The animal world is full of harmless liars, who mimic species more dangerous than themselves in order to avoid the attention of predators. But none do it quite like the dark-footed ant-spider Myrmarachne melanotarsa.
As its name suggests, this small species of jumping spider, discovered just nine years ago, impersonates ants. In itself, that’s nothing special – ants are so aggressive that many predators give them a wide berth and lots of species do well by imitating them. The list includes over 100 spiders but among them, M.melanotarsa‘s impression is unusually strong. It doesn’t just mimic the bodies of ants, but their large groups too.
Unlike all of its relatives, the spider lives in silken apartment complexes, consisting of many individual nests connected by silk. These blocks can house hundreds of individuals and while moving about them, the spiders usually travel in groups. Now, Ximena Nelson and Robert Jackson from the University of Canterbury have found evidence that this social streak is all part of the spiders’ deception.
Ants are among the most successful of living things. Their nests are well-defended fortresses, coordinated through complex communication systems involving touch and chemical signals. These strongholds are stocked with food and secure from the outside world, so they make a tempting prospect for any burglars that manage to break in.
One species of butterfly – the mountain alcon blue (Maculinea rebeli) – is just one such master felon. Somehow, it manipulates the workers into carrying it inside the nest, feeding it and caring for it. The caterpillar does so little for itself that it packs on 98% of its eventual adult weight in the company of ants. How does it do it?
Partly, the caterpillar secretes chemicals that imitate those found on ant larvae, and it mimics their actions too. But that can’t be the only explanation for ant workers will actually rescue alcon blue caterpillars over their colony’s genuine larvae. And if food is short, they will even kill their own young to feed the parasitic impostors. In the entire colony, only one individual is treated with as much respect as the caterpillars – the queen.
Now, Francesca Barbero from the University of Torino has found out how the alcon blues manage to get the royal treatment – they “sing” in the style of queens, producing uncanny cover versions using instruments built into their bodies.