For ants and other social insects, form and function have strong ties. While all the insects in a colony are built from the same basic body plan and share similar genes, the size and shape of their bodies can differ radically according to the roles they play and the jobs they do. Queen ants, for example, are large and winged and are responsible for making more little ants, while the workers are smaller and wingless and keep the colony maintained and fed.
But there’s more to the difference between the two than wings or no wings, says a new study. Workers aren’t just earth-bound versions of queens. Their thoraxes (the middle section of an ant where the legs are) are actually specially suited to their jobs. Meanwhile, the queens’ bodies will come in different shapes depending on the way they start a new colony.
Researchers from France and Portugal used images from microscopes and preserved and dissected ants to inspect the thoraxes of more than 100 ant species, including some that are extinct. They found over and over again that the first section of the thorax closest to a worker ant’s head was enlarged and more muscular than a queen’s. These strong, flexible necks allow workers more strength and mobility when moving their heads and lifting with their jaws—a nice thing to have when you sometimes have to carry home prey that’s 30 to 90 times your own weight. These muscular tweaks, the researchers think, help ants “use to their heads and mandibles in novel ways, and exploit a broader spectrum of resources.”
The researchers also found that two queens can differ anatomically according to how they found colonies. In some species, the queens are claustral, and seal themselves up inside their new nest and raise the colony’s first generation on energy stores from their bodies. Other species have non-claustral queens, which hunt and forage outside the nest to feed the first generation until there are enough workers to take on that job.
In the non-claustral queens, the researchers found large, muscular necks that were pretty close in size to the workers and would give them an advantage when taking food back to the nest. The claustral queens had smaller necks, but larger wing segments. These stronger wing muscles aren’t for better flight, but meant to store more amino acids for feeding the young colony. Looking at the ant evolutionary family tree, including some queens that have “intermediate” body types that are in between these two, the researchers think that as some species became claustral, their queens’ neck muscles got smaller as they became less necessary and the wing muscles had room to expand, making it easier to feed a new brood.