March 6, 2019
There’s a maxim that nothing good happens after midnight. Like most things in life, it depends on your perspective. If you’re a tasty monarch butterfly egg, it probably holds true. However, if you happen to be a hungry earwig or tree cricket, the party is just getting started. And if you’re an entomology graduate student studying monarch predators, sometimes good research results only happen when you stay up with the nighttime bugs.
The topic of my doctoral dissertation research in Professor Doug Landis’ lab is determining how we can improve breeding habitat for declining monarch butterfly populations. Monarchs have been disappearing across their range for the past 20 years, prompting great concern among those who love this beautiful, interesting insect. One suspected reason for the monarch decline is the elimination of their primary food as caterpillars — common milkweed — from croplands through modern weed management practices.
An everyday observer may notice that milkweed is still a common sight along roadsides, in gardens and in other grassy areas. But compared to 20 years ago, milkweed is now limited to a significantly smaller area. If we want to increase monarch numbers, we have to increase their breeding productivity in these remaining habitats, which is a major challenge for conservationists.
One way that we can potentially produce more monarchs from smaller areas is by increasing their survival during their egg and young caterpillar life stages. Only about 5 percent of the hundreds of eggs laid by each female monarch survive to become butterflies. Most are eaten by other insects and spiders. This brings me back to late night research.
As a first step to my project, I wanted to determine monarch predation rates in grasslands and other types of habitats in agricultural regions. To accomplish my goal, I placed potted milkweed plants with monarch eggs in the field and monitored their survival rates. And because monarch eggs are eaten so rapidly, this work required staying up all night to monitor eggs lost every two hours.
Admittedly, at first, checking eggs all night seemed a bit unnecessary. However, the three nights I camped out at my field site were well worth the exhaustion. I found monarch eggs can disappear rapidly during nighttime hours, pointing to nocturnal predators as one of the main limits on monarch production. But a question remained: Which predator species was responsible?
Last summer, I was able to at least partially solve this mystery. By placing security cameras in grasslands to monitor over 100 monarch eggs, I determined that not only are 70 percent of monarch egg predation events at night, but I could identify the actual predators. The nighttime culprits were earwigs, harvestmen, ants, tree crickets and spiders, while the daytime predators included stinkbugs, plant bugs, mites, jumping spiders and milkweed bugs.
I’m currently publishing the results of these studies. My hope is that this information will be helpful to conservation practitioners in their efforts to create habitats that will help secure populations of this beloved insect for future generations to enjoy.