Conclusion. Communal living arrangements, which can occur out of both necessity and security, are examined. Icelandic puffins, for example, form nesting colonies of more than a million; and share the space with other birds, lessening the odds that individuals will be attacked. Social spiders in Ecuador, on the other hand, band together to subdue large prey. Also: leaf-cutter ants in Costa Rica, which build complex, acre-wide cities and societies.