Alexey Polilov reviews* some of the adaptations of the smallest insects. One of the notable consequences of small size is that the reduction in volume and mass is much greater than the reduction in surface area. An insect that is 10-fold smaller in length, will have a 100-fold reduction in surface area and a 1000-fold reduction in volume. That means less volume to store water and accommodate internal structures. Consequently, the thickness of the cuticle is reduced and internal bracing (apodemes and tentorium) may be reduced or absent in the smallest insects. These adaptations may be necessary to accommodate the brain and muscles of the head and body. The weight that must be contained by the exoskeleton of a small insect is less and a much thinner cuticle is sufficient. Many larvae of the smallest insects are parasitoids that are protected by their location inside the host, often swimming in the host’s fluids which buoy further the already tiny weight.
*Alexey Polilov. 2015. Small Is Beautiful: Features of the Smallest Insects and Limits to Miniaturization. Annu. Rev. Entomol. 2015. 60:103–21