Just over 10,000 times, scientists armed with a mechanical swatter and high-speed cameras tried to swat mosquitoes out of the air. And in only 8 percent of the cases this was successful.

Wageningen researchers have noted that terrible success rate in the magazine Current Biology†

The experiment

The scientists came up with this after experiments with two types of mosquitoes: the malaria mosquito (Anopheles coluzziiwhich is mainly active at night) and the yellow fever mosquito (Aedes aegyptian, which is active during the day). Both species were released into an enclosed space, where they could fly freely. In that same room, however, there was a mechanical mosquito swatter that regularly tried to swat the mosquitoes out of the air. “That swatter is about the size of a human hand,” says researcher Antoine Cribellier. “And also moved about as fast as a hand. At the same time, there are of course also differences between a hand and our mechanical swatter,” he says. “The swatter has no fingers, a different color and can only move in a straight line. Also, the movement of the swatter during the attack cannot be adjusted, while a human being during the swat will probably try to change the course of the hand and thus chase the mosquito.”

Cameras

While hunting for a mosquito is guided by the sound it makes or where we see it, the swatter also has to do without eyes or ears. But how can he know when to hit? The researchers have come up with something for that too. “In our experiments, we used five cameras in real time an estimate of the position and speed of several mosquitoes flying around. And based on that, we could predict where mosquitoes would fly in the future. When it was predicted that a mosquito would fly through the center of space (and thus come within range of the swatter, ed.), the mechanical swatter was automatically activated.” Success guaranteed, you might think. But nothing is less true. Because of the 10,000 attempts that the swatter made to knock a mosquito out of the air, only 8 percent were successful.

Air movement…

So there’s nothing to be ashamed of if you’re slacking around fruitlessly and desperately this spring or summer. But why is it so difficult to knock a mosquito out of the sky? On the one hand, we are probably to blame for this. “It seems intuitively very likely that mosquitoes are pushed away by the airflow generated during an attack,” Cribellier said. “But there is no published scientific evidence for that yet. I am now also working on an article about this, but I can’t say much about it yet.”

…and more

But even if follow-up research shows that we swat mosquitoes generate an airflow that helps the mosquitoes to escape from us, that’s not the whole story. Because during the current study, researchers saw something special happen. The malaria mosquito – which was active at night – managed to escape much more easily in the dark than during the day. “We know that mosquitoes use visual cues to recognize attacks,” Cribellier said. “But of course these clues are missing in the dark. The animals may simply be swept aside by the air movement of the swatter, but that should be the case both during the day and at night.”

But that’s not what the researchers saw happening. Because the malaria mosquito, active at night, was more successful in escaping the swatter at night than during the day. And the yellow fever mosquito, active during the day, managed to escape more often when it was light. It strongly indicates that the mosquitoes themselves have also developed a strategy to avoid being knocked out of the air, and that strategy is completely adapted to the conditions under which they are active (dark night or during daylight). This is further endorsed by their flight behavior prior to each attack. For example, malaria mosquitoes have a very irregular flight pattern in the dark. This made it harder to predict where they would be in a few seconds, making it more difficult to knock them out of the sky. Meanwhile, the yellow fever mosquito appeared to have a much more predictable flight pattern during the day, but again to be much more adept at escaping. “This proves that both species have adapted their flight behavior in such a way that their escape attempts are most successful under the conditions in which they suck blood, and thus are most often exposed to attacks from their host,” said researcher Jeroen Spitzen.

Follow-up research

The research provides more insight into how mosquitoes manage to escape from us. But the study also raises new questions and hypotheses, says Cribellier. “It was particularly surprising to see that malaria mosquitoes were able to perform escape maneuvers in the pitch dark. We therefore wonder whether these maneuvers are only the result of the air movement or whether the mosquitoes are able to detect the attacker – without being able to see it. If the latter were the case, it would of course be very interesting to find out how they detect the attacker. We are also very curious how we can use these results to improve mosquito traps. In previous studies, we have studied the behavior of mosquitoes around these traps developed in the fight against malaria. And we found that the mosquitoes were able to escape the trap by flying away from the area from which they would be drawn into the trap. This new study — and the next — may provide more insight into how they do that.”

For now, the research already seems to provide some handles for anyone who will start the hunt for invaded mosquitoes next summer – against their will and thanks. “We show that mosquitoes (that are active at night, such as the malaria mosquito, but perhaps also the common mosquito, ed.) rely heavily on their unpredictable flight patterns to avoid being hit. This strategy is probably common in the animal kingdom, but has often been neglected. In the case of the mosquitoes, it means that – if you want to swat them out of the air – it’s good to take the time to make an accurate prediction of their future location and then strike quickly – before they have the time to deviate from that predicted location.”