Carnivorous Nepenthes plants derive essential nutrients from arthropods captured in their pitcher-shaped leaves. The pitchers secrete a digestive fluid and house specific microbiota and 'macrobiota', mostly mosquito larvae, that aid in digestion, breaking the prey down into an easily assimilated form. We tested and measured the occurrence of such facilitation processes among Bornean Nepenthes. In a field experiment, prey items were introduced into the fluid of newly open pitchers of four Nepenthes species and their state was compared one month later between control pitchers and pitchers initially closed by insect screening mesh. The same experiment was performed in water-filled glasses. Metazoan diversity, tank dimensions and fluid pH were then measured in the 150 tanks. Prey in macrobiota-deprived pitchers experienced lower degradation than in control pitchers in all Nepenthes species but not in water-filled glasses. Macrobiota exclusion impacted less species characterized by narrower pitchers and more acidic fluids. Rate of prey degradation increased significantly with abundance and diversity of inquilines. Therefore, Nepenthes pitcher plants are largely dependent on their 'macrobiota' to decompose prey. Digestive mutualisms are supposed to be crucial in species whose pitchers have large aperture and less acidic fluids, housing a more diverse infauna and secreting presumably fewer digestive enzymes.