Wasps move in on ant–plant partnership, disrupting a 10‑million‑year mutualism

An international team of scientists from Queen Mary University of London, the Royal Botanic Gardens, Kew, the Biology Centre of the Czech Academy of Sciences and other institutions has uncovered surprising new behaviour in the tropical forests of Malaysian Borneo. In a study published in PeerJ, the researchers report that predatory wasps are increasingly taking over the hollow stems of the tropical plant Macaranga pearsonii — structures the tree has evolved specifically to house protective ant colonies. 

For millions of years, these “ant‑plants” have relied on a tightly knit partnership with ants. The plants construct specialised hollow chambers and even provide nutritious food bodies, and in return, the ants aggressively defend their host from leaf‑eating insects such as caterpillars. This mutually beneficial system has helped both species thrive for at least 10 million years. 

But now, this ancient alliance is being disrupted. 

Predatory wasps take advantage of plant-made shelters 

By dissecting young Macaranga pearsonii trees across logged forests and oil palm plantations, the researchers discovered that a species of wasp is co‑opting these hollow chambers for its own use — with significant consequences. 

Lead author Mr. Lestina explained: 

“While surveying these ant‑plants, I noticed that many stems had been hollowed out in an unusual way. When we opened them, they were full of flies being eaten alive by wasp larvae. Adult wasps hunt and paralyse the flies, then store them inside the plant’s cavities as food for their young.” 

The study found that plants in oil palm plantations were far more likely to house these wasps than plants in logged forest. Crucially, trees occupied by wasps consistently supported much smaller ant colonies, suggesting the wasps may be displacing the ants entirely, although experiments would be needed to test this. 

Human‑driven habitat change may be helping the wasps spread 

Co‑author Dr Kalsum M. Yusah explains: 

“Human activities are transforming habitats worldwide, and this kind of shift in species interactions is exactly what we expect to see. We don’t yet know whether this wasp is native or introduced, but its spread is clearly linked to disturbed landscapes.” 

Because Macaranga species are among the first to colonise cleared or damaged areas, weakened plants could impair wider forest regeneration. 

“If the plants lose their ant defenders and become less healthy, it could hinder forest recovery following disturbance,” Dr Yusah added. 

Long-term evolutionary impacts could follow 

Senior author Dr Fayle from Queen Mary University of London emphasised the broader evolutionary implications: 

“When mutualistic benefits break down, it can drive long-term evolutionary change. If these structures become less valuable to the plants because wasps exploit them, the plants may stop investing in them. These subtle, long-term consequences of human activity are far less understood than straightforward biodiversity loss.” 

The ant-plant relationship is one of thousands of tightly linked relationships in tropical ecosystems. If human disturbance allows new “invaders” - even native ones – we may see more mutualisms destabilised which could result in weaker natural defences in plants and shifts in which species dominate forests. This study serves as an early sign of how subtle ecological interactions can unravel long before species are driven to extinction.  

 DOI and weblink. 10.7717/peerj.20984.