They are great strangers for the human being. Only in Spain have been described up to 40,000 species of insects and each year 200 more are added to the list. Bees, bumblebees, flies, butterflies, fireflies, beetles … And, despite this ignorance, scientists have no doubt that many of these species are in decline in the world by human pressure. The question is, to what extent the situation is as catastrophic as some studies estimate. Because data and historical series are missing to compare.
The debate over the real state of the populations has intensified after the publication of a research from the University of Sydney (Australia) in the scientific journal Biological Conservation, that was collected by countless media in the world. The authors of the study, Francisco Sánchez-Bayo and Kris A.G. Wyckhuys, conclude that more than half of the planet's species are rapidly declining and one third is threatened by extinction. Some data that make fear that more than 40% of the species of insects extinguish in the next decades. Butterflies and moths would be among the most affected by this threat.
But, while decreases are appreciated, there are redoubts -in well-conserved areas- where these arthropods are safe and scientists that move away from the catastrophic vision provided by the aforementioned article. The ecologist of Superior Council of Scientific Investigations (CSIC) Carlos M. Herrera has proven, in 29 plots and during the last 20 years, the evolution of the pollinators of areas undisturbed by the man of the Sierra de Cazorla, in Jaén. During those two decades he has meticulously noted which flowers were there, who visited them and for how long. It has gathered three million records of 65 species of plants and about 600 pollinators. And the data collected allow you to ensure that in these places the insects object of your study have increased. With these results, Herrera argues that changes in the abundance of pollinators "may be due to very complex dynamics", so generalizations based on modest sampling should be avoided. They need "powerful analytics, not limited to particular groups of plants or pollinators," he says.
For Javier Alba-Tercedor, professor of Zoology at the University of Granada and expert in aquatic insects in the Sierra Nevada, "there is no doubt that we are attending a great extinction, but insects have demonstrated over millions of years their ability to adapt to changing conditions. "This ability to adapt is caught by this researcher to be optimistic and reject the insects will" disappear from the face of the Earth " But this does not mean that Alba-Tercedor asks for action to avoid the negative impact of human activity on these types of animals.
Share the same perception Jorge M. Lobo, CSIC researcher specializing in beetles, who advocates developing protocols that allow sufficient data to be collected on insect populations in similar ways in different places over long periods of time. It would be "to build a system similar to that used by the meteorological services, which collects data continuously and allows to obtain constant information". Because, Lobo adds, "if insects are falling, the first thing that should be addressed is the preparation of a real census." In 2011 there was an attempt to collect data from the State that was reflected in the Red Atlas of threatened invertebrates in Spain. The publication gathers news about more than 200 insects. But until that point arrived, the project has not been continued or updated.
A few weeks ago, a group of scientists signed a decalogue for the conservation of wild pollinators in the Iberian Peninsula. They propose to increase the availability of flowers, reduce the use of pesticides, legislation that protects the most sensitive species, improve the environmental education of farmers and promote research and knowledge about insects. "The truth is that we still do not know the conservation status of much of that fauna," they complain.
Despite the lack of a complete portrait, some cases in which sufficient data exist on the decline are alarming. These are some of the most prominent.
Bumblebees | Extinctions in the Cantabrian mountain range
The situation of the bumblebees is complicated: 70% of the species are classified as threatened or with decreasing trends in the population by IUCN. The contribution of this group of insects to pollination tasks is very important, given that they are capable of self-regulating body temperature and withstanding the cold climate that prevails in mountainous systems. Some areas that are especially sensitive to temperature changes and that have become a kind of natural laboratories where climate change can be studied.
In Spain, a study on pollinators by José Ramón Obeso, professor of Ecology at the University of Oviedo, has recorded the complicated moment that bumblebees have been crossing the Cantabrian mountain range a decade ago. There are 24 species in the area, including some with severe conservation problems in Europe, as is the case with B. cullumanus.
Research indicates that some of the families "seem to have become extinct," although most have gone up in average altitude. The disappearance of specimens was detected mostly in low (up to 900 meters) and medium (between 900 and 1,500). From that height, colonizations increase. Not only that, but the generalist bumblebees (with greater adaptability) are more abundant in these environments, to the detriment of more sensitive ones. This has caused a homogenization of the species, whose consequences on the pollination of the plants are still "far from being clarified".
Bees | The most efficient and profitable pollinator
Bees are one of the most efficient and popular pollinators along with bumblebees. Of the 1,000 species that exist in Spain (20,000 have been described in the world), the International Union for the Conservation of Nature (IUCN) considers that 2.6% of them are threatened. But the number could be higher, say the experts, because "of many there is not enough information", so much so that in Europe the state of 56.7% is unknown. "Its decline is due to multiple factors," explains the scientist Cristina Botías. But within this cluster of causes are the loss of habitat, emerging infectious diseases, exposure to pesticides and competition with bees that come from beekeeping operations and that destabilize natural balance, in addition to climate change.
The consequences of its disappearance would be serious: In Spain, 70% of the main crops for human consumption depend on insect pollination. So it is estimated that its fall could mean a reduction of between 40% and 16% of fruit and vegetable crops.
Ignasi Bartomeus, CSIC scientist and bee specialist, believes that "not everything is lost if the current trajectory is changed". Their conclusions are based on a study published last year in which they compared the historical records of a thorough investigation conducted in Valladolid in the eighties with the current situation. "In natural localities near Hornillos and Olmedo the population has remained stable, but in transformed areas near Valladolid, Zamadueñas or Toro more species have been lost," he explains. Therefore, "it does not depend on the municipality, but on the transformation of the habitat". That's where you have to focus your attention.
Butterflies | Some fly higher, others disappear
In Europe, 17% of butterfly species are threatened, 10.1% are on the way to being and diurnal species face declines of 30%. The scientist Constantí Stefanescu coordinates the Catalan Butterfly Monitoring Scheme (CBMS), a monitoring network with more than a hundred stations in Catalonia, Andorra and the Balearic Islands. Stefanescu points out that 70% of the species of common butterflies that have followed are in regression. One of the most affected is the Melanargia occitania, that in the last 25 years has experienced an "alarming" decline. In all the towns with populations collapses and even some extinctions have been observed. Their problems are due to the modification of the habitat with irrigated crops and loss of sheep grazing that causes an increase in the scrubland. Another example of butterfly in distress is the Parnassius apollo, known as Apollo. Emblematic of the National Park of the Sierra del Guadarrama (Madrid), has risen in 40 years from 980 meters (its lowest distribution) to 1,450, and the highest place where he lived at 2,040 meters has climbed to 2,250. The average temperature increase of 1.3 degrees in 46 years is behind the changes, explains Juan Vielva, head of the Research Center.
Some species like Libythea celtis, the butterfly of the hackberry, they demarcate themselves from the tendency. In the last three decades this butterfly (with a reputation as rare in the middle of the last century) has become common in many parts of Catalonia. It has colonized Barcelona and in 2018 there were concentrations of hundreds of individuals, especially in the mountains. Human activity, in this case, has been positive, by planting hackberry in many towns and cities.
Beetles | Antiparasitics turn them into zombies
Most of the more than 200 species of dung beetles in Spain are endangered by the exaggerated use of antiparasitic agents for livestock, explains José M. Lobo, CSIC scientist. The best known is ivermectin, which causes them difficulties in moving or flying and a weakening of the immune system, which makes them more vulnerable to attacks by fungi. "The lower doses of the antiparasitic that are in the field are insufficient to cause their death but they become zombies," says Lobo. There are still redoubts where they escape danger, such as Doñana, where you can not administer such products to animals, or in the Cabañeros National Park, where there are no livestock.
The mission of these coleoptera is vital for nature because they make disappear the excrements of other animals so that they pass to the ground, favoring that the ground is nitrified and aerated. In addition, infection by parasites that can be generated by the excrement is avoided if it does not disappear. If these insects decrease or disappear, the boñigas accumulate in the field, the parasites reach the grass and when the cow eats it, it becomes infected. "This is already happening in areas of the Picos de Europa, for example, where small mounds are seen, which are old excrements, covered with grass that is of lower quality."
The solution, says Wolf, is simple. "You just have to apply the logic and administer the medicine to the animals at the times when it is necessary," explains the researcher. In the case that specimens with high doses of parasites are detected in a livestock farm, it is best to separate them from the rest and bury the excrement.
Water insects | Trace the channel to escape the heat
Scientists of the University of Granada have verified that the aquatic insects (trichoptera) of the rivers of the national park of Sierra Nevada (Granada) have moved in the last 20 years upstream, escaping the temperature increase of almost two degrees attributed to the change climate. The research showed that these species are very sensitive to the rise in temperatures, in addition to being excellent bioindicators of the existence of good environmental conditions.
Professor Javier Alba-Tercedor, from the research group and professor of Zoology, explains that if the warming continues, "many species will disappear because there will come a time when they will not be able to migrate higher when they reach the summits." In addition, competition phenomena will arise due to the appearance of new settlers that are also rising, and this makes the permanence of endemisms (species that are only there) that harbor the high mountain rivers of the Sierra Nevada more complicated.
The worst scenario arises for the families of these invertebrates that live near the mountain tops, which face the additional risk of extinction by not being able to continue climbing. Therefore, it is expected that aquatic insects from headwaters experience a reduction in their distribution area, while they are progressively replaced by medium or low river species and by other generalists that adapt better to the changes.
To arrive at these conclusions, the researchers compared the current temperature and flow conditions of the water courses of the Sierra Nevada mountain range, with which other studies of past decades were measured.
Crickets and grasshoppers | Agriculture and urbanism cut their wings
It is not a sensation, it is a reality: The usual cri cri with which the cricket enlivened the summer nights threatens to become a rarity. In Europe, a quarter of species of crickets and grasshoppers are threatened by human activities such as agriculture or urban planning. Their condition could be worse, given that data are still lacking, according to an IUCN research that studied 1,082 species of Orthoptera, the scientific name of that group of invertebrates. It groups more than 1,000 species in Europe that perform important functions in the ecosystem, such as being part of the diet of many vertebrate species.
Of the 739 endemic species in Europe, 231 are endangered. Of these, most are concentrated in the Iberian Peninsula, the Balkans and mountains such as the Alps, the Pyrenees, the Carpathians and the Apennines. The European areas with the greatest diversity of these animals are in the south of the continent, especially in the Mediterranean, which also concentrates some of the most vulnerable.
The main threat they face is the loss, degradation and fragmentation of their habitats as a result of the intensification of agricultural use, which converts pasture land or scrubland into farmland. Added to this is the degradation caused by overgrazing, the use of fertilizers or heavy machinery and direct mortality from pesticides, as well as tourism development and urbanization.