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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Blue lightning in the rainforest – Blue Morpho, Morpho menelaus


Bold scary eyespots adorn the lower surface of the Morpho’s wings.


With the arrival of a new year and much of the nation firmly embraced by winter’s chill, it’s time to travel south in search of sublime temperatures and tropical insects. The first stop on our sojourn is the rainforest of Costa Rica to visit one of the most beautiful members of the butterfly clan, the blue Morpho. While exploring a small stream transecting the forest I was delighted to see brilliant flashes of blue as a Morpho butterfly loped through a light gap in dense forest canopy.



A beautiful Morpho basks in the sun on a rocky outcropping.

The iridescent burst of blue color, the signature of the blue Morpho, is produced by the physical structure of tiny scales covering its wings. A multitude of thin layers of insect cuticle that  comprise each scale reflect only certain wavelengths of light to produce the shimmering display of blue as the butterfly dances through the forest. This form of physical coloration contrasts with other forms of color we commonly see in insects. In many species of insects, color is produced by storing pigments in the cuticle, or outer covering (exoskeleton), and is employed by insects such as the milkweed bugs we met in previous episodes.

Brightly colored Morpho caterpillars bear tufts of long hairs.

Despite their startling display of color, the blue Morpho has evolved a clever strategy for dealing with would be predators. Intricate patterns of scales on the underside of their hind wings create an illusion of large staring vertebrate eyes, complete with pupils and irises. It is thought that these intricate eyespots are used by the butterfly to startle or otherwise confuse hungry predators such as birds or lizards. Studies have shown that the more closely the pattern resembles an eye, the more likely a predator is to be deterred by the ruse. Another theory suggests that the false eyespot may draw the attack of a predator away from a vital body part such as head or abdomen to a less vital area such as the end of a wing. Only the butterfly and its predators know for certain.

Within chrysalises, Morpho caterpillars transform into beautiful adults.

Fermenting fruit is one of the favorite foods of adult Morpho butterflies, but adults can also be found dining on sap fluxes on tree trunks, minerals at mud puddles, and nutrients from dung. When it comes to eating, morphology butterflies are among the most curious in the insect world. Adult butterflies possess a long proboscis that uncurls to lap up liquid nutrients. Larvae of butterflies are called caterpillars and their mouthparts consist of chewing jaws that remove tissue from the leaves and other foods. More than 20 species of Morpho butterflies are found in the New World tropics and their larvae eat a wide variety of host plants ranging from blades of grass to leaves of legumes. 



A busy proboscis laps nutrients from rotting fruit, one of the preferred foods for many butterflies, including Morphos.


The interesting reference “Amazon Insects” by James Castner was used to prepare this episode.

To learn more about Morpho butterflies, please visit the following web site: