A number of simple examples are given:

http://nautil.us/issue/47/consciousness/if-bugs-are-sentient-should-we-eat-them?utm_sou...

"Wasps may strike us as buzzing, sometimes stinging, annoyances when we spend time outdoors. But there’s another way to look at them: as animals with busy brains. Paper wasps, with a brain less than 0.01 percent the size of our own, recognize individuals who are important to them. Neurobiologist Elizabeth Tibbetts discovered this fact when she altered wasps’ facial features by applying modeling paint to them. Nestmates of these suddenly different-looking wasps responded in an atypically aggressive way, while their behavior toward control wasps, who were daubed with paint but whose facial features remained unaltered, didn’t change at all.

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“'Most strikingly,” she and her co-author Adrian Dyer write, “simply removing the antennae from a wasp face image or rearranging the face components dramatically reduced their impressive face-learning capacity.” This fact suggests to Tibbetts and Dyer that the wasps process faces holistically in specialized parts of the brain, as we humans do.

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"Reviewing studies of wasps and bees in general, Tibbetts and Dyer conclude that “there is ever so much more going on their teensy brains than we could have imagined possible.”

"Does that conclusion apply to other insects? Yes, if we’re talking about learning. In entomology, learning is defined as the ability to acquire, and represent in one’s brain, new information. Historically, the working assumptions in entomology were all about instinct. The reigning equation “simple nervous systems = behaviors driven by hard-wired instinct” was straightforward enough—and also spectacularly wrong.

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"In an ingenious experiment, fruit fly subjects were first trained to avoid a certain strong smell, then offered a choice between two samples of that smell whose intensities varied by degrees. The insects took longer to make their choice when the difference in smell was subtle (or minimal) than when it was pronounced (or maximal). Neuroscientist Shamik DasGupta and his team concluded that the experimental outcome “bears the behavioral signature of evidence accumulation.” In other words, these insects wait until they have gathered enough information to make a reasonable choice when presented with options that complicate decision-making.

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"Far more famous an example of insect learning is the honeybees’ waggle dance. In this case, the acquiring of new information happens socially. Performing in the dark hive, the dancers, experienced forager bees, clue in younger, naïve bees about how far to fly, and in what direction, to find suitable flowers. Thanks to scientific experiments, we know that the dances do not operate like the GPS devices that send us, via detailed driving instructions, to a pinpoint location. Instead, they convey information that directs the observer bees to the right general region. There, the flowers themselves provide sight and smell cues; the bees zero in on these beacons and begin to forage.

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"DiRienzio and his coauthors, it turns out, think that crickets use the sounds they hear—or don’t hear—to figure out population density. The crickets who hear nothing assume that they will face little competition from other males in their forays to find females, and act accordingly—asserting greater dominance than they would if they had discerned evidence of greater competition around them. In other words, signals from the surrounding environment alter cricket personality.

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"Generalizing about an enormous taxonomic group of animals is risky. Nonetheless, writing in 2014, Oliver Sacks felt confident enough to offer a summary that resonates with the material reviewed in this chapter: “We often think of insects as tiny automata—robots with everything built-in and programmed. But it is increasingly evident that insects can remember, learn, think, and communicate in quite rich and unexpected ways. Much of this, doubtless, is built-in—but much, too, seems to depend on individual experience.” It’s precisely that unexpected angle that we need to keep our eye on. While it’s far less easy to offer a definitive statement about sentience in insects than about intelligence or personality, insects are surprising us."

Comment: I believe Sacks is correct. It takes a brain to experience stimuli and learn to respond. I've skiopped some exaples in the essay.