Painted lady butterfly in the village of Bolonia in southern Spain

More rain in Africa means more painted ladies in Spain

Parvaiz Yousuf

The chicken or the egg? * What came first? A butterfly flapping its wings in China, or erratic weather linked to it?

According to recent research, contrary to what is generally seen in the butterfly effect, the climate, too, can affect migration – at least in the case of insects.

The so-called “butterfly effect” describes how a minimal alteration in the ecosystem could have significant environmental consequences. Coined by Edward Lorenz (a meteorologist), the phrase suggests that even the flapping of the butterfly can cause notable changes in the weather.

Turns out, the weather can determine migration and sustenance in butterflies.

Tale of the happy caterpillar

Migration area of the painted lady butterflies
Migration area of the painted lady. These regions were linked to population abundance of painted ladies in the western section, according to preliminary analyses. Regions outlined in purple are either potential source areas for winter breeding of painted ladies (“tropical forest,” “West Sudanian Savanna,” “Western Sahel,” “Maghreb,” and “Southern Iberia”) or regions where data were collected (green crosses in “northeast Spain,” “Netherlands,” and “England and Wales”). Red and pink points show areas where increases in vegetation are strongly linked to the number of painted ladies seen in spring in northeast Spain. Dark- and light-blue points show areas with a corresponding strong relationship of butterfly numbers with vegetation in February. Image courtesy Proceedings of the National Academy of Sciences. CC BY 4.0

In a study published recently, researchers found that the number of painted lady butterflies (Vanessa cardui) increases considerably in Europe after good rainfall in sub-Saharan Africa. The rains fuel vegetation growth in Africa. The larvae thrive on it, leading to a sharp increase in the number of butterflies that migrate to Europe.

The painted lady is found on all the continents except South America and Antarctica. It is orange with white and black wingtips. In Europe, its population can reach up to 10 million. It migrates from sub-Saharan Africa to Europe and back again. That is a total distance of 12,000-14,000 kilometers.

This migration has had researchers scratching their heads for decades.

“Many myths are associated with it,” says Gao Hu from the Department of Entomology, College of Plant Protection, Nanjing Agricultural University, China, and the lead author of the paper.

Scientists suspected that weather might be affecting the insects’ migration patterns.

“We had butterfly data of around 21 years, which gave us the idea for this research,” says Hu. He stressed the direct relationship between autumn rains during African monsoons and the number of butterflies reaching Europe in spring.

A complex migration

Simulated migration paths for painted lady butterflies
Simulated migration trajectories (paths) across the Sahara. Forward migration trajectories for painted ladies from sub-Saharan West Africa in the spring during three recent years of mass immigration to northwest Europe. The 4-d trajectories were started from each 1° × 1° cell (black crosses) in the west kernel of the Savanna/Sahel region: red lines show trajectories starting from the southern subregion of the kernel, while orange lines show trajectories from the northern subregion on the Sahel/Sahara border. Image courtesy Proceedings of the National Academy of Sciences. CC BY 4.0

Like birds, which exhibit complex migration patterns, insects also migrate over long distances, searching for food or mates. The most famous, of course, is the monarch butterfly, which migrates from Canada and the US to Mexico. In fact, the two species look similar enough to be confused for each other.

Most insects, including lepidopterans, which include butterflies, migrate long distances to avoid the cold. However, unlike birds, they keep breeding through the year as they have short life spans.

“It means that numerous generations complete the migration events, with each generation forming a small [link in the] chain,” says Hu.

Perhaps because they get less attention, the painted lady’s migration was ignored for a long.

“Since the migration events varied year by year, we were assured that some environmental factors [were] affecting this,” said Hu. The researchers saw minimal migration at some times and an explosion in the population at others. They just put two and two together.

Asked about the ups and downs they dealt with, Hu says, “It was never an easy job to do. It took us five years to accumulate the data.”

Our team members already had good knowledge and decades of data about butterflies, although our research was at the mercy of nature,” he says with a smile. He adds that the very factor they were measuring affected their ability to work.

“The unpredictable weather limited our field visits on [some] days, which ultimately prolonged our research, despite the fact that we had enormous data,” he says.

Significance and impact

Painted lady caterpillar
Painted lady caterpillar. Pic courtesy Oriol Massana Valeriano

The study indicates the connection between diverse and far-flung ecosystems and has economic implications.

“Most migratory insects act as pests and damage huge crop matter,” Hu points out, adding that this research has implications for pest control and conservation.

Many insects around the globe are adapting to changing environmental conditions. Moreover, exotic pests are proving to be tough to control. Consider the fall armyworm, which arrived in destructive numbers in Africa in 2016, and India two years later. Hu has studied their spread in China, Japan, and Korea. The researchers are now worried the species can quickly spread to Europe because, as an adult, it metamorphoses into a flying moth.

This study shows how climate change may result in the kind of pest outbreak that Africa and India experienced recently. Droughts or floods can thus impact the number of insects seen.

“We can predict a similar kind of insect outbreak much before it happens,” says Hu. “At the same time, we can conserve important butterfly species that have an important role in pollination.”

Discussion

Painted lady butterfly in the village of Bolonia in southern Spain
Painted lady butterfly photographed in the village of Bolonia in southern Spain. Pic courtesy gailhampshire/Wikipedia

The research could hold some promise for the eastern monarch butterflies, an important pollinator. Their numbers have declined 80% in the last 20 years in North America.

Not only can the species be conserved, but this could also protect the environment.

Every year, large quantities of pesticides are used to control pest outbreaks. This damages the environment and threatens other valuable species.

“This research can aid in population control too, reducing the use of chemical pesticides,” says Hu. He has sought factors affecting insect migrations, in one case even studying the role of geomagnetism.

The team is now trying to find out how these butterflies survive the erratic and unpredictable climatic conditions of the Sahara.

Parvaiz Yousuf is a writer who also doubles up as a researcher. He has publications on cancer biology and biochemistry and has an abiding interest in ornithology.

* Evolutionarily speaking, the egg came first. Chicken ancestors obviously were not chickens. But the eggs were along long before that. Vertebrates have been laying eggs long before the first fish crawled up on land. Arthropods were laying eggs on land even earlier.

Click here for a link to the original research

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