Many social insects, like ants and termites, do most of their work with their mouths. After enough time spent cutting through foliage and shoring it around, the mouth parts on older animals tend to wear down and lose their sharpness, making them less able to contribute to their nest. Now, researchers have found the way that some older termites can remain useful to their peers: they become suicidal chemical weapons specialists.

The authors were working with a species that was already known to have a penchant for a suicidal form of defense. When confronted by a competing species of termites, the animals tend to burst, releasing a sticky substance from their backs. However, the authors noticed that a subset of animals had blue stripes across their backs, and were far more prone to bursting with just a bit of minor prodding from an enemy termite.

They did a pair of parallel measurements and found a strong correlation: as the animal's mandibles wore down with time, the amount of blue coloring went up. This suggested it was slowly being produced over the animal's lifetime, and gradually accumulating under the cuticle on the insect's back. Perhaps more significantly, the blue goop that poured out of the insects when they burst was more toxic than the white liquid loosed from younger termites.

The authors isolated the blue substance and purified a copper-binding protein from it (which explains its blue color). And they discovered that the termite species in question has a small gland at the junction between two body parts (the thorax and abdomen), dedicated to producing the toxic substance. It ends up stored just below the surface of the animal's cuticle, ready to burst out when it's bitten.

The authors start their article with a quote from E.O. WiIson, who wrote, "We send our young men to war; ants send their old ladies." But, from an evolutionary standpoint, those old ladies aren't working as well as they used to, and exploding into a blue froth can do a lot to defend them.

Science, 2012. DOI: 10.1126/science.1219129 (About DOIs).