Invertebrates ...

Monarch Butterfly; Milkweed Butterfly
Danaus plexippus
Family: Nymphalidae
Order: Lepidoptera
North American monarch butterflies arrived in Hawaii between 1841 and 1852 following the establishment of the milkweed (Asclepias curassavica), their primary host plant. The crown flower (Calotropis gigantea), and the balloon plant (Gomphocarpus physocarpus) also serve as hosts. This orange butterfly is recorded on all the main Hawaiian Islands, with a white form on O`ahu and in Kona, Hawaii, and a rare brown form on Kaua`i.

Monarch butterflies have a very short life of six to eight weeks and go through a complete change called metamorphosis in what looks like four distinct stages - egg, larva, pupa, adult.








Egg - the size of a pinhead with longitudinal ridges is usually laid on the underside of a new leaf near the top of a milkweed plant (like the crown flower, balloon plant, or butterfly weed).






Larva – a tiny caterpillar emerges in four days, the first thing they eat is the egg shell. Caterpillars have six jointed true legs and 10 prolegs to help it move from leaf to leaf, and two sets of tentacles on the first and last body segments. There are six pairs of simple eyes called ocelli on the lower part of the head capsule which will not grow any bigger. Despite having all those tiny eyes their vision is poor and the tentacles help guide them. They breathe through a series of holes called spiracles in the sides of their thorax and abdomen.

For the next 10-20 days (usually two weeks) the caterpillar is an eating machine whose body grows from 1/16” to 2” and increases in weight 2,700 times. The larva will stop eating four times to molt/shed its too small skin or exoskeleton. After shedding the caterpillar usually eats the skin then eagerly eats the nearest leaf, moving head and jaws in a top to bottom fashion. When the fifth skin is tight again eating stops and a search for a safe place begins.

Once a place is chosen the caterpillar will spin a mat of silk, from a spinneret located on the bottom of the head, on a twig or other high spot. It then uses its last set of prolegs called claspers to firmly grab the silk mat where it will hang upside down in a “J” shape for a day. Then it straightens out and begins to twist and turn until the skin behind the head splits and the fifth and last stripped caterpillar skin is discarded.



Pupa - Just before the skin is dropped, a black appendage at the end of the abdomen with barbed hooks on the tip is twisted into the silk pad. This post is called a cremaster and must get firmly hooked into the silk or the pupa will fall and die. The soft green casing changes shape and the yellow stripes move upwards to form a line of golden dots. This pupal casing or shell hardens and is called a chrysalis.

Since the only silk made was used to attach the chrysalis, not to make a silken covering, it is incorrect to call it a cocoon. Most moth caterpillars, but not all, will spin a silk cocoon to protect them while they pupate. If you find a cocoon - a butterfly will never come out of it - only a moth.

The pupa stage lasts 10 -15 days. During the last few days before emerging the butterfly begins to get its color and the orange and black scales on the wings become visible inside the transparent chrysalis.



Adult - When ready the butterfly pushes itself out head first and holds on to the pupa casing, swinging the abdomen down and letting the crumpled wet wings hang down. Then they pump fluid from their abdomen into their wings along the black veins, which give strength and structure to the wings. The wings dry and harden in about three hours. While their wings are drying, they will get rid of a reddish liquid that is waste product from their transformation.

After emerging the new adult butterfly can be seen stretching and rolling and unrolling its long proboscis, which is like a double straw, for sucking nectar from flowers. After the wings have been stretched and dried it is ready to take to the air for the first time. But if it is cold, windy, or rainy the butterfly will wait until the following day to start its new life in the air.

Male monarchs are easy to identify by the spots on the hind-wings. These are really scent packets used to attract the females. Male veins also look much thinner than the broader and fuzzier veins of the female. The coloration on the underside of the wings is similar to the top with the hind wing being a more golden orange, and the spots of creamy-white are more pronounced.

The first activity will probably be to seek out flowers where its feet (tarsus), which are used to grip vegetation, will also be able to taste the sweet nectar. The adult butterfly may look like it only has four legs but the front two are small, clawless, incapable of walking, and held close to their black fuzzy body






Butterfly body sections are the same as all insects - head with compound eyes and two knobbed antennae, the thorax with six legs and two sets of wings covered in tiny scales, and an abdomen. The butterfly is now 3 ½ to 4” and finished growing. Nectar is used for energy during the remaining two to five weeks of life. In 7-10 days the butterflies will be ready to mate. That is when the black pockets of the males are used to release pheromones to attract the females. He sprinkles her with his perfume and grasps her with his feet and they flutter to the ground. For the next ten minutes or more it looks like a wrestling match as they get into position. The female folds her wings and the male flies with her dangling upside down to the tops of trees where they will remain together for hours. The male may mate three times before dying.

The female will lay 100’s of eggs (400-900) usually on the underside of young toxic milkweed leaves. She is ensuring the next generation of a food source which will not only nourish them but make them taste terrible to predators. The new caterpillar's bold yellow, black and white stripes will announce to all “don’t eat me!”

After laying her eggs and delighting all who see her gracefully fluttering in the air, she returns to the earth as her short life ends.




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