Heat and regular rains, this is how the year has been with the most mosquitoes in Spain

2020 has been a year marked by the COVID-19 pandemic and an unusual year in terms of the number of tiger mosquitoes. In Spain, twice as many of these insects have been observed than last year, accumulating 1,798 notifications compared to 885 in 2019. The year of the pandemic has turned out to be the year with the most tiger mosquitoes registered by the Mosquito Alert project since 2014. “Densities of Tiger mosquitoes are always explained by two factors, the climate and human behavior, both are those that periodically provide them with water points, where they breed ”, explains Frederic Bartumeus, co-director of the project and ICREA researcher at CEAB-CSIC and CREAF. The 2020 mosquito season started with a warm and rainy spring that allowed them to proliferate during the months of May and June. Furthermore, according to Roger Eritja, entomologist at CREAF and the project, confinement could have played a relevant role in these data, “the ban on traveling to second homes during the months of March and April could affect the maintenance of their gardens, swimming pools and terraces, where the water that mosquitoes need to multiply could accumulate ”, he says.

Tropical summer

This explosion of mosquitoes in spring was followed by a summer that, for the sixth consecutive year, registered higher than normal temperatures, with intense and repeated episodes of rainfall in the Iberian peninsula. The Mediterranean is heating up. The summer is coming sooner, longer and more intense, conditions that can benefit the tiger mosquito when accompanied by regular rains, as has happened this year.

Fig 1. Part of the Mosquito Alert team (John Palmer, Frederic Bartumeus, Roger Eritja) at the Marimurtra Botanical Garden in Blanes where experiments are being carried out with tiger mosquito populations. Source: Mosquito Alert CC-BY


These weather conditions have two effects on mosquitoes. In summer, high temperatures allow the larvae to develop faster, shortening the time between generations, and leading to an exponential growth of their populations. This happens as long as they have places with water to reproduce. On the other hand, global warming, with a warm spring and autumn, could lengthen its seasonality allowing mosquitoes to be active for more days of the year.

Mushrooms, chestnuts and mosquitoes

Autumn is being warm and mosquitoes are still active, as evidenced by the more than 250 reports that the Mosquito Alert platform has received in the last two weeks from Spain, and more than 250 confirmed observations of the tiger mosquito between October and November. In 2019, in the same period, 116 tiger mosquitoes were notified, 9 of them in the month of November, until November 28, 2020 there have been 50 reports of tiger mosquitoes, this is five times more than in the previous year. During November there have been also reports of tiger mosquito activity from Italy, France, Hungary and Turkey. Beyond the temperatures, what most affects the abundance of mosquitoes is having availability to reproduce, that is, having water in the breeding places, either due to the presence of regular rains or due to human activity.

“After having modeled the data, considering the number of users with the application by region and their degree of participation, we see that 2020 slightly exceeds 2015, although their patterns have been very different”, comments John Palmer, UPF professor and co-director of the project. The weather conditions this year have been favorable to the mosquito continuously since spring, while in 2015 its populations exploded exponentially in summer. Understanding the climatic and social factors that determine the dynamics of their populations will allow predicting their abundance in the future.  


A spring with more mosquitoes

The spring of 2020 in Spain has been warm and rainy. The State Meteorological Agency in June announced that it had been the fourth warmest spring in Spain since 1965, with the highest minimum temperatures in the series. In addition to the high temperatures, the season has been as a whole wet, the fifth rainiest spring so far in the 21st century.

The warm and rainy spring has given rise to a greater number of mosquitoes than has been reflected in the observations received in Mosquito Alert during the first semester.

If we compare the number of accumulated tiger mosquito observations received since 2015, it can be seen that the values ​​of 2020 shoot up in May and June (red area) above any of the previous years, in this case 2018, which until today was the year with a season start with more mosquitoes (yellow area indicates the difference between 2018 and 2015). It seems that the rains and heat of the spring weeks created the ideal conditions for the reproduction of the tiger mosquito in the spring. How the season will continue is difficult to say, looking at the previous series it can be seen that 2015 had few mosquitoes at the beginning of the season but its values ​​shot up in August and September. This shows that the spring trends cannot be extrapolated to the evolution of the curve in summer. Taking into account that the biological cycle of the tiger mosquito is very short (about 15 days), the density of future mosquitoes is largely linked to future phenomena related to the availability of water that favor their reproduction.

Spring trends cannot be extrapolated to the evolution of the curve in summer

Another way to analyze the data obtained is to represent the accumulated observations of the tiger mosquito, as in the previous figure, but this time correcting the data, taking into account the sampling effort. The sampling effort is estimated taking into account the number of participants in each area, in this case a 2 × 2 km cell, on a specific day as well as a modeling of their propensity to make observations that day. This correction is important in order to estimate the abundance of the tiger mosquito, it is not the same to have 10 observations in an area where there were 5 people with the app activated, as another with 10 observations but with 20 people with the app activated. To carry out this correction, Mosquito Alert needs to know how many people with the app had this day in a certain area. Obtaining this information is achieved while maintaining user privacy at all times.


Record the position of the device while maintaining user privacy

In order to fit abundance data into models, the Mosquito Alert app collects data on the approximate position of the device from users at random intervals. It is not about exact position data, but they are rounded on the same device to a 2×2 km grid, which is to know that a device is within an area of 2 million square meters. The information obtained by the Mosquito Alert server is that in a specific grid there was a device at that time. The diagram represents in the figure on the left the itinerary of a device throughout a day, where the red points are the moments in which the app collects the position data, after rounding the grid, the server receives the information of the grids in which it was present, red grids in the figure on the right.

To further protect the privacy of users, the locations of the app are linked to a randomly generated identifier that prevents it from being related to any other information that allows their personal identification. Despite the importance of these records in order to calculate the abundances of mosquitoes, users can, at any time, deactivate this function of the app.


Considering the sampling effort, 2020 is the spring with the most mosquitoes in the series

It can be seen that the values of the number of mosquitoes accumulated change with respect to the previous figure, but the trends remain, so even taking into account the number of people with the app activated, the spring of 2020 has been a prolific spring and with more mosquitoes than the previous data series. Until 2020, spring 2018 was the season with the most mosquito registrations, although the season with the most mosquitoes as a whole is still 2015.


The Mosquito Alert researchers want to use these data series from different years to study the effect of climatic variables on the mosquito explosion in spring. Knowing this relationship will allow in the future to be able to make predictions of what the beginning of the tiger mosquito season will be like. The evolution of the season, as previously mentioned, cannot be deduced so much from the previous conditions, but from the future environmental conditions that provide the species with the environments for its reproduction. In order to predict what the start of the season will be, it will be necessary to consider not only spring temperatures and rainfall, but also winter environmental conditions.

The analysis of the data accumulated in the last years will allow in the future to be able to develop the first predictions. Will the day come when we can forecast mosquitoes just as we can with rain or temperature?

Big Mosquito Bytes proposes citizen science and big data as a solution against epidemics caused by mosquitoes

The Big Mosquito Bytes project has been selected within the “la Caixa” heath call. The project will combine citizen science and other massive data sources to develop innovative models that illuminate the risk of mosquito-borne disease in real time. The project, led by CEAB-CSIC, involves scientists from UPF, the Max Planck Institute for Demographic Research, the National Center for Epidemiology of ISPIII and CREAF participate, and draws heavily on the Mosquito Alert citizen science platform.


The “la Caixa” Banking Foundation promotes the Big Mosquito Bytes project with one million euros to help prevent outbreaks of mosquito-borne diseases. The project, led by Frederic Bartumeus, ICREA researcher at CEAB and CREAF, will use citizen science and big data to make real-time predictions of the risk of mosquito-borne diseases like dengue, chikungunya and Zika. “We propose to innovate epidemiology by developing mathematical modes based on real-time data intelligence,” says Bartumeus. The models will incorporate current data on imported mosquito-borne disease cases detected in Spain, along with environmental and climate data and socio-economic and human mobility data. The models will also rely on data from the Mosquito Alert citizen science application showing the distribution of disease-vector mosquitos. The result will be significant improvements in our ability to anticipate the focus of infection and the risk of epidemics, and this will allow more effective entomological and health management. According to Bartumeus, “this improvement in management is the best vaccine to protect the population.”

One of the innovative aspects of the project will be its use of new technologies to study where and how people move, detecting patterns that are important for epidemiological models, and studying how these patterns change at different temporal scales – across days, weeks, or years. Similarly, the project will examine how precipitation and temperature influence the amount of mosquitoes and its biting behavior throughout the year. Big Mosquito Bytes will also use the Mosquito Alert app to learn more about the number of bites people are receiving at different times. The Mosquito Alert mobile application is part of a pioneering system of citizen science in Spain that allows anyone to report the mosquitoes the find by uploading photos. Now, thanks to Big Mosquito Bytes this application will also have the possibility to collect the number of bites received daily, an option so far not available.

Frederic Bartumeus is leading Big Mosquito Bytes


The collaboration between the citizens and the Public Health institutions will allow a greater flow of information and make that one accessible to the population. “Real-time maps will allow better management and better knowledge of the risk of outbreaks of diseases transmitted by the tiger mosquito,” says Diana Gomez-Barroso, an epidemiologist at the National Center for Epidemiology (CNE) CIBERSP / ISCIII. “Big Mosquito Bytes will work mainly on the risks of the tiger mosquito (Aedes albopictus), which is currently the only mosquito that can transmit dengue, Zika and chikungunya, on the Iberian peninsula, but Mosquit Alert is prepared for the detection of the yellow fever mosquito (Aedes aegypti). An even more fearsome transmitter for dengue”, said Roger Eritja, expert entomologist of CREAF.

This is a situation where an important societal challenge can be addressed only with an interdisciplinary team that includes ecologists, demographers, epidemiologists and computer scientists”, said Emilio Zagheni from Max Planck Institute of Demography (MDPIR). For that reason the team led by Frederic Bartumeus will consist of experts from different disciplines: the sociodemographer John Palmer from Pompeu Fabra University (UPF), the demographer Emilio Zagheni from Max Planck Institute for Demography (MPDIR), the epidemiologist Diana Gómez-Barroso from the National Center for Epidemiology (CNE) CIBERESP / ISCIII and the entomologist Roger Eritja from CREAF. Some of them are part of the Mosquito Alert citizen science platform, one of the pillars of the project.


What is the relationship between social inequality and mosquito-borne disease?

One question Big Mosquito Bytes will explore is how mosquito-borne disease patterns are shaped by social inequality and, in turn, end up exacerbating this inequality. The project will examine the ways in which urban design, human mobility patterns, social and economic segregation, and gender inequality influence the distribution of mosquitoes. “This will help us develop ways to reduce the massive and unequal burden that mosquito-borne diseases place on society worldwide” said John Palmer, a sociodemographer at the Pompeu Fabra University.

An idea shared by Emilio Zagheni who considers that “by improving our understanding of mobility and infectious disease dynamics in a scalable way, the impact and relevance of the results will go well beyond the Spanish case”.

Citizen science is a useful and reliable tool for studying the mosquitoes driving global epidemics

  • A study published today in Nature Communications led by researchers at the CREAF, CEAB-CSIC and Pompeu Fabra University shows that citizen cooperation is valuable for studying disease-carrying mosquitos. The study uses the citizen science project Mosquito Alert, supported by Obra Social “la Caixa”, as an example. Researchers from the Universities of Zaragoza and Murcia also collaborated in the study.
  • To study global disease-carrying mosquitos, citizen participation has allowed the researchers to cover much more geographic space in comparison to traditional methods, reducing the economic cost of the two-year study eight-fold.
  • The scientists hope to scale up this citizen science system to a world-wide scale and design new studies on the risk of disease transmission within the contexts of globalization, climate change, and increasing social inequality.
Voluntarios con la app. Mosquito Alert CC-BY

Participants using the app. Mosquito Alert CC-BY


If someone had said to Luis P., a participant of the Mosquito Alert platform supported by Obra Social “la Caixa”, that the picture of the tiger mosquito sent with his mobile phone from Aragon would be a great scientific discovery, he never would have believed it.  The same goes for Jordi S., who found the tiger mosquito in the Catalan pre-Pyrenees for the first time and also raised the alert about its presence using the app. More and more researchers are interested in citizen participation in order to obtain massive data. But is this information of sufficient quality to be used in research? Today, Nature Communications has published a study which highlights how citizen science can revolutionize the monitoring of global disease vectors like the tiger mosquito.

The study, led by researchers at CREAF, CSIC-CEAB and UPF, with the collaboration of researchers at the Universities of Zaragoza and Murcia, shows that when official monitoring and control of disease-transmitting mosquitos is carried out with the aid of the Mosquito Alert collaborative platform, supported by the Obra Social “la Caixa”, the costs and needed efforts are reduced. Using data from 2014 and 2015, the authors calculated that citizen participation with mobile devices reduced the cost of traditional scientific methods by up to eight times. Traditional methods are based on setting traps in strategic areas where female mosquitoes lay eggs.

Map of new tiger mosquito detections in Spain during 2014 and 2015, depending on citizen science source, ovitraps or both. Credits: Palmer et al. (2017) CC-BY

Map of new tiger mosquito detections in Spain during 2014 and 2015, depending on citizen science source, ovitraps or both. Credits: Palmer et al. (2017) CC-BY


Map of new tiger mosquito detections in the Spanish region of Andalucia during 2014 and 2015, depending on citizen science source, ovitraps or both. Credits: Palmer et al. (2017) CC-BY

Map of new tiger mosquito detections in the Spanish region of Andalucia during 2014 and 2015, depending on citizen science source, ovitraps or both. Credits: Palmer et al. (2017) CC-BY


But the real surprise for the scientists was when they confirmed that the citizen alerts made through the app were just as useful as those made by experts for modelling the tiger mosquito’s distribution and predicting its expansion. “The key is to collect information necessary for removing errors and accounting for sampling bias” points out John Palmer, Marie Skłodowska-Curie researcher (the EU programme supporting researchers at all stages of their career) in the Department of Politics and Social Sciences at UPF and first author of the study. The Mosquito Alert platform relies on a team of expert entomologists to validate the citizen scientist reports, which are assigned to categories according to reliability. “Every citizen receives the expert assessment of their photo directly to their mobile phone a few hours after sending it, and this way the citizens learn to recognise tiger mosquito quickly. In a short amount of time we have achieved high quality scientific data, as shown in this study”, explains Frederic Bartumeus, ICREA researcher at CREAF and CEAB-CSIC and director of Mosquito Alert.

The study authors also say that, thanks to citizen science, the tiger mosquito monitoring area within Spain has been expanded. “We now have a large network of volunteers distributed throughout the country who are willing to collaborate with science. This is much better than having to rely on a team of experts who have to travel hundreds of kilometers”, explains Aitana Oltra, scientific coordinator of Mosquito Alert. Beginning in 2014, the project has received more than 3,600 confirmed alerts of tiger mosquitos from throughout Spain, and some of these have been exceptional.ña.gif

Animated daily municipal tiger mosquito report probabilities in Spain using Mosquito Alert app, among April and November of 2014 and 2015. Credits: Palmer et al. (2017) CC-BY


For instance, thanks to the platform’s participants, first sightings were made in Andalucia, the Catalan pre-Pyrenees, Aragon, and Lleida.  What is common to these sightings is that they are in areas far from the coastal zone where the tiger mosquito invasion began.  “The tiger mosquito spreads very fast locally, but also makes long distance jumps; without the help of all of these volunteers raising alerts, it would have taken us much more time to make these key discoveries, especially in remote places where traditional mosquito surveillance tools are not already in place”, says Roger Eritja, entomologist of the Baix Llobregat Mosquito Control Service and head of the team of experts carrying out validation at Mosquito Alert.  All of these early sightings made by citizens have been scientifically validated in collaboration with the Universities of Murcia and Zaragoza, and this will lead to more inspections and the development of country-level public health protocols.

Globalization, climate change and rising social inequalities as risk factors

With new technologies, the scientific world is increasingly connected to people’s daily lives. This connection is vital to address challenges arising from globalization and climate change. “Now we can go even further and calculate the probability that a given person will encounter a mosquito and, as a result, better understand better patterns of disease transmission, and place these patterns in their environmental and social context”, explains John Palmer. In fact, the researchers are already preparing new work to assess the risk of epidemic outbreaks of Zika, Dengue and Chikungunya in Spain using the data provided by citizen scientists using Mosquito Alert. These diseases have an important impact on society and exacerbate problems of poverty and inequality.

Mosquito Alert, increasingly global

Currently, the reports made through Mosquito Alert are an aid to planning pest control measures in areas where the tiger mosquito has been present for many years, such as in the cities of Barcelona and Valencia, as well as in more rural areas such as the province of Girona. Also, thanks to the accumulated experience of studying the tiger mosquito with citizen alerts, the Mosquito Alert team has begun pilot projects in other cities such as Hong Kong (China) and Barranquilla (Colombia). Mosquito Alert also co-leads an international consortium aiming at launching these types of tools to the global scale, with participation of the United Nations Environment Programme, the World Health Organisation, citizen science associations of Europe, America, Australia, Asia and Africa, and prestigious international institutions such as the Wilson Center and Johns Hopkins University in the United States.



John R.B. Palmer, Aitana Oltra, Francisco Collantes, Juan Antonio Delgado, Javier Lucientes, Sarah Delacour, Mikel Bengoa, Roger Eritja and Frederic Bartumeus. (2017). Citizen science provides a reliable and scalable tool to track disease-carrying mosquitoes. Nature Communications8(1), 916.

DOI: 10.1038/s41467-017-00914-9

Sign up for our newsletter to receive all news about Mosquito Alert

Mosquito Alert coordinators