More trouble for monarch butterflies



Climate change is wrecking havoc on these beautiful butterflies.

So things aren’t looking great for arguably one of the most recognizable and favorite butterflies. Monarchs are migratory butterflies and they spend the winter in Mexico (unlike your grandparents who winter in South Florida). During their winter siesta the monarchs aren’t just sipping away on margaritas they spend their time roosting, where they literally hang onto the tree branches and trunks. These monarchs typically chill out and roost in the Oyamel fir forests and enjoy the moist clouds at about 3000m (~9800ft) above sea level. 

What scientists and conservationists have found is that the roosting area has decreased dramatically this year. Normally the roosting butterflies take up an area of 3-7 hectares, but this year the roosting area is just a measly 1.19 ha (~4.6 acres). So what are some of the reasons why the numbers are declining?

1. Hot temperatures. Remember how stinking hot it was last spring and summer? I certainly do as I was 7-9 months pregnant and here in NC it was hot, hot, hot! The same was true for the rest of North America and hot temperatures mean bad things for caterpillars. Because it was so warm so early the butterfly breeding season was all out of whack. Once the temperature gets over 95F the eggs and caterpillars die, and even at lower temperatures the eggs can dry out. This is actually something that I study in my very own Colias caterpillars and I’ve seen first hand how changes in temperature can change growth and development in caterpillars. 

2. Loss of available host plant. Monarch caterpillars feed on milkweed which was commonly found in corn and soybean fields. An increase in herbicide use and genetically modified corn and soybean (that can survive herbicide spraying) has decreased the amount of milkweed available by over ~50%. There was also a large increase in corn and soybean farmlands that replaced meadows and some conservation lands. Overall, this is a massive loss of habitat, and the monarchs just can’t find enough food. 

3. Loss of winter roosting sites. As mentioned earlier the monarchs roost in fir forests and in these forests there have been reports of illegal logging. Luckily the Mexican government is now working hard to make sure these sites are protected and thus saving the monarchs’ winter home.

Some scientists are concerned that we may have reached a critical low in monarch numbers from which the population may not be able to bounce back. Right now we don’t know, only time will tell how the monarchs will respond to this population setback. It’s stories like these that make me glad that I study climate change and butterflies. While the Colias aren’t in danger of extinction they have certainly responded to climate change in interesting ways (stay tuned for more on my research!) and we are only now starting to understand how increased future climate change could affect them. 

For more information about the monarchs and to see what you can do to help check out Monarch Watch!