Some insects, having long gone understudied (only an estimated 10 percent of insect species have even been named, and not in the "I'm going to call this ant Greg" sense), are seeing their numbers drop in ways we've so far only measured with a vague notion of "Hey, our windshields don't get as splattered as they used to when we drive." That's not a joke. Cleaner windshields were a major factor prompting investigation into this matter, because it takes weird developments like that for us to notice changes in the insect world. Bugs still seem endless, so why would we need to count the apparent infinite? But the millions of species of bugs that we never understood are now going away.
This means that bird and fish populations are dropping because their source of food is disappearing. We don't know how far the problem will keep spiraling out, because we've never had the data. Maybe species will go extinct, or maybe they'll suffer the less glamorous but equally serious problem of diminishing, or functional extinction. That's where a species stubbornly clings to life, but at a population too small to be more than a blip on the environment. They become a curiosity, not an active factor.
Functional extinction is a sneaky problem, because it's hard to recognize until we see its cascading effects. We worry about certain species of bears being endangered, but we should really worry about the insects that pollinate the plants that feed the prey that those endangered bears eat. Insects, trillions and trillions of them, quietly make the environment thrive below a level that we normally consider. If they go away, the changes will be subtle but disturbing, a possible slow-motion catastrophe.
The good news is that bugs are resilient, capable of repopulating in swarms if given the opportunity. And growing efforts, like strict pesticide regulations and urban design that integrates insect habitats, are trying to provide those opportunities. Whether it will be enough, no one can say yet. And until we find out, maybe watch where you step on the sidewalk.