When the Federation established a mining colony on the planet in the 2210s, the mother Horta initially tolerated the presence of the miners. But when automated machinery broke onto level 23 in 2267, destroying thousands of Horta eggs in the Vault of Tomorrow, the mother began to fear for her children. She retaliated by destroying parts of the machinery with her powerfully corrosive acid, and when a maintenance engineer came to repair it, she killed him.