The Green Iguana (Iguana iguana) is a large reptile known primarily for its plant-based diet throughout its native range in Central and South America. These lizards are classified as herbivores, but the question of whether they eat other lizards requires a closer look at their dietary flexibility. Scientific observation confirms that while plant matter forms the bulk of their nutrition, Green Iguanas are opportunistic omnivores. They will occasionally consume small animal matter, including insects, bird eggs, and small vertebrates such as other lizards. This adaptable feeding behavior is a significant factor in their survival, especially in environments where they have been introduced.
The Primary Herbivorous Diet
The Green Iguana’s digestive system is highly specialized for processing tough, fibrous plant material, which confirms its baseline as a herbivore. Their diet in the wild consists largely of the leaves, flowers, and fruits of over 100 different plant species. They typically select young, nutrient-rich leaves and shoots, often foraging high in the canopy of tropical forests.
The ability to extract nutrition from foliage is due to a process called hindgut fermentation. This digestion occurs primarily in the lizard’s sacculated colon, a specialized structure where symbiotic microflora—bacteria and protozoa—break down cellulose. This system is optimized for a high-fiber, low-protein intake. Adult iguanas fed a diet high in animal protein can develop serious health issues, such as kidney failure, due to the strain on their body’s natural processing limits.
Consumption of Other Lizards
Despite their specialized herbivorous gut, Green Iguanas will consume other lizards, though this behavior is opportunistic rather than a primary hunting strategy. This consumption is typically observed when the iguana encounters a small, slow, or already injured vertebrate. The act of eating small vertebrates, including lizards like anoles or geckos, is driven by a temporary need for specific nutrients, particularly protein or calcium, that may be lacking in their current plant forage.
Adult iguanas have been documented consuming small prey such as insects, tree snails, and bird eggs, and they will readily scavenge carrion. The consumption of a small lizard often occurs simply because the prey is in the wrong place at the wrong time, such as a small anole perched on a leaf an iguana is about to ingest. This behavior is considered a form of nutritional supplementation, allowing the iguana to quickly access a dense source of protein or fat. The size difference between a large iguana and a small anole makes the latter a viable, if accidental, meal when the opportunity presents itself.
Age, Environment, and Opportunistic Feeding
The frequency of consuming animal matter is significantly influenced by the iguana’s age and its surrounding environment. Juvenile iguanas exhibit a much higher rate of omnivory than adults. Hatchlings and young iguanas require a high-protein diet to fuel their rapid growth during their first two to three years of life.
Young iguanas lack the fully developed gut microflora necessary to efficiently break down large quantities of cellulose, so they rely more heavily on easily digestible protein sources like insects, eggs, and small prey. Environmental factors also push adult iguanas toward omnivory, especially in disturbed or non-native habitats where optimal plant forage may be scarce. Resource scarcity, such as during a drought or in an area of high population density, can push adults to consume anything readily available to maintain energy.
This flexible feeding strategy is not uniform across all iguana species. For example, the Black Spiny-tailed Iguana (Ctenosaura similis) is known to be far more carnivorous than the Green Iguana, actively hunting small animals as a regular part of its diet. The opportunistic omnivory of the Green Iguana represents a behavioral adaptation to meet nutritional demands under variable conditions.
Ecological Consequences of Omnivory
The opportunistic consumption of animal matter by Green Iguanas takes on a broader significance in regions where they are an invasive species, such as Florida and Puerto Rico. In these non-native environments, the iguanas’ flexible diet can directly impact local biodiversity. The consumption of native bird eggs and nestlings is a specific concern, as it directly reduces the reproductive success of local avian populations.
The general predation on small native lizards, like the Brown or Green Anole, also introduces a new competitive pressure into the ecosystem. Invasive iguanas, with their large size and high population numbers in some areas, can significantly impact the survival rates of smaller, native reptile species. This consumption, combined with the iguanas’ herbivorous damage to native plants, contributes to a shift in the local food web, potentially threatening the stability of vulnerable native reptile populations.