In the America's, the winter hibernation locations of Mexico and California are rapidly shrinking due to deforestation, harsh
weather, development and other habitat disruptions. Because monarchs gather only in a few locations, the overall population is at risk.
The biggest threat is climate change.
Females lay 300-400 eggs (about 40 per day) on the underside of milkweed leaf (swan plant) attached with a special glue like substance. As the larva develops, the egg changes in colour. It is grey when it is about to hatch and the black head is visible. Hatching occurs in 4-8 days. They eat their way out of their eggshell and eat the shell which is full of protein.
The baby caterpillar spends its time eating plants in order to grow. In 2-3 weeks, the caterpillar grows about 2,700 times its birth weight. Its main food source is milkweed (swan plant).
The caterpillar moults five times through it growing stage. As it grows, it becomes too big for its skin (exoskeleton) so it moults or sheds its skin.
After the caterpillar is fully grown, it will find a sheltered place to attach itself in an upside down "J" shape. It will then start the process of metamorphosis, that is, transforming from the caterpillar into the butterfly within the chrysalis, which can take 10-28 days. Within the chrysalis, the caterpillar dissolves into a soup-like fluid, then reforming its cells into the structure of the butterfly.
The monarch butterfly will emerge hanging upside down from the pupa with an enlarged abdomen that is full of fluid. By hanging downwards, gravity will help them pump the fluid from the abdomen into their wings. This allows the wings to expand and dry so the monarch can use them to fly.
Monarch butterflies typically live from 2 to 6 weeks, except for the last generation of the season, which can live up to 8 to 9 months during the winter.
The female have thicker black webbing (veins) within their wings, and darker abdomens that are shaped differently. The males have two black scent glands spots at the centre of the hindwings to attract females.
Garden plants rich in nectar will attract monarch butterflies. The most important part of the breeding program is the monarch butterfly food source, that is, a species of the milk weed plant, or more commonly referred to as the Swan Plant, due to the shape of the seed pod. .
Monarch butterflies in New Zealand do not follow the same migration pattern of their northern relatives. They have adapted their migration behaviour to suit local conditions. When the air temperature drops to 12.8 degrees Celsius (around April or May), monarchs flock together in over-wintering sites. It is assumed there are wintering sites on Waiheke Island. When the temperature warms up, butterflies head inland to reproduce.
Pests of the monarch butterfly include the brown solder bug, praying mantids and wasps. To protect the caterpillar from these pests, we use the netted enclosures to keep them safe from being eaten.