Tiger moths, known for their striking appearances, often raise questions about their potential to be poisonous. Many species within the tiger moth family (Arctiinae) possess defense mechanisms that make them unpalatable or toxic to predators. This system of self-protection is a significant aspect of their survival.
Chemical Protection Strategies
Tiger moths employ chemical defenses against predators such as birds and bats. Their chemical arsenal is acquired through two main strategies: sequestration from their diet or internal synthesis.
Many tiger moth species obtain toxins by feeding on specific host plants during their larval, or caterpillar, stages. For instance, some caterpillars consume plants containing pyrrolizidine alkaloids (PAs), such as ragwort or senecio. These ingested compounds are then stored within the moth’s body tissues, persisting into their adult form.
Some tiger moths also produce defensive chemicals internally. The presence of these chemicals makes them distasteful or toxic, effectively deterring predators who learn to avoid them after an unpleasant encounter.
The Nature of Their Toxins
The specific toxins found in tiger moths vary by species, but pyrrolizidine alkaloids (PAs) are a common and well-studied group. These compounds, often acquired from their larval diet, render the moths unpalatable and can cause physiological distress to predators. For instance, if a bird consumes a tiger moth containing PAs, it may experience nausea or other adverse effects, learning to avoid such prey in the future.
Beyond PAs, some tiger moths contain neurotoxic choline esters, which interfere with nerve receptors in predators. When threatened, certain species, like the Garden Tiger Moth, can release a yellow, irritating fluid from glands behind their head. While these toxins are primarily effective against predators, human contact with some species’ larval hairs or defensive fluids can cause skin irritation or mild allergic reactions. In rare cases, such as with Asota caricae species, exposure to body fluids and scales has been linked to more severe human reactions, including fever-like symptoms, though direct ingestion is generally required for significant harm.
Visual Warnings and Imitation
Tiger moths display their toxicity through aposematism, or warning coloration. Their vibrant patterns, often featuring bright colors like orange, yellow, red, and black, serve as a clear visual signal to predators.
Many tiger moths also employ acoustic warnings. They can produce ultrasonic clicks that deter nocturnal predators like bats, which rely on echolocation for hunting. These clicks can either signal their distastefulness or even jam the bats’ sonar systems, making it difficult for the bats to locate them.
Some tiger moth species engage in mimicry, where they evolve to resemble other toxic species. Batesian mimicry occurs when a harmless or less toxic species evolves to mimic the warning signals of a highly toxic tiger moth.
Differences Across Tiger Moth Species
The extent of toxicity varies among the thousands of tiger moth species. The level of chemical defense often depends on factors such as their specific diet during the larval stage and their geographical location.
For example, the Cinnabar Moth (Tyria jacobaeae) is well-known for its high toxicity, as its caterpillars feed on ragwort and sequester large amounts of pyrrolizidine alkaloids. Conversely, while the Garden Tiger Moth (Arctia caja) is considered toxic due to compounds like choline esters, direct human interaction primarily results in irritation from their hairs or defensive fluid rather than severe poisoning. The risk to humans from tiger moths is generally low and is typically limited to minor skin irritation upon contact or, rarely, through accidental ingestion.