Summer and creepy crawlies: drought causes problems for insects

dpa | Dry summers affect many insects in Germany. This year too there was far too little rain in the warm season. Some species lack water sources for laying eggs, others lack moist meadows for foraging. But some also benefit. A look at the situation with mosquitoes and butterflies.

Many people in Germany may have had fewer itchy mosquito bites this summer than usual. “From the mosquitoes’ point of view, the summer went badly,” says mosquito expert Doreen Werner from the Leibniz Center for Agricultural Landscape Research (ZALF) in Müncheberg, Brandenburg. There were significantly fewer local mosquitoes around than in other years.

Native species like it moist and warm. But this summer there was far too little rain. “Where there are no breeding grounds, there are no mosquitoes,” says the biologist.

Mosquitoes lay their eggs in stagnant or slow-moving water, such as ponds, watering cans or rain barrels. The rain barrels were filled, says Werner. When it rained, the rain came down so hard that the eggs and larvae were often washed out of the bins.

However, a bad year for the animals does not mean that things will continue to get worse for them. “The mosquito can lay multiple broods, each with between 250 and 300 eggs,” says the biologist. “A population that has been shut down can rebuild itself relatively quickly.”

The local mosquitoes are still active now. The larvae continued to hatch into October. “They still sting, but there is no longer an increase in occurrence.” The animals were preparing for hibernation. "Now in the fall, a lot of house mosquitoes come into the living area. They are looking for a place to overwinter that is frost-free."

According to the expert, things looked completely different with the invasive species than with the native mosquito species. “The tiger mosquito and the bush mosquito are conquering Germany,” says Werner. The high temperatures played into the animals' hands.

Together with the Friedrich Loeffler Institute, ZALF runs the so-called mosquito atlas. Citizens can send in mosquitoes they have caught, which will be scientifically identified and examined for pathogens. Werner said she received a lot of tiger mosquitoes this year, especially from southern and central Germany. The finds are constantly increasing.

When it comes to butterflies, the results are mixed, as agricultural biologist Josef Settele from the Helmholtz Center for Environmental Research (UFZ) explains. When it comes to butterflies, there have been twice as many losers as winners in recent years. Moisture-loving species in particular are doing poorly due to the drought. “The decline in some species is striking.”

According to Settele, there are around 3,700 species of butterflies and moths in Germany, including almost 200 species of butterflies.

Species that feed on herbs in meadows would also have a difficult time. “When we looked at the grassland this year, many meadows and pastures were no longer green due to the drought.” Butterflies that suffer from this and have declined sharply are the meadow blue ants. The butterfly only lays its eggs on the Great Meadow Button. According to the biologist, the plant grows in alternately moist to wet meadows and is less common in dry conditions. The caterpillars also overwintered in ant nests, which required moist conditions all year round.

Some heat-loving species, on the other hand, benefited from climate change and continued to spread, according to the expert. An example is the sail butterfly. “It used to be a very rare, highly endangered species.” The cream-colored butterfly with black stripes is now doing very well. “It flies in our garden, which is actually quite unusual.”

The butterfly has the advantage that it feeds on plants and bushes that have deeper roots and are therefore less susceptible to drought.