Uganda has started to spray swarms of desert locusts that invaded over the weekend, posing a major threat to livestock and key crops such as coffee, a government officials has confirmed.

The plague of locusts has already caused extensive damage to pastures and crops and threatened food security in several countries in the east and Horn of Africa, including Somalia, Ethiopia and Kenya.

A single swarm of the insects can measure 40 kilometres wide by 60 kilometres long (25 by 40 miles), according to the U.N. Food and Agriculture Organization (FAO).

“We are using motorised sprayers, a drone and manual sprayers,” Stephen Byantwale, commissioner for crop protection at the ministry of agriculture said.

“They (locusts) are spreading like wildfire, so they are a real, major threat.”

The FAO warned in a report on Monday that locusts were continuing to breed in the Horn of Africa, which would lead to more insects in Ethiopia, Somalia and Kenya, with new swarms forming in March and April.

“There is an unprecedented threat to food security and livelihoods in the region,” the U.N. agency said.

The swarms entered Uganda in the northeastern region of Karamoja on Sunday. Byantwale said if their movement was unchallenged, they were expected to move further south, threatening fields of crops that include coffee, rice, corn and others.

Coffee is one of Uganda’s major exports and a key source of foreign exchange. The country is Africa’s biggest exporter of the beans and tourism is also a key hard currency earner.

Byantwale said the foliage-devouring swarms were also a major threat to Kidepo National Park, found in northeast Uganda and one of the biggest in the country where visitors can see giraffes, zebras and buffalos.