The monarch butterfly is primarily an American butterfly, found from Canada to South America. It has also spread to Europe and Australia. The adult monarch has a wingspan of 3 3/4 to 4 inches. It's wings have an orange and black pattern. Female monarchs have darker veins on their wings, and the males have a spot on each hindwing from which pheromones are released. The viceroy butterfly is a similar size, color, and pattern, but has an extra black stripe across the hindwing. The monarch and the viceroy butterflies are an example of mimicry in nature.
Like most insects the adult Monarch butterfly has 3 main parts to it's body: The head, thorax, and abdomen. There are four main parts to the adult head: eyes, antennae, palpi, and proboscis. Their compound eyes are made of many ommatidia, each one senses light and images. The two antennae and the two palpi sense molecules in the air and give butterflies a sense of smell. The antennae and palpi are covered with scales. The proboscis is the butterfly's tongue, which it uses to suck nectar and water. The butterfly curls up its proboscis when it's not using it. The thorax is made up of three parts. Each part has a pair of legs attached to it. The second and third segments also each have a pair of wings attached. The legs are made up of six segments. They end in tarsi that grips vegetation and flowers when the butterfly lands. There are organs on the back of the tarsus that are able to taste sweet liquids. Monarch butterflies look like they have four legs because the two front legs are very small and curl up next to the thorax (this is also true with other nymphalid butterflies). All butterflies and moths have two forewings and two hindwings. Tiny structures attach the wings to the thorax; muscles attached to these move the wings. Another way the butterfly can move its wings is by changing the shape of its thorax. Wing veins contain trachea, nerves, and space for hemolymph to flow through. The veins provide structure, strength and support to the wings. The abdomen has eleven segments and the last two or three are joined together.
The mating period is in the spring for the winter butterflies. This happens just before migration from the overwintering sites. The courtship has two stages, the aerial and the ground phase. The aerial phase happens first, when the male pursues, nudges and brings down the female. During the ground phase the male transfers a spermatophore to the female. Monarchs will mate up to seven times in their summer territory. The winter butterflies go as far north as they need to, to find the early milkweed growth. For the eastern butterflies that is usually southern Texas. A Monarch has a life cycle that includes a complete metamorphosis. It goes through four different stages:
- The females lay their eggs during the spring and summer.
- Caterpillars (larva) are hatched from eggs. The caterpillars first eat their egg cases and then feed on milkweed, withdrawing cardenolides. During this stage, the Monarchs store fat and nutrients that they will need in the pupa stage.
- The caterpillar spins a silk pad on a leaf or twig, and hangs from the pad by its last pair of prolegs. This is the pupa or chrysalis stage. It hangs upside down in the shape of a "J", and then molts, leaving itself enclosed in an exoskeleton. Hormonal changes then occur and the pupa develops into a butterfly. A day before it emerges, the chrysalis gets darker and transparent. Its wings can be seen through the exoskeleton.
- After about two weeks the butterfly emerges and hangs from the chrysalis for a few hours, until its wings are dry. This often happens in the morning. While this is happening fluids go into the wrinkled wings until they expand and become stiff. The abdomen also reduces to a normal size and then the butterfly flies away (usually in the afternoon).
Monarchs are poisonous and bad-tasting because of cardenolide aglycones in their bodies. This poison comes from the milkweed plant that they feed on as caterpillars. Its bright colors advertise its poisonous nature. Animals that eat a Monarch get very sick and vomit, but usually do not die. Threats to Monarchs are the destruction of their habitats and a parasite called ophryocystis elektroscirrha (a protozoan). Another possible threat to Monarchs is the pollen of genetically modified Bt corn. This was indicated by a study done in May 1999. Another study was done after that, that said that the risk to Monarch butterflies was negligible.
The Monarch butterfly is a long-distance migrator. They begin massive southward migrations in August until the first frost. The northward migration begins in the spring. However individual butterflies don't complete the migration both ways. Their great-grandchildren end up back at the starting point. In North America there are two large population groups that follow different migration paths. Most Monarchs east of the Rocky Mountains overwinter in the Sierra Madres in central Mexico where they live in fir forests at high altitudes. Far western groups of monarchs winter along the coast of southern California, where they live in groves of pine, cypress, and eucalyptus trees. In the spring they head north and breed along the way. The original butterfly dies along the way, but the offspring it leaves behind continues north, where the cycle will start again in the fall. There are some populations of monarchs in California, Florida and Texas that don't migrate.
Monarch emerging from a chrysalis
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- Monarch Watch BiologyBy Monarch Watch. University of Kansas.
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- The magnificent migrating monarch: An electronic design expert ponders the stunning navigational exploits of the monarch butterfly by Jules Poirier. Creation 20(1):28–31, December 1997.