Transcript:

Today on Animal Fact Files we’re discussing monarch butterflies. These insects are also known as the milkweed butterfly which is a good common name because their larvae exclusively eat milkweed. Monarch butterflies are found throughout the Americas and have been introduced to Australia and other parts of the Pacific as well as Europe.

They’re most often found in open areas where milkweed plants can grow, though they do spend some time at high altitudes in trees. These butterflies are well known for their migration. They may travel thousands of miles from northern parts of range to southern areas in a single generation. While in southern overwintering sites, they gather in groups and hang from trees at altitudes over 8,000 feet (2,500m). They’ll remain like this through the whole winter until warmer weather prompts them to move in spring.

Not all monarchs do this, though. There are non-migratory groups found throughout the southern parts of their range that remain in the same place year round. Because of these resident populations, monarchs aren’t considered threatened with extinction, however, the monarchs that do migrate are at risk of dying out due to use of pesticides as well as habitat destruction. We may not lose the butterflies, but we may lose the amazing display they put on when they migrate in groups numbering over a billion.

Before heading North, the butterflies breed and lay eggs along the way. They’ll never make it to their original starting point in the north because they die along during their journey and it will be generations later, perhaps their great grandchildren that reach the place they once called home.

The life cycle of monarchs that travel North is shorter than those who make the trip South. They undergo complete metamorphosis in which the eggs are laid on the underside of milkweed leaves. These hatch days later. The larvae go through five instars and eat a bunch while they grow. Their presence is beneficial as milkweed can be toxic to cattle and the butterflies help control milkweed growth. After a few weeks the larvae pupate and form a chrysalis. After another few weeks the adult emerges. The whole process from egg to adult can take less than a month.

As adults, the butterflies drink nectar and help pollinate plants. They only live two to six weeks as adults unless they’re part of the generation that is tasked with heading South, in which case they live a few months and can fly more than ten hours straight a day.

Because they eat milkweed, monarch butterflies and their larvae are toxic to vertebrates. Their bright orange color is a warning of this. Birds generally avoid them, though those that overwinter and don’t eat for months lose their toxicity and may be taken by black headed grosbeaks and black beaked orioles. They may also be taken by rats, ants, spiders, and wasps.

As adults they reach about 4 inch (10cm) wingspans on average. Males and females can be told apart by looking at their wings: females have thicker black veins than their male counterparts and males will have a distinct black spot on their hindwings.

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