Trojan horse in an ant nest

It turns out that the protected ant nest, which has constant temperature and humidity conditions and even a food supply, is a place that attracts various insects and animals. Want to know what cunning methods butterflies have developed to penetrate the ants' nest and live at their expense? Butterfly, not what you thought

Article: Dr. Wanda Reich, Young Galileo

Greek mythology tells of the war waged by the Greeks against the city of Troy, which was surrounded by a wall. Odysseus, the leader of the Greeks, came up with an idea of ​​how to penetrate it: the Greeks built a huge wooden horse, put soldiers inside it, placed it outside the walls of Troy and pretended to retreat. The people of Troy saw the Greek army retreating, believed that the horse was a gift from the gods - and brought it into the city. At night, the soldiers came out of the horse, opened the city gates, and allowed the Greek army to enter it and destroy it (for a Trojan horse in the field of computers, see the techno-logical section on page 16).

The truth is that similar tricks developed in nature millions of years before the Trojan War. One example of this is ants. They introduce butterfly larvae into their nests without knowing that they will devour their larvae!

Everyone wants to live in a nest

Even though ants are only two percent of all insect species, numerically they are about 50 percent of the number of individuals of all insects, so ant nests are very available. Unlike the environmental conditions that change frequently in nature, constant temperature and humidity conditions prevail year-round in ant nests, there is a constant supply of food by the workers, and the individuals living in them are usually protected from predators. These improved conditions caused in evolution many species of living creatures (insects, fungi, even frogs!) to develop different means to trick the ants, penetrate their nest and enjoy all the benefits it has. Sometimes even to be treated and fed by the ants.

In response, the ants developed defensive measures against exploitative invaders, and after identifying the invaders, they are immediately expelled or killed. Only those species that were able to develop ways to overcome the ants' detection and protection measures were able to establish themselves in the ants' nests. One of the examples of this is butterflies from the blue-green family.

An ant feeds a butterfly larva?!

Among the 12,000 species of butterflies in the world, about 6,000 species belong to the hornbill family, some species of which (such as the spotted hornbill, the ant hornbill and the cylindrical copper-ant) have symbiotic relationships with ants in varying degrees of dependence. This butterfly is a parasite in ant nests, and is able to complete a life cycle only inside the ant nest and in their care. Its larvae prey on the larvae of the ants, and on top of that the ants eat them!

How does that happen? The female butterfly lays eggs on the leaves of the rhododendron plant, After making sure that there is a suitable surrogate ant nest (only in whose nests the butterfly larvae are able to survive), no more than two meters away from the plant. The larvae that hatch from the eggs feed on the leaves of the plant, pass through the first three instars, and at the end of each larva dangles to the ground with the help of a silken web that it secretes.

At this stage, the continuation of the larva's life and development into an adult depend on ants finding it, dragging it to their nest and placing it in the larval chamber with their larvae. The butterfly caterpillar, which in the first stages of its development feeds on plants, becomes a predator and feeds on the ant larvae! In order to successfully incarnate (become a pupa) inside the ant nest, each caterpillar must devour about 230 ant larvae (!), in addition to the food that the ants eat as if it were their own larva.

In the first month of the butterfly larva's stay in the ant nest, it increases its weight a hundred times. Each caterpillar stays in the ant nest for nine months! Even in the pupa stage, when it is not eating, the ants continue to take care of it. At the end of the incarnation period, an adult butterfly hatches, which quickly escapes from the nest, before the ants have enough time to notice it as a stranger and attack it.  

Perfect camouflage tricks

Ants aggressively guard their nest, attacking and killing any foreign intruder who tries to settle in it and enjoy its benefits. Only a few species that are able to disguise their true identity manage to trick the ants, and settle in their nest.

Communication between individuals in an ant colony is based on the secretion of pheromones. Pheromones are substances that are secreted from an animal into its environment, and are used as chemical signals for communication between individuals of the same biological species. The pheromones secreted by ants are unique to the inhabitants of the nest, according to their status and function. In addition to this, vocal communication takes place based on voices characteristic of the different classes of the individuals in the nest. By these means the ants distinguish between ants from their nest and a foreign invader, as well as the developmental stage, role and status of each individual in the colony. These means of communication are used to carry out tasks in the nest, to recruit ants to collect food or to fight invaders. 

In order for a butterfly larva to be placed in the nest and cared for by the ants, it must disguise its identity and "disguise" itself as an ant larva. This is exactly what is happening. In evolution, these butterflies have developed several adaptations that manage to mislead the ants, and make them treat the butterfly's larva as their own, despite the damage it causes them.

What unique adaptations does the caterpillar of the flute butterfly have that increase its chances of adoption and survival in the ant line? It has a hard body covering that is typical of insects and is 20 times thicker than butterfly larvae from other families. He can put his head under the first joint of the thorax so as not to be injured by the biting mouthparts of the ants while they catch him and carry him to the nest, and later when they handle him.

On top of that, the larvae of this butterfly produce and secrete sugar compounds that are nutritious for the ants that care for them. The sugar compounds are secreted with non-volatile substances that remain on the surface of the larva's body covering. These substances cause the ants to stay for a long time near it, care for it and feed it, sometimes more than their larvae.

Apart from that, the butterfly larvae have special organs near the head. These organs secrete alarm pheromones, which transmit distress to the ants, thus recruiting nurse ants around him.

And you won't believe it - the butterfly larvae secrete pheromones that mimic the pheromones of the ant larvae! In order not to be eaten at the moment of the encounter with the ants and to bring it into the nest, the larva secretes non-volatile pheromones, unique to the host ant species, which mimic the pheromones that the ant larvae secrete, thus providing the butterfly larva with perfect chemical camouflage. The ants treat him as their larva that has come out of the nest, drag him in and place him in the incubation room with their larvae.

Imitating the queen

And what happens in the pupal stage? Another trick: when the entire body of the caterpillar is wrapped in a hard body cover and no longer secretes sugar solutions for the ants, they may stop treating it and endanger its existence in the nest. How does the butterfly caterpillar overcome this danger? The wonder and wonder: he makes sounds that imitate the sounds of the queen of ants, thus causing the ants to crowd around him and take care of the devotion reserved for the care of the queen!

The adult butterfly does not secrete sugar solutions or pheromones and does not make queen sounds, so upon hatching it must quickly leave the ants' nest before they recognize it as an intruder and attack it. Until he manages to escape from the nest, his wings remain folded and covered with a layer of loose scales, these remain in the mouths of the ants that try to bite him, and thus he escapes.

The method of chemical camouflage is not unique to these butterflies. Frog species that live in the savannah in West Africa and other species in the Orinoco and Amazon river basins in South America also use similar methods: they change the composition of the mucus that envelops their bodies in such a way that prevents the ants from attacking them and allows them to stay and even reproduce and raise their offspring inside the protected ant nest, unlike the fate of Other species of frogs, which try to invade the ants' nest - and are attacked.

The author is a doctor of biology, was a lecturer at the Hebrew University of Jerusalem and David Yelin College

From Young Galileo - the monthly for curious children, issue 205 February 2021

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