What Katydid

Nah, this isn’t about the fictitious tomboy from the 19th century children’s book ‘What Katy Did’. This is about some undoubtedly much more fascinating individuals belonging to the insect family Tettigoniidae. These insects are commonly known as katydids. Katydids are named for the phoneticised version of the stridulous sound they make when they rub their front wings together  – “catedidist”. They are closely related to grasshoppers and crickets and share their basic body shape, see the picture of a katydid below.

Photo by Geoff Gallice, 2012

“What katydid!?” I hear you say. Take a closer look …

Katydids are masters of cryptic colouration and mimicry, in other words, they are masters of camouflage. Insects that can blend in with their environments are favoured by natural selection, they are less likely to be eaten and more likely to reproduce and pass on their genes (and their disguises) to future generations. Camouflage is most effective when the shape and outline of an animal completely merges with their background so they are no longer recognisable, for this to work the animal must stay in a single position for hours at a time. Katydids are very inactive during the day and as a result, relatively little is known about them despite their abundance and variety.

Katydids are mainly found in the tropics but some reside in North America. Most live in treetops or among the leaf litter on forest floors, they are thought to enhance their disguises by deliberately assuming positions that conform to adjacent vegetation. Whilst some species can resemble bark, rock or lichen, those that resemble leaves are by far the most common. As a side note, a study released this month concluded that leaf mimicry could date all the way back to the time of the dinosaurs!

Leaf katydids are probably more common than other types because hospitable leafy habitats are generally much more plentiful than rocky and lichen covered habitats. It’s beneficial if the background against which you camouflage yourself is widespread and homogeneous otherwise you might suddenly find that camouflage which rendered you invisible in one habitat makes you incredibly vulnerable in another.  Another reason many katydids may mimic leaves is because katydids are primarily leaf eaters, there is an advantage in gaining both protection and a source of food from in one place. (Wouldn’t a leaf eating leaf make for a strange sight?).

Katydids themselves are central to the food webs of tropical forest ecosystems. They are a great source of protein for intelligent monkeys who systematically comb through vegetation looking for the camouflaged snacks. When katydids find their disguise has failed they quickly employ their secondary defences: they usually expose brightly coloured hindwings (often decorated with eyespots) to startle predators and some can secrete poisonous or distasteful chemicals to deter them.

Predation is a key driving force in the evolution of camouflage. There is often a self-perpetuating arms race between the perceptive abilities of a predator and the defensive and cryptic characteristics of the hiding prey. If all katydids imitated a leaf in the same way, monkeys would quickly learn how to identify a fake leaf. However, if the fake leaves are as irregular in appearance as real leaves, the monkey’s task becomes much more difficult. It is not surprising then, that katydids do not only mimic one type or form of leaf.  Actually, no two individuals are exactly alike within a single species; some may look dead, some discoloured and some even look partially eaten!

Katydid variation may result from differential expression of pigment encoding alleles and other genes related to mimicry, possibly promoted by external stimuli or due to the inheritance of new combinations of alleles through genetic recombination. The variety of katydids is reflected in the fact that the same species have been discovered and described more than once under different names.

Photo by Jenny Miller, 2013

Of course katydids aren’t the only animals or indeed the only insects which successfully employ camouflage in their survival strategies – stick insects are perhaps the first example to come to mind. Nevertheless, for me the precision of the leaf katydid façade, as well as being visually extraordinary, is a spectacular representation of the effects of evolutionary adaptation. Even with some knowledge about the underlying mechanisms of their disguise they never fail to impress me and this is why katydids are some of my favourite insects.