her lifetime, according to the agency.

Desert-locust distribution can extend over 60 countries during plague years, covering about 29 million square kilometers, or about a fifth of the world’s land, according to the FAO.