Caedicia simplex

Caedicia simplex is a native insect to New Zealand. Their habitat is limited to that of New Zealand[3] and Australia.[4] While they are not Caedicia simplex it is worth noting that other species of katydid in the shared family of Tettigoniidae are present on all other continents excluding Antarctica.[1]

Caedicia simplex, Common garden katydid

In the original description of Caedicia simplex and analysis of their distribution throughout New Zealand Walker stated that they were abundant throughout the whole of the North Island going so far south as Greymouth, NZ.[3] Today katydids remain throughout roughly those same regions of both the North and South Islands.

Due to the massive distribution of family Tettigoniidae species the habitats can vary highly from nation to nation. Within the context of New Zealand, it is immensely common in-home gardens hence its common name as well as more forested areas.[5] The katydid usually stays near vegetation such as shrubs and plants so that it is able to properly camouflage itself as well as maintain a source of close food/nutrients.[5] Since they are nocturnal katydids usually only move about their vegetation habitats in the night time as this allows for the highest chance of safety and food collection.[2]

It is a common misconception that katydids and other Orthopterans produce sounds by rubbing their legs together. In contrast, males produce the sound to attract females by rubbing its stridulatory file, which is on the underside of the left tegmen, against a raised vein on the underside of the right tegmen,[2] similar to the movement of running a fingernail along a comb. Females in the family Phaneropterinae are unique in the fact that many are able to respond to the male calls by rubbing spines or pegs on their hind wings on veins on the tegmen, but this subject remains largely unstudied.[2]

While the subject of creating sounds is difficult to study in katydids, the subject of hearing is the most widely studied and complex component of katydid biology.[2] The auditory system is highly evolved in katydids, as the neural network receives information from two external sources. The first, a pair of tympanic organs, each comprised to two tympanic membranes, or eardrums, are situated on the tibia of each foreleg on the katydid.[10] The second source of auditory signals comes from auditory trachea, which are evolved from their original respiratory functions, located on the thorax.[10] The physiology of the auditory interneurons of C. simplex has been thoroughly studied and examined by Oldfield and Hill,[11] but requires a high knowledge of Orthoptera auditory physiology to examine.

Katydids and other species in Orthoptera are an important component of many vertebrate diets, such as frogs, lizards, bats, and birds,[2] but the coloration and camouflage that C. simplex has developed and evolved to have, like many species of katydid, put them at an advantage to predators. In addition to vertebrate predators, insects that have been known to hunt and subdue katydids include tachinid flies (family Tachinidae),[12] digger wasps (family Sphecidae), spiders, some species of ants, and many predatory insects that are larger than katydids.[2] Large predatory insects, however, are more of an issue for Australian C. simplex residents, while New Zealand residents have a tougher time with birds. While the camouflage puts katydids at somewhat of an advantage in some respects for predation, Lysaght[13] describes C. simplex as a “sluggish insect”, relying primarily on their appearance to stay hidden from predators.

Gordian worms, or horsehair worms (phylum Nematomorpha)[12] are very commonly found in the abdomen of many katydids as an internal parasite.[2] Gordian worms are a common parasite known for manipulating its host via behavioral alteration, and in the species of one katydid, it was found that this was accomplished by the molecular mimicry of host proteins, which were linked to neurotransmitter release.[14] In the case of many katydids, the parasite did not directly affect an individual’s physiology nor wellbeing, only manipulating the behavior of the katydid at the end of the worm’s life cycle, when it “directs the host to water”, where the worm emerges for a “mating frenzy”.[2]

Species found in Tettigoniidae have a wide variety of foraging methods and diets, such as feeding on dead carcasses or other insects, feeding on pollen, and most commonly, foraging on plants.[2] C. simplex, as well as other species in the subfamily Phaneropterinae, have been observed specifically foraging on plants, but their diet contains a wide variety of such. Primary host plants in New Zealand that have been observed are peach trees, pines, eucalypts, roses, and acacias,[3] and three indigenous species, mahoe, beech trees in the genera Nothofagus, and manuka.[13] Additionally, species in Phaneropterinae have been observed to prefer plants with higher protein content such as flowering species and the flowers themselves, but many are completely capable of developing at a normal rate while only consuming the green leafy matter from plants.[2] While the common garden katydid has the capability to make a sizable impact on gardens, they are not considered an economic threat nor pest.[3]