Drop an ant into water and it struggles. Give a colony water, a food reward and a pile of sand, and it builds infrastructure. In 2020, Aiming Zhou at Huazhong Agricultural University and Jian Chen of the USDA published one of the cleanest tests of invertebrate problem-solving on record. The subject was the black imported fire ant, Solenopsis richteri. The apparatus was deliberately crude: a shallow container of 15% sugar water, and loose sand grains scattered nearby. Baseline behaviour was unremarkable. A fire ant’s cuticle is hydrophobic, so workers simply walked out onto the liquid surface and fed. No drowning, no tools required. Then the team changed exactly one variable. Adding TWEEN 80, a non-toxic surfactant, cut the surface tension and turned a walkable film into a lethal one. The behaviour flipped: - Workers stopped entering the container entirely - They began ferrying sand grains to the rim, depositing them inside and outside the wall - The two deposits met to form a conti...