Just over a decade ago, scientists working in French Guiana discovered a species of termite that carries a toxic blue substance contained in explosive 'backpacks' which they detonate if the colony is under attack – a form of self-sacrifice found elsewhere in the insect world.
But for years, researchers were unable to establish how Neocapritermes taracua does it. How can the termites safely carry around a dangerous chemical that will nevertheless explode when they need it to?
It turns out that the copper-containing blue crystals, known as laccase BP76, have a number of properties that keep them stable. An analysis of its crystal structure shows that it is tightly folded into a compact shape and that sugar molecules on the outside act as a protective shield. Two amino acids help to maintain BP76’s structure.
Lead researcher on the study Jana Skerlova explains that to trigger the defensive mechanism, the termites must rupture their bodies by contracting the muscles between their body segments, thus allowing the BP76 to mix with labial secretions that dissolve the solid crystals.
“The reaction occurs instantly,” she says. “There are no explosives as such, but the whole reaction is very fast and the toxic liquid bursts out from the termite’s back, killing both the termite and the opponent.”
The 'kamikaze' behaviour of N. taracua (which can be watched in this video) is known as autothysis – which literally means self-sacrifice – and one of its many interesting aspects is the termites get better at it as they age.
As the lead researcher, Robert Hanus, of the original study, published in Nature, said at the time: “Older individuals are not as effective at foraging and nest maintenance as younger workers. In this moment, they can provide another service to the colony.”
N. taracua is not the only termite species to evolve autothystic behaviour. It has been reported in numerous other genera, and though the chemical nature of the substances varies as does the structure of the body parts that release them, the result is very similar.
“In all cases, the released substance is sticky and binds to predators, congealing when exposed to air and causing distress, immobility or death to the target,” reported scientists in A review of self-destructive behaviour in social insects. It is highly effective against other invertebrate predators but much less so against lizards or birds.
This form of self defence has also evolved in other insects such as ants. The Malaysian exploding ant Colobopsis explodens, for example, can rupture its abdomen and release a bright yellow, toxic and sticky substance when the colony is threatened that, reported National Geographic, has a “not unpleasant smell that’s strangely reminiscent of curry” – a discovery to spice up any field biologist’s day.
A Neocapritermes taracua termiteTop image: Dr. Aleš Buček