There is a typically telling and intelligent Pixar moment in the film A Bug’s Life in which an already well lubricated mosquito goes up to a bar and orders a ‘Bloody Mary, O Positive’. The barman plonks a droplet of blood down on the bar. The mosquito sinks his proboscis into it, sucks it down in one go and promptly falls over. The main point is that the mosquito doesn’t need a glass because that is for animals that have a problem with gravity. For insects the major force in their lives isn’t gravity at all, but surface tension. The cleverness of the illustrators lies in them seeing this from the perspective of an insect when most of us ignore this kind of thing because our day to day lives are completely dominated by the invisible forces that define not only how we function but the form of our bodies and how we look and behave. As the evolutionary biologist Stephen Jay Gould put it, “we are prisoners of the perceptions of our size”.
The link between form, scale and size is one that defines the natural world. The reason insects don’t grow as large as cows is because then they couldn’t be insects. They are constrained because they have evolved to meet the challenges of the world and the forces that act on them. Surface tension is as great a threat to insects as gravity is to larger animals such as humans because while a human covered in a film of water merely has to carry a pound of extra weight, a fly would have to carry many times its own weight. Conversely an insect falling from the top of a house won’t suffer at all while a person would have a big problem if gravity took hold of them.