Caterpillar Mimics Venomous Coral Snake

Background

Aposematic Batesian mimicry occurs when one relatively harmless species has a close resemblance to a dangerous or poisonous different species. Over time, as the two species live in close proximity, the individuals of the harmless species that more closely resemble the dangerous species will have higher survival and reproduction rates, leading to a population that appears dangerous. This mimicry is often observed in snakes. For example, many species appear to have the same red, black, and white color patterns of venomous coral snakes. However, mimicry can occur between completely unrelated species as well, such as snakes and caterpillar larvae in the Philippines. This study observed the similarities between the color patterns of the Bracca moth larvae and the coral snake, Hemibungarus calligaster, on Luzon Island.

Study’s Findings

After collecting specimens of each species and measuring and observing the colored bands, it was determined that the patterns of the colored bands observed on the Bracca larvae are more closely similar to another subspecies of coral snakes, the Hemibungarus calligaster cf. mcclungi. This second subspecies is found on the Bicol Peninsula of Luzon Island. This species has a white band that is clearly defined and separates the black bands, a pattern that closely resembles the banding pattern of the larvae. However, the white bands are absent or do not separate the black bands on the first subspecies of coral snake. There are other small differences as well. For example, the larvae have more black bands between red bands than either species of snakes, and its red bands encircle its whole body, while the coral snake only have red bands on their underside.

Since the larvae live in the same mainland area as the first subspecies of snakes, these results suggest that the mimicry is not perfect. Because the larvae more closely resemble the second subspecies, this could suggest that the mimicry system evolved between the larvae and a single species of snakes before the two subspecies differentiated. The caterpillar’s coloring may be similar enough to the coral snakes on the mainland of Luzon Island to reduce predation enough that the differences do not have an impact on survival. In fact, it has been observed that the caterpillars and both subspecies of snakes have similar defensive movements of flashing their colored bands. Future research can determine how quickly avoidance from predators disappears as the geographic distance from the coral a snake is increased.

— Matthew DeRuyter

Siler, C.D. and L.J. Welton. 2010. Geographic variation in Philippine mimicry system: Hypothesized widespread coral snake (Hemibungarus calligaster) mimicry by Lepidopteran larvae (Bracca sp.) on Luzon Island, Philippines. Herpetological Review 41(4): 427–430. pdf