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Anatomy of a Butterfly: Marzo 1, 2022

The monarch butterfly is called mariposas monarchas in Spanish However, the Latin genus and species name for the monarch butterfly is Danaus plexippus. It has 3 pairs of legs but the front two legs are shorter like a T. Rex.

The monarch has sexual dimorphism which means there is male and female. The male has spots on the hind wings called stigmata. The female has wider stripes and no spots. The butterflies remain immature during their stay in Mexico and only become ready to mate when it is time to migrate north. Mating will take place when the temperature rises in Mexico. This triggers the excretion of a hormone and the development of sexual organs of spermatophore or “packages” in the males and eggs in the female. When the butterflies begin moving down the mountain and reach the edge of the forest, they start their migration north. Sometimes they mate before they leave.

The male loses 10% of his body weight and dies soon after mating. Mating can last up to 16 hours. Sometimes two males will get together but shortly realize that the mating won’t work and go their own way. The female may mate several times but only the last one will take. 

There are three major bird predators of the monarch while in the forest and you can tell which one killed the monarch by the monarch. Look at the beaks of the birds.

  1. The black-backed oriole will poke a hole through the abdomen.
  2. The black-headed grosbeak will take a big chunk out of the thorax.
  3. The black-eared mouse will eat the whole part and just leave the wings. These are easy to spot on the ground.

Only one egg is deposited on a leaf. This is for survival and makes it harder for a predator to eat them all. Nothing is wasted in nature. Once the caterpillar emerges, its first meal is the egg casing. 

Next the caterpillar will start to eat milkweed. Milkweed is toxic to all mammals because it contains cardiac glycosides. The greatest amount of toxins are found in the wing.

The milkweed also secretes a latex substance. If the caterpillar did not eat the milkweed properly by cutting off the main vein in the leaf, the latex would glue their mouths shut.

The caterpillar will molt five times. Each stage is called an instar and they continue to eat milkweed. The resulting caterpillar is called an instar. From egg to final caterpillar, the resulting caterpillar is 2,700 times larger than the egg.

Once they reach the fifth instar they will travel about 20-30 yards away in search of a solid branch. Once they have picked their location, they secure their location by making a cremaster made up of a web-like material. They will start to make a chrysalis. Chrysalis means “gold” in Greek.

Once the butterfly emerges from its chrysalis, it will take one hour to pump lymph throughout the veins in its wings and in order for the wings to dry. Next, they will search for nectar plants as they will be hungry. They need to mate within 5 days. The male will die and the female will continue north.  This process will repeat  4 to5 times on their journey north.


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