1. The study examines the larvae of the beetle Hexodon unicolor unicolor in rice crops in Madagascar and finds it can act as a "soil engineer". 2. Experiments show the abundance of H. unicolor larvae depends on the season and type of crop residues present, with lower densities in crops with Raphanus sativus and Crotalaria grahamiana residues. 3. The mortality of H. unicolor larvae is higher in systems without residues and lower in those with legume residues like soybeans and Stylosanthes guianensis. Rice growth is better with those residues and cow manure, irrespective of larvae presence.