STAGES OF THE INCREDIBLE METAMORPHOSIS
Egg (3 to 5 days)
Once the male and the female mate eggs are laid on the underside of a milkweed plant during the spring and summer months. They are so small that they will fit on top of a needle. Eggs take 3 to 5 days to hatch. When the caterpillars is close to hatching the top of the egg turns black.
Caterpillar (8 to 14 days)
The caterpillar goes through five major distinct stages of growth and after each one, it molts. Each caterpillar, or instar, that molts is larger than the previous as it eats and store energy in the form of fat and nutrients to carry it through the nonfeeding pupal stage.
- The first instar caterpillar that emerges out of the egg is pale green and translucent. It lacks banding coloration or tentacles. The larvae or caterpillar eats its egg case and begins to feed on milkweed. It is during this stage of growth that the caterpillar begins to sequester cardenolides. The circular motion a caterpillar uses while eating milkweed prevents the flow of latex that could entrap it.
- The second instar larva develops a characteristic pattern of white, yellow and black transverse bands. It is no longer translucent but is covered in short setae. Pairs of black tentacles (stinkhorns) begin to grow. One pair grows on the thorax and another pair on the abdomen.
- The third instar larva has more distinct bands and the two pairs of tentacles become longer. Legs on the thorax differentiate into a smaller pair near the head and larger pairs further back. These third stage caterpillars began to eat along the leaf edges.
- The fourth instar has a different banding pattern. It develops white spots on the prolegs near the back of the caterpillar.
- The fifth instar larva has a more complex banding pattern and white dots on the prolegs, with front legs that are small and very close to the head.
At this stage of development, it is relatively large compared to the earlier instars. The caterpillar completes its growth. At this point, it is 25 to 45 mm long and 5 to 8 mm wide. This can be compared to the first instar which was 2 to 6 mm long and 0.5 to 1.5 mm wide. Fifth instar larvae increase 2000 times from first instars. Fifth-stage instar larva chew through the petiole or mid-rev of milkweed leaves and stop the flow of latex. After this, they eat more leaf tissue. Before pupation, larva must consume milkweed to increase their mass prior to pupation. Larva stop feeding and search for a pupation site. The caterpillar attaches itself securly to a horizontal surface, using a silk pad. At this point, it latches on with its hind legs and hangs down. It then molts into an opaque, blue-green chrysalis with small gold dots. At normal summer temperatures, it matures in a few weeks. The cuticle of the chrysalis becomes transparent and the monarch’s characteristic orange and black wings become visible. At the end of metamorphosis, the adult emerges from the chrysalis, expands and dries its wings and flies away. Monarch metamorphosis from egg to adult occurs during the warm summer temperatures in as little as 25 days, extending to as many as seven weeks during cool spring conditions. During the development, both larva and their milkweed hosts are vulnerable to weather extremes, predators, parasites and diseases; commonly fewer than 10% of monarch eggs and caterpillars survive.
Chrysalis (9 to 14 days)
In the pupa or chrysalis stage, the caterpillar spins a silk pad on to a horizontal substrate. It then hangs from the pad by the last pair of prolegs upside down, resembling the letter ‘J’. It sheds its skin, leaving itself encased in an articulated greenexoskeleton. During this pupal stage, the adult butterfly forms inside. The exoskeleton becomes transparent before itecloses (emerges), and its adult colors can finally be seen.
The adult butterfly emerges after about two weeks, and hangs until its wings are dry. Fluids are pumped into wings and they expand and stiffen. The monarch expands and retracts its wings, and once conditions allow it then flies to feed on a variety of nectar plants. Monarchs typically live two to five weeks during the breeding season.
Males that are fit are more likely to mate. Females and males typically mate more than once. Females that mate several times lay more eggs. Mating for the overwintering populations occurs in the spring, prior to dispersion. Mating is less dependent on pheromones than other species in its genus.
Courtship occurs in two phases. During the aerial phase, the male pursues and often forces the female to the ground. During the ground phase, the butterflies copulate and remain attached for about 30 to 60 minutes. Only 30% of mating attempts end in copulation, suggesting that females may be able to avoid mating, though some have more success than others. During copulation, the male transfers the spermatophore to the female. Along with sperm, the spermatophore provides the female with nutrition to aid her in egg-laying. An increase in spermatophore size increases the fecundity of
female monarchs. Males that produce larger spermatophores also fertilize more females’ eggs.