Myrmecodia - Ant Bulb
These small shrubs from Papua-Neuguinea are distantly related with the Coffee Shrub and live as epiphytes or on jungle clearings, where the tropical soil is poor. Already in the seedling stage, the stalk swells and forms an extensive system of chambers that can reach more than 5 l in volume. These chambers are soon settled by ants of the species Iridomyrmex cordatus, that later also distribute the amber fruits that resemble breast warts. The sticky seeds are often integrated into the walls lining the ant highways, such that close to an Ant Bulb soon its progeny will sprout in a neatly aligned row. The chambers provide ideal conditions for the ants that find here protection and shelter.
The benefit of this obviously controlled symbiotic relationship for the plant host had remained enigmatic for a long time. First, the ants were thought to protect their host from herbivor attack, similar to the Mexican Ant Akacia. However, Iridomyrmex cordatus seems to be a very peaceful fellow and does not even react, if somebody charges upon its host plant. ihrer Schutzpflanze zu schaffen macht. Moreover, the Ant Bulb accumulates bitter compounds that are sufficient as protection. The real cause was uncovered only recently: The ants use some of the chambers as toilet and storage for killed prey, whereas other chambers are used to raise their offspring. The nurseries are lined by smooth, water-repellent walls, whereas the walls of the ant toilets are full of warts. These warts harbour glands that allow the plant to take up organic nitrogen from the ant feces and corpses of prey. By this way, the plant can survive even on sites poor in nutrients (uptake of nitrogen from the soil does not work for a epiphytic plant).
By which chemical signals this exotic plant manipulates its ant inmate, is still a complete mystery.