Processionary Caterpillar

Processionary caterpillars demonstrate stigmergy in its purest form. Caterpillars lay silk trails as they move, and followers track the silk with their heads touching the tail of the caterpillar ahead. The result is spectacular single-file processions stretching meters long—dozens of caterpillars following a shared path without any leader knowing the destination. The trail is the guidance system; following behavior is hardwired; complex collective movement emerges from simple rules.

Famous experiments demonstrated the system's limitations. Researcher Jean-Henri Fabre placed processionary caterpillars on a circular pot rim. With no endpoint, caterpillars followed each other in circles for days, each tracking the silk of those ahead, none breaking the loop. The demonstration revealed that stigmergic following lacks error correction—if the trail leads nowhere, followers follow nowhere indefinitely.

Processionary caterpillars also pose human health risks. Their urticating hairs cause severe allergic reactions; climate change is expanding their range northward into previously unaffected European regions. The caterpillars are simultaneously fascinating biological systems and emerging public health concerns. The business parallel illuminates the danger of pure trail-following. Organizations where employees follow precedent without questioning direction risk circular loops—processes that continue because they've always continued, without anyone verifying they lead anywhere useful. Stigmergic coordination enables efficient execution but provides no course correction when the trail itself is wrong.