In China, orange growers have used ants to keep their crops pest free since 304 CE. The World Health Organization says that pesticides are among the leading causes of death by self-poisoning in low and middle income countries. In Punjab, researchers compared the yields of mango and citrus trees with and without ant nests. And they found the trees with ant nests produced 18% and 20% higher yields than trees without nests in mango and citrus respectively. Palms with ant nests also produced more fruits.