Mimicry in the Rainforests of the Wet Tropics

Skyrail Nature Diary: July 2012

This month we will be looking at the phenomenon of mimicry in the rainforests of the Wet Tropics. Mimicry is the art of looking like another species for a variety of reasons which can be either defensive or aggressive. Defensive mimicry is for the purpose of avoiding becoming 'lunch'. There are seven different types of this defensive mimicry. The first is Batesian mimicry. This is where a harmless animal looks like a harmful one. A good example from the Barron Gorge is the hoverfly. These flies look very similar to wasps which most predators avoid.

Müllerian mimicry involves several harmful animals resembling each other, reducing the risk of mistakes made by potential predators. The best examples of this are the wasps. Wasps all have black and yellow stripes, a feature easily recognised by hungry birds. Mertensian mimicry involves the rare case of deadly prey mimicking less dangerous species. Australia doesn’t seem to have any obvious candidates for this type however in the USA, the deadly coral snakes look like the less dangerous milk snakes. Milk snakes won’t kill their predators but will certainly teach them a lesson. This means that the coral snake will be left alone in future due to it's lookalike appearance.

Wasmannian mimicry is when you like an animal you live with in a colony. This usually applies to ants, termites, bees and wasps. A good example is a Black Katydid (similar to a grasshopper) which looks like an ant who it lives with.

Vasilovian mimicry occurs when weeds look like crop plants to avoid being destroyed. Clearly a man-made form of mimicry.

Gilbertian mimicry is a very rare form of mimicry involving the passionfruit plants. The Heliconius Butterfly lays eggs on the passionfruit’s leaves and the caterpillars end up consuming the leaf and usually more. To avoid this unfortunate outcome, the passionfruit produces structures on the leaves which resemble the butterfly’s eggs, preventing them from laying the eggs on them. In addition to this, the artificial eggs produce nectar which attracts the wasps that prey on the butterfly.

The strangest kind of mimicry however is Browerian mimicry. This involves (as strange as it sounds), resembling your own species! The animals using this method are always toxic but the toxicity within the species varies depending on the strain and the host plant. The natural variety is deleted, reducing the chances of a predator making a mistake and actually eating the prey.

Aggressive mimicry involves tricking prey into thinking they are harmlessm usually by visual cues or sounds.

There are several spiders which mimic ants so that they can enter an anthill and secretly consume some of the inhabitants. These spiders don’t just look like ants, they smell like ants too and coax their victims closer by sending out ant pheromones. Since ants aren’t particularly smart, it never occurs to them that this other "ant" has eight rather than six legs and fangs.....

The Spotted Predatory Katydid (Chlorobalius leucoviridis) of outback Australia is an unusual grasshopper that preys on cicadas. It does this by mimicking the reply clicks of the female, thus attracting the male who ultimately becomes the unfortunate victim.

Mimicry is also used for sexual purposes by a number of plants. Bakerian mimicry is an interesting example of this and is where the female flowers look like the male flowers. This cheats the pollinator out of a reward. It is common to the papaya family.

Dodsonian mimicry is similar to the former mimicry but involves mimicking another plant’s male flowers. This way the pollinator does what is required without getting a reward. The weirdest form of sexual mimicry is Pouyannian mimicry. This is also called pseudocopulation. The flowers mimick the female insect, usually a wasp. It is most common in orchids where the female wasp mimicked is typically flightless and is normally picked up by the male. The orchid flower sends out the right pheromones and the part underneath the stamens look like the basic shape of a desirable female. The hapless male wasp gets snared by the stamens when he tries to take the false female away and has to leave without any mating.

Finally there is the interesting phenomenon of automimicry. This involves part of an organism’s body resembling another part. Some snakes have tails that resemble their heads. Several pygmy owls have false eyes on the back of their heads making the predator believe they are alert to its presence. Some caterpillars have large false eyes on their abdomens to trick predators into believing they are snakes. Although not automimicry, an interesting case of mimicry of part of the body is the death adder’s tail that resembles a wriggling worm. This false worm attracts hungry animals that end up getting eaten themselves.

By Tore Lien Linde