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How caterpillars evade predators

Caterpillars mimic each another to avoid being attacked by predators, a new study has revealed. One caterpillar may look like a stick, while another disguises itself as bird droppings.

india Updated: Dec 17, 2011 15:22 IST

Caterpillars mimic each another to avoid being attacked by predators, a new study has revealed.

In the world of insects, high risk of attack has led to the development of camouflage as a means for survival, especially in the larval stage. One caterpillar may look like a stick, while another disguises itself as bird droppings.

Though crypsis may have its advantages, University of Florida researchers uncovered some of the most extensive evidence of caterpillars using another strategy previously best-known in adult butterflies: mimicry.

Insects use camouflage to protect themselves by looking like inanimate or inedible objects, while mimicry involves one species evolving similar warning colour patterns to another.

The study helps scientists better understand how organisms depend upon one another, an important factor in predicting how disturbance of natural habitats may lead to species extinctions and loss of biodiversity.

“Mimicry in general is one of the best and earliest-studied examples of natural selection, and it can help us learn where evolutionary adaptations come from,” said UF lepidopterist Keith Willmott, lead author of the study and an associate curator at the Florida Museum of Natural History on the UF campus.

The study focused on two groups of Neotropical caterpillars: Danaini of the Caribbean Island of Hispaniola and Ithomiini of the upper Amazon in eastern Ecuador. Sourakov raised and observed danaine caterpillars, including the monarch butterfly and its relatives.

These species apparently form Mullerian mimicry rings, in which toxic species adopt the same warning colour patterns so a predator will more quickly learn which species to avoid.

In Ecuador, Willmott and study co-author Marianne Elias, from the Muséum National d’Histoire Naturelle in Paris, found that 22 of 41 ithomiine caterpillars displayed some kind of warning coloration.

Five exhibited a previously undocumented pattern with a bright yellow body and blue tips, and four were likely Batesian mimics, in which edible species adopt the coloration of an unpalatable model species for protection.

These ‘freeloaders’ only appear to have the defense mechanisms of the model species.

“They act almost like parasites, because the mimics are actually edible and therefore deceive predators without having to invest in costly resources to maintain toxicity,” Willmott said.

“Such a system can only be stable when the mimics are relatively rare, otherwise predators will learn the trick and attack more individuals of both mimics and models, driving models to evolve novel color patterns to escape the predators,” he added.

The study has been recently published in The Annals of the Entomological Society of America.