A sepia dun mayfly (Leptophlebia marginata) in Conde-sur-Risle, France. Long an emblem of the summer road trip, squashed bugs on the car have become less numerous over the years, many people say—causing concern about the health of the world's insect populations. While drivers may be happy to have less yuckiness to clean from their windshields, a perceived decline in flying insects hit by vehicles has some experts worried about the creatures, which play a vital role in the environment as pollinators, ecosystem balancers and food sources for other species. But anecdotal evidence is one thing. Studying the so-called "windshield phenomenon" is another. So scientists in France have launched an app-based study that enlists drivers as volunteer researchers. Users download the free app, Bugs Matter , count the number of squished bugs on their number plates at the end of a trip, and send the results to be compiled as part of what the program's creators hope will be a massive citizen science project.…