Green anacondas in both habitats have been found to feed on large prey, usually ranging from 14% to 50% of its own mass. Prey availability varies more in grasslands than in river basins. As they develop, their diet becomes increasingly complex. Juvenile anacondas feed on prey such as small birds and juvenile caiman that are typically 40-70 grams in size.
Their diet includes various aquatic and terrestrial vertebrates such as fish, reptiles, amphibians, birds, and mammals. Green anacondas are opportunistic apex predators, feeding on any prey that they can kill and swallow. Dracunculus brasiliensis (Family Dracunculidae, Phylum Nematoda).Tabanus occidentalis (Order Diptera, Class Insecta).Stenotabanus cretatus (Order Diptera, Class Insecta).Stenotabanus bequaerti (Order Diptera, Class Insecta).Phaeotabanus nigriflavus (Order Diptera, Class Insecta).Amblyomma fulvum (Family Ixodidae, Class Arachnida).(Phylum Apicomplexa, Kingdom Chromalveolata) Providencia rettgeri (Class Gammaproteobacteria, Phylum Proteobacteria).Aeromonas hydrophila (Class Gammaproteobacteria, Phylum Proteobacteria).
Stenotrophomonas maltophilia (Class Gammaproteobacteria, Phylum Proteobacteria).
Elizabethkingia meningoseptica (Class Flavobacteria, Phylum Bacteriodetes).For the most part, wild anacondas seem to withstand parasitic loads well and are seemingly healthy. Opportunistic parasites are most likely due to suboptimal husbandry and captivity. Captive snakes are also predisposed to diseases. Health assessments of green anacondas in captivity have found that they can harbor a number of internal parasites. Green anacondas act as predators to a wide array of vertebrate species, with young snakes also serving as prey to a number of large predators.