Do Praying Mantises Eat Poisonous Caterpillars?

Chinese Mantis Consumes Toxic Caterpillars Other Predators Avoid

Although the Monarch butterfly caterpillar (Danaus plexippus) itself is not toxic, it possesses a fascinating defense mechanism called "toxicity by proxy" or "secondary toxicity,” which means that it acquires and stores toxic compounds from the plants it consumes, making it unpalatable and potentially toxic to predators.

However, Chinese mantises (Tenodera sinensis) have a unique ability to consume toxic caterpillars, including those of Monarch butterflies, without experiencing any adverse effects.

Why Are Monarch Caterpillars Toxic?

Monarch caterpillars feed exclusively on milkweed plants containing cardiac glycosides and toxic chemicals. These cardiac glycosides are responsible for the caterpillar's toxicity. When the caterpillar ingests these toxins, it sequesters them in its body, specifically in the cuticle, gut, and tissues.

Why Doesn't the Toxin Kill Mantises?

The toxic larvae's potent defense deters ants and birds, but the Chinese mantis has developed a unique strategy to overcome this obstacle. It skillfully disembowels the larvae, extracting their intestines before consuming the remainder of their bodies.

Once the mantis secures its prey, it begins to chew on it, eventually puncturing a hole through which the guts of the caterpillar spill out. Approximately 40 percent of the caterpillar's body ends up discarded and goes to waste.

Poisonous Tissues Still Consumed

Research findings indicate that the levels of toxic compounds in the caterpillar's guts are identical to those found in the rest of its body. Therefore, it appears that the mantis does not avoid consuming the poisonous tissues of the caterpillar.

Do Mantises Tolerate the Toxins?

One theory that might explain this is that the mantis may be susceptible to certain types of toxins while being tolerant of others. The caterpillar's body contains approximately three times as many variations of these chemicals as its guts, although at lower concentrations.

This observation suggests that the caterpillar may process or break down the toxins obtained from the milkweed before storing them in its other tissues. It is plausible that the mantis can withstand these processed forms but aims to avoid the original, potentially more harmful versions in the guts.

Or Do They Avoid Caterpillar Guts?

An alternative hypothesis suggests that the mantis simply finds the guts unappetizing or not as nutritionally valuable compared to other tissues. The guts typically contain partially digested plant matter and have a lower nitrogen content than other parts of the caterpillar's body.

Therefore, it is possible that the mantis selectively feasts on the more nutrient-rich tissues and discards the nutrient-poor guts. This behavior may inadvertently lead to a reduced intake of poison, coincidentally reducing the overall amount of toxins consumed by the mantis.

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Adult Butterflies Are Toxic Too

The toxicity of Monarch caterpillars carries over to the adult butterfly stage. Even after metamorphosis, adult butterflies retain the toxic compounds obtained during the larval stage. This toxicity serves as a defense mechanism throughout their lifespan.

Predators attempting to consume Monarch caterpillars or butterflies often experience vomiting, reduced feeding, or even death due to the cardiac glycosides in their bodies. The toxins interfere with the predator's heart function and can disrupt its ability to regulate heartbeat and blood pressure.

The toxicity of Monarch caterpillars and butterflies is an example of an adaptive defense mechanism, allowing them to survive in the face of potential predators and thrive in their natural habitats.

How Do Mantises Consume Toxic Prey?

Their ability to consume the toxic caterpillars could be attributed to several factors:

• Chinese mantises possess specialized enzymes in their digestive system that can break down and neutralize the toxic compounds in the caterpillars. These enzymes help the mantises metabolize and detoxify the chemicals effectively, preventing any harm to their bodies.
• Chinese mantises have likely evolved over time to tolerate and even thrive on a diet that includes toxic prey. Their digestive system, including the gut and associated organs, may have adaptations to cope with the toxins and avoid negative effects.
• Their ability to consume toxic caterpillars gives Chinese mantises an advantage in their ecological niche. They can access a potentially abundant and less competitive food supply by exploiting a food source that other predators may avoid.
• While Chinese mantises consume toxic caterpillars, they still prefer non-toxic prey when available. The ability to tolerate toxins does not necessarily imply that they actively seek out toxic prey. They are generalist predators and consume various insects and other small invertebrates based on their nutritional needs and prey availability.

If you're offering them a prey item and they're hungry, they immediately turn and they look at it, and then they almost sort of vibrate, you know, like they're spring-loaded."

— Lisa Gonzalez, Natural History Museum of Los Angeles County

More Facts About Chinese Mantis

The Chinese mantis is native to Asia but has been successfully introduced to various parts of the world, including North America, where it has established populations. It is one of the largest mantis species, growing up to five inches long. These are some more interesting features of this exciting species:

• One of the distinguishing features of the Chinese mantis is its overall green or brown coloration, which helps it blend into its natural surroundings, such as grasses and vegetation. In addition, it possesses a long and slender body with elongated wings, allowing it to be adept at walking and flying.
• Chinese mantises are known for their voracious appetite and impressive hunting abilities. They are ambush predators, patiently waiting in a motionless stance for unsuspecting prey to come within striking range. Then, with lightning-fast reflexes, the mantis captures its prey using its raptorial forelegs, lined with sharp spines. It then quickly grasps and immobilizes the prey, delivering a swift and precise bite to subdue it.
• Another notable characteristic of the Chinese mantis is its reproductive behavior. During mating, the female mantis may display cannibalistic behavior, consuming the male either during or after copulation. This behavior is believed to provide the female with a nutritional advantage for egg production. However, not all mating encounters end in cannibalism, and some males can successfully mate and escape unharmed.
• Chinese mantises are generally found in various habitats, including gardens, fields, and forests. They are considered beneficial insects in agricultural and garden settings as they help control populations of pest insects, such as grasshoppers, crickets, and moths.
• As an introduced species in certain regions, Chinese mantises have raised concerns regarding their potential impact on native ecosystems. In addition, they can be competitively dominant, potentially outcompeting and displacing native mantis species. Therefore, their introduction and spread are often monitored and managed to mitigate adverse ecological effects.

Chinese Mantis Chews Head Off Hornet

Sources

1. Yong, Ed (Jan 25, 2013). National Geographic Magazine. Chinese Mantis Guts Its Toxic Caterpillar Prey
2. Rogers, Nala (June 23, 2020). Inside Science. Lessons About Love and Invasion from America's Foreign Mantises

© 2023 Mike and Dorothy McKenney