Revealing the effect of brain size on the cognitive abilities of animals is a major challenge in the study of brain evolution. Analysis of the effects of miniaturization on brain function in the smallest insects is especially important, as they are comparable in body size to some unicellular organisms and next to nothing is known about their cognitive abilities. We analyse for the first time the structure of the brain of the adult featherwing beetle Nephanes titan, one of the smallest insects, and results of the first ethological experiments on the capacity of learning in this species. N. titan is capable of associative learning, in spite of the structural modification in its nervous system and the greatly reduced number of neurons compared to the nervous systems of larger insects. Microinsects can become useful model organisms for neurobiology. On the one hand, the structural simplicity and extremely small size of their central nervous system make it possible to study it very efficiently. On the other hand, their learning capacity and retained principal cognitive abilities make them suitable objects for behavioural experiments.