We were half way to the village of Malual Baai when we came across the two women digging by the side of the road. One turned the thick soil with a small hoe, the other threw it into a basket sieve. The ground teemed with millions of soldier ants.
The older woman, Aguek, explained what they were doing: "The ants, they store away the grass seed under the ground, we know that. So we dig up their nest, and find the food."
Here, at the end of the 20th century, were two women in the heart of Africa fighting with ants for something - anything - to eat. Aguek's daughter sieved out the seed from the ants and the soil and deposited it in a basket.
They had walked an hour from Malual Baai to get here at 6 a.m. and had collected about two cupfuls of seed by the time we arrived. Aguek explained that they would later crush this, remove the chaff, and then boil it to make a sort of soup.
"We have been eating wild foods but some of these are finished," she explained, sipping some discoloured water from a gourd by her side. She is bare from the waist up, and the skin of her empty stomach folds and wrinkles to the skirt-line like the bottom of a curtain.
We met several more groups of seed-gathering women on our 10mile bike journey to the village. And everywhere in this flat savannah where nothing now grows, people said they had been living for months on a diet of wild fruits, leaves and little else.
Finally, I understood what the experts meant when they described the crisis in southern Sudan as a "pre-famine". Certainly, these people have food to eat - if you count weeds, bitter fruit and seeds pillaged from ants as food. But for how long can they continue to survive on these meagre foods?
In another hut along the way, a woman shows us her foodstore for the week. There is a basket of tamarind seeds for roasting. She will separate the kernel and the husk and cook both separately to feed the seven people who sleep by their four goats in this beehive hut.
Another gourd holds a pile of leaves from the lalok tree, which will make a good soup, she says. When we arrive, she is cracking open some goat bones to get at the marrow, which will also make a broth. The woman says the last time she saw a bowl of sorghum was in December.
Annalies Borrel, a nutritionist with Concern, said: "It's phenomenal that they have survived on this. The calories in their diet just don't add up."
Southern Sudan's crisis is the sum of thousands of such small struggles, endured across a vast swathe of arid, flat savannah the size of France and Germany together.
The picture emerging is one of simple communities which are used to coping with war and climatic extremes like drought, but which was now slipping towards the edge of some frightful abyss.
Along the road, at the market in Madol, you can buy sugar and salt and ground nuts, but there are no vegetables and no grain. People have started to slaughter their goats, a traditional sign that there is no other food available.
Food drops by the World Food Programme has helped in some areas, and Irish aid agencies like Concern, Goal, Trocaire and World Vision Ireland have made a contribution. But away from the airstrips, thousands of people are on the brink of starvation.
On reaching Malaal Baai, the Concern assessment team and myself are greeted with enthusiasm by the chief, a Dinka who stands two metres tall and wears dark glasses and a hat like a tea cosy. The village has a dirt airstrip but since it is not on the map used by pilots, no kawayah (whites) have landed there since the villagers cleared it over two years ago.
"My people have lost their cows and they have lost their grain in the looting. Now they are losing their health. Twice we were told help was coming but it has not arrived," says the chief, Piota Eyi, over a round of hot, sweet tea.
Because of the drought there is no pasture, and just that night, the chief said, four of the village's cattle had died. Because the community had no crops with which to pay the teacher, the school had closed. There were no medicines in the village and the clinic was shut.
Our plane hops from airstrip to airstrip but everywhere the tales of looting and killing are the same. Armed by the Khartoum government to create a buffer zone between the north and the rebel south, Arab militias have wreaked havoc in hundreds of villages.
Far to the west, the town of Nyamlel has been sacked by the invaders. Some of their victims lie half-buried near the piles of horse dung that mark the spot where the Arabs made their camp.
They stayed a week, rounding up the cattle and goats, raping the young women and shooting older ones in the feet, according to a local relief official. Thousands of those who fled have returned, and are sleeping in the open.
Many had gathered yesterday for a food distribution by WFP but the official said this would reach less than 5 per cent of the villages. Most of all, they needed tools to start tilling in time for the rains, he said.
In Mariel Bai, a local man, Gau Gaurwirr, told me his wife and five children had been abducted by the horsebacked invaders. Their fate is likely to include rape and slavery. Gau has just returned to his burnt-out compound, after hiding out in the bush for two weeks.
Meanwhile, in other parts of southern Sudan, the business of war continues as normal. The rebel Sudan People's Liberation Army claimed it killed more than 300 government troops when the latter attacked SPLA positions near the Nile.