Monarch butterflies have got to be some of the most well-known butterflies in the world. I remember in grade one our class raised monarchs from caterpillars to adult butterflies, to learn about metamorphosis. I also recall a play we had to do around the same time where I was a butterfly, and my mom made me these ridiculously awesome wings out of cardboard that were way more impressive than anyone else’s in the class (most of them had silly store-bought wings). The point is, that at least for me, monarch butterflies have been fluttering around in my consciousness for pretty much as long as I can remember. So it’s about time I blogged about them.
There are three species of monarch butterfly, the North American monarch, the South American monarch, and the Jamaican monarch. they are found mainly in North and South America, though they also live in Australia, New Zealand and other Pacific islands. Sometimes these pretty travellers appear in the UK, though they usually are there by accident. Monarchs are well-known for their epic migrations, in which millions of butterflies travel south to avoid chilly winters.
Butterfly populations west of the Rockies head down to California for the winter, while those in the east overwinter in Mexico. Those that head to Mexico travel up to 7,778 km to get to their wintering sites — quite an accomplishment for tiny butterflies! This migration is dependent on their being available plants along the route to feed the butterflies, as well as a number of climatic factors, including favourable tailwinds, appropriate temperatures, and low precipitation. If there is an early frost, the butterflies will die.
To try and boost their survival rate, monarchs enter diapause upon commencing migration. This lets the butterflies store essential nutrients needed for the long journey, such as lipids, proteins and carbohydrates. Mating and egg development is also suppressed while the butterflies are in diapause, so they can save all their sexual energy for the spring.
Once the butterflies get to their overwintering sites, things don’t necessarily get easier. If it’s too hot in their roosting areas, the monarch will use up their fat reserves and die before spring comes. Warm temperatures can also stimulate the butterflies to leave the wintering site too early, meaning they will die on the migration back.
This is actually true for all migratory monarch butterflies — none of them survive the migration home. But the successful ones manage to breed before dying, so their descendants can complete the trip home. In fact, it takes four generations of butterflies for the monarchs to get back north.
Monarch butterflies are pretty recognizable with their bright orange and black wings. These bright colours advertise the monarch’s poisonous nature to predators — the butterflies contain toxic cardenolide aglycones, which they get from their diet of milkweed plants. Another orange-and-black butterfly that can be easily confused with the monarch is the viceroy, which was thought to mimic the monarch’s colouring to pretend to be toxic as well. It’s now thought that both butterflies are unpalatable, and that each mimics the other. Nature is confusing…
Most monarchs have wingspans between 8.9 and 10.2 cm wide. Migrant populations have much larger wings than resident populations, as the bigger wings help the butterflies survive their long journeys. Monarchs with larger wings are much more successful during migration.
In recent years, the number of monarchs at overwintering sites has declined. This is likely due to habitat loss, herbicide use and infection by parasites. Though they are not listed as endangered, if this decline continues these beautiful butterflies could be in serious trouble.
Cover image by USFWSmidwest, Public domain, via Wikimedia Commons, cropped to fit