Ethiopian farmer Ahmed Ibrahim batted empty water bottles at a swarm of desert locusts the size of his palms that were devouring his field of khat -the mildly narcotic leaf that is his family’s main source of income.

“We have nothing else to sell at the market. How will I feed my eight children?” he asked helplessly, shouting over the sound of the insects as his children chased them with a yellow headscarf and a stick.

The locusts devoured Ibrahim’s small grazing plot as hisdonkeys brayed anxiously and goats scrambled to eat the remaining foliage. Scenes like this are happening across the Horn of Africa,where swarms of desert locusts have damaged tens of thousands of hectares so far, the Food and Agriculture Organization (FAO)said.

“These infestations represent a major threat to food security in Kenya and across the entire Horn of Africa, which is already reeling from floods and droughts,” said Bukar Tijani,FAO’s Assistant Director General, calling the swarms “vast and unprecedented”.

Breeding is continuing on both sides of the Red Sea, in Sudan and Eritrea and in Saudi Arabia and Yemen, the FAO said. The swarms spread from Ethiopia and Somalia into eastern and northern Kenya last week, threatening food production and the economy, Kenya’s then-agriculture minister said, before being fired in a cabinet reshuffle on Tuesday.

Kenya began aerial spraying in the north on Jan. 4 to head off the invasion. Kenyan media showed police shooting bullets and teargas a tan oncoming swarm as residents banged on buckets and hooted car horns to try to frighten the insects.

A farmers’ association in Kenya’s northern Laikipia area said it was planning aerial spraying of pesticides to combat the worst locust plague since 1954. The FAO estimated one swarm in Kenya to be 40 km wide by 60 km long (25 by 40 miles).

“These things are in their millions and will eat all the vegetation here. Our animals will not have anything to feed on,”said Peter Learpanai, a herdsman in the northern Samburu region who was flapping his jacket at a cloud of the insects that had descended on his grazing land. “The government needs to get serious about fighting them.”