If you have noticed fewer monarch butterflies fluttering around the yard this summer, you're not alone. Several butterfly aficionados recently shared their concerns during a Facebook discussion on Monarch Madness in Wisconsin.
Because just 5% of monarch eggs survive to become butterflies, conservation-minded people like Nina Bottomley of Elkhorn is trying to help. She says the number of monarch butterflies she's raised from eggs and newly hatched caterpillars has plummeted alarmingly.
"I went from 124 down to nearly none!" she posted. "What's going on?"
Where are all the pollinators this summer?
PJ Liesch, director of the University of Wisconsin-Madison's Insect Diagnostics Lab, says he's heard several reports of general pollinator activity and numbers — including bees — being down this summer. Unfortunately, reasons for the decline are many.
In early fall, monarchs begin their 2,500-mile migration to the overwintering grounds in central Mexico. The fragile butterflies face ever-changing weather conditions along the way and declining habitat to fuel them for their arduous journey.
Liesch says the eastern monarch butterfly population in Mexico's oyamel fir forests this past winter was nearly 60% less than the previous year. Because counting individual monarchs is an impossible task, researchers estimate the population by measuring the area they occupy (in hectares, which is approximately 2.47 acres). Scientists estimate there are between 20-30 million monarchs per hectare.
"In the winter of 2022-23, butterflies occupied just over two hectares. Last winter monarchs occupied under 1 hectare," said Liesch, adding that this is the first time since the 2013-14 overwintering season that the monarchs have occupied less than one hectare. "If you look back farther into the late 1990s, there has been a definite downward trend over time.
How do extreme weather events impact the success of migration?
Liesch says butterflies across the eastern U.S. heading toward their overwintering ground last fall were met with brutal conditions thanks to a drought that left parched vegetation and fewer late-season nectar sources along waterways.
Monarch butterflies pass through Central Texas on their fall migration south, but this summer’s drought has made the butterflies' journey harder and may change where you'll see them.
"When they fly from the Midwest to Mexico, it's a marathon for them and they essentially need Gatorade, if you will, a carbohydrate source. If you have a drought and don't have many flowering plants, that can make it pretty hard for them," Liesch said.
Droughts during fall migration can also affect monarch lipid levels, which are crucial for overwintering survival and subsequent spring breeding, according to a report from the National Institutes of Health.
Pathogens and predators make life tough for young monarchs
The milkweed plant is essential to the monarch's survival. Adult butterflies lay their eggs on the undersides of the leaves, and when the young larvae hatch out, they begin munching on the leaves, ingesting the toxins from the plant that give them some degree of protection from predators.
Liesch says the black, white and yellow caterpillars, as well as the adult butterflies, are still vulnerable to predation and disease.
"Predators that feed on monarchs can range from assassin bugs and predatory stink bugs to paper wasps, which is a key predator," Liesch said. "If these wasps find a particular patch that has a high density of caterpillars, they can swoop in and pick them off one by one."
The rains during June may have contributed to lush gardens supporting pollinator-friendly plants, but hiding in that vegetation are insect-infecting pathogens, said Liesch.
"There's plenty of these naturally occurring insect pathogens out there, but this moisture can sometimes encourage that fungi or bacteria to kick in," he said.
The UW-Madison entomologist says weather patterns impacted by climate change may affect wider populations of pollinators.
"There are insects associated with specific plants, and if all of a sudden conditions are no longer conducive for those plants to survive, then the insects that rely on them are going to struggle," Liesch said. "Certain plants bloom at different times, and if insects are emerging at a time when the plants aren't at the right stage for them, that could also lead to some complications."
Insecticides are big factor in lower butterfly numbers, study says
While climate change and disappearing habitat appear to play a role in declining pollinator numbers, a study published by researchers from Michigan State University points to insecticides as the largest contributor.
According to the 17-year-long study, co-author Scott Swinton said insecticides — rather than herbicides — are the single largest factor contributing to a decline in total butterfly abundance and species diversity in the Midwest.
“What drives butterfly decline is a hard nut to crack, due to rapid changes in chemical and genetic technologies alongside changes in climate and butterfly habitat,” said Swinton.
The study, which collected data on land use, climate, multiple classes of pesticides and butterfly survey information, was gathered across 81 counties in five states including Wisconsin. According to the study, six different kinds of pesticides, and two types of herbicides, as well as glyphosate, and finally neonicotinoid seed treatments.
The major technological shift in weed control since the 1990s has been the rise and continued dominance of glyphosate herbicides, commonly marketed as “Roundup”. Since the introduction of corn and soybean seed genetically engineered to tolerate this broad-spectrum herbicide, farmers have come to rely primarily on glyphosate for weed control in these crops.
"As a result, farmers increased glyphosate use while reducing the use of other herbicides," Swinton noted. "This became particularly concerning for monarch butterflies since their host plants are strongly associated with row crops and their numbers began a sharp decline during the period of glyphosate adoption."
Researchers found that shifts in insecticide use toward neonicotinoid-treated seeds are associated with an 8% decline in butterfly species diversity across the Midwest. Swinton told WPR that monarch butterflies were especially impacted, with populations declining over 20%.
Ecologist Nick Haddad from the MSU W.K. Kellogg Biological Station and the Department of Integrative Biology said the results of the years-long research is particularly impactful as butterflies play an essential role in pollination and serve as key markers of environmental health.
“As the best-known insect group, butterflies are key indicators of broader insect decline, and the implications of our findings for conservation will extend to the entire insect world,” Haddad said. "Understanding the primary factors contributing to their decline will help researchers working to protect these species, benefiting our environment and the sustainability of food systems."
How can you help support pollinators?
Pollinators are the engine that keeps our ecosystem healthy and our food supply abundant. According to the U.S. Forest Service, over 80% of flowering plants need pollinators to reproduce, and about one-third of the world's food crops depend on them.
So, how can we help them? Here are some tips from the U.S. Fish and Wildlife Service:
- Everyone can do something to help keep pollinators abundant. From a simple window boxes filled with blooms to a few rows of flowers around the edge of your vegetable garden.
- To attract a variety of pollinators, include a selection of plants native to your region. Pollinators need a variety of nectar and pollen sources. Check field guides to find out which plants attract native pollinators.
- Select a site that is removed from wind, has at least partial sun, and can provide water.
- Aim for early and late blooming plants. Selecting some plants that bloom early and others that keep their flowers late in the season helps ensure food for pollinators when other sources are scarce.
- Make pesticides your last option in battling weeds and crop and garden pests.
- Save the stems. Stems and twigs provide nesting sites for solitary bees and other insects. Hold off on pruning and snipping until late spring or just let stems naturally decompose.
- Make your yard or garden friendly to overwintering pollinators. Some butterflies and native bees overwinter as larvae, seeking shelter in leaf litter or by burrowing deep into the ground. And don't be in a hurry to clean out that garden bed in early spring.
Contact Colleen Kottke at 920-517-2653 or [email protected]. Follow her on X (formerly Twitter) at @ColleenKottke.