Solving the imperfect comb
Honey bees and social wasps developed a similar solution for nest building although evolution separated them 179 million years ago
The combs of bees and social wasps might look similar, but there are differences: bees build with wax, wasps with paper. Bees build double-sided combs that hang vertically, whereas wasps build single-sided combs that hang horizontally.
The perfect-looking structure of the combs also belies an architectural problem: “Not all animals in the swarm are the same size,” says Michael L. Smith, affiliate member at the Max Planck Institute of Animal Behavior and the Cluster of Excellence Collective Behaviour and currently professor at Auburn University. The reproductives can vary in how much bigger they are than the workers. “In some species, it is a small difference, in others, the reproductives are much bigger – and so need a bigger cell to be reared within,” explains Smith.
Predicting the architectural solution
The insects solve the problem of irregular cell size with non-hexagonal cells, which are paired in predictable ways. The most common irregularity is pairs of 5- and 7-sided cells, as the researchers investigated. “We think it’s because there’s a fundamental geometry and perhaps construction method, that results in the particular pairing of non-hexagonal cells,” says Smith. “What's also interesting is that the 5-sided cell is always on the worker-side of the transition, and the 7-side cell is on the reproductive side.”
The research team knew that all the species were going to have to ‘fix’ this problem in some way: “But when we saw that they are all pretty much doing the exact same thing, with some minor variations, that was really exciting”, remembers Smith. “If someone found a totally new species and told us how big the worker and reproductive cells are, we could predict how they would fix that architectural problem, and which ‘tricks’ the insects would use. This would also likely apply to other hexagonal structures, even beyond the social insects.”
The study was possible due to a network of collaborators across the world, who either had photographs of nests from previous work, or were able to get additional photographs.
Hexagonal arrays are used in many contexts, like the wings of airplanes. “The hexagon is a particularly useful shape because it's lightweight, strong, and flexible”, says Smith. “But in some cases, you might want one size of hexagon in one place, and a different sized hexagon in another place for example because one spot needs to be more rigid than another. Currently, the way we fix that architectural problem is just putting a large metal brace on it. Well, the bees and wasps have shown us how this can be done in a smarter way.”