Re: Monarch Butterflies

> Can you please tell me what the gold dots on a Monarch butterflies 
> (Danaus plexippus) chrysalis are for or are they just decorative?
>Thanks
>Richard

I have to admit that I have taken an easy route to answer your question and posted it again to the lepidoptera newsgroup.

To this I got the hint from someone (EMAIL: monarch@falcon.cc.ukans.edu) to view an excellent WWW site about monarchs. Many thanks to him or her!

The following answer is comprised from direct quotations taken from the information available there.

Q. Why do monarch butterflies all have the same design on their wings?

A. The design or pattern on the monarch's wings is genetically programed. This means that the pattern is determined by genetic rather than environmental factors. The color of our eyes and hair is genetically determined but our height and weight are partly determined by environmental factors such as the amount and quality of food we eat. The pattern on the wings of monarchs is not influenced by the temperatures during larval and pupal development, nor the food plants upon which the larvae feed, however, the size of the adult butterflies is related to the quantity and quality of the leaves the larvae have fed on.

Q. But why do monarchs have this particular design?

A. Colors and patterns of insects are thought to be the result of interactions of each species with their environment. Charles Darwin noted that "evolution is written on the wings of butterflies". By this statement he suggests that the colors and patterns on butterfly wings are the result of long term evolution. Is this true? Well, we don't have a complete understanding of how evolution works in these cases but there are numerous studies of butterflies which demonstrate many functions for color and pattern. For example, in some species color and pattern are used by individuals to recognize members of the same species for mating. Bright and/or contrasting colors, such as the black and orange of the monarchs wings, warn predators that the insects are distasteful (monarchs are distasteful to many predators due to the chemicals, cardenoloids, they acquire from feeding on milkweeds) and, in some cases, dangerous (certain caterpillars with urticating hairs). These contrasting or warning colors are also the basis for mimicry in butterflies and other insects. Butterflies which are distasteful to predators usually have warning colors and patterns on the wings and these species serve as models for mimicry by other insects which are not distasteful to predators. Mimicry seems to work because the predators learn to avoid the color/pattern of the models and this avoidance gives protection to the mimics. In addition to communication within and between species, colors and black (melanic) pigment can also serve to maximize and minimize heat gain due to adsorption of infrared energy from sunlight. Insects tend to be more melanic and "hairier" in mountainous areas and far northern latitudes, where temperatures are low. Black pigments, particularly at the base of the wings, have been shown to enhance convective heat gain from the sun. Tropical species which frequent open, sunny habitats tend to be light in color while those which reside within the forest are usually darker. Within forests, darker colors can help conceal the insects from predators but some species also appear to use these colors to adsorb heat since they are often seen to 'sun' themselves in patches of sunlight when temperatures are low.

Warning coloration refers to the conspicuous bright colors on organisms that contain poisonous, distasteful, or noxious chemicals. Warning colors include bold patterns of yellow, black, orange, and white. Biologists believe these bright colors advertise the organism's distastefulness so that potential predators stay away.

Examples of warning coloration include poison dart frogs from the tropical rainforest and monarch butterflies. Warning coloration may work particularly well in butterflies because the hard body and large wings allow a predator to bite the adult, taste the poison, and release the butterfly without killing it. It is common to see butterflies with beak-sized sections gone from their wings; if the wings contain bitter chemicals, such as the poisonous cardenolides in monarchs, one bad-tasting bite may discourage further attack without killing the adult.

The best-studied defense of monarchs is aposematic coloration. Monarch adults and larvae have bold orange, yellow, white, and black patterns, coloration which many ecologists believe warns potential predators that they contain poisonous chemicals.

If you have more questions about monarchs or butterflies in general try to contact the lepidoptera newsgroup or a listserv discussion group called DPLEX-L that will facilitate discussions among taggers and other interested parties on monarchs or one of the other adresses listed here.

God bless you

Jurgen