T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network


Dobsonfly (Archichauliodes diversus) NZ Dobsonfly

Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Megaloptera
Family: Corydalidae
Subfamily: Corydalinae
Genus: Archichauliodes
Species: A. diversus
Binominal name: Archichauliodes diversus
Common name: New Zealand Dobsonfly
Common name of larval form: Toebiter, Creeper, puene

Archichauliodes diversus is a native insect in the subfamily Corydalinae. It is the only species of Dobsonfly in New Zealand. The Dobsonfly larva is the largest species of freshwater insect found in fresh water and the only family representatives in New Zealand.
It is endemic and common throughout the country. It is found in stony or hard-bottom streams nationwide in bush covered and farmland areas. It likes live in large, rock pools with an overhanging bush canopy for shelter. It thrives in good quality water.

Archichauliodes diversus larvae are typically 25 millimetres long and have a black, flattened thorax and head. The head has a large set of mandibles. The larvae are sturdy animals with heavily sclerotised heads and thoracic segments. The abdomen is long and light in colour and it has 8 pairs of tentacle-like gills projecting from abdominal segments 1-8. They have anal prolegs with a pair of terminal hooks which they use to attach themselves to substrate, and they lack a terminal filament (the end of the insects ovaries).

Life cycle
A. diversus larvae are aquatic and the adults are terrestrial. It spends most of its life in the aquatic, juvenile stage (2–5 years). The larvae leave the stream between every moult, a unique feature of this species. It has a generation time of more than a year.
The dobsonfly has many stages throughout its life. Changing greatly not only in size but also in appearance as it progresses from egg, larval, prepupal, pupal and imaginal stages. The dobsonfly is nocturnal, mostly active at dusk and at night. The first stage of the life cycle is the egg which is light yellow and cylindrical in appearance and shape when it is first laid. It then turns colour when open to air to a dark brown colour. This stage of the dobsonfly life lasts around 30 days. The larval stage is similar in appearance to the egg, but changes over time when newly emerged. They vary in size, but are roughly around 2.2mm and can grow to around 38.5mm when fully grown. When completely emerged, the larval appearance also changes from an egg to appear more like an insect. It has 8 pairs of ‘gills’ that run down the abdomen which acts as the respiration system. This is the only documented stage during which the dobsonfly eats. This stage occurs all year round. In the third stage the prepupa migrates towards the water edge or water banks. This phase occurs around the months of early July to late January and takes place for 15 weeks. This is due to the water levels being at maximum height as the prepupa needs the soils to be saturated for the next life cycle stage to occur. The pupal stage lasts around 20–24 days. This time frame also depends on the sex of the species, males take longer than females. This occurs around the months of late October to February. Although, the pupa is similar to the adults, it has a bigger build and immature wings. The colour changes in a matter of hours to days, the dobsonfly starts out pale in colour then changes to a dark brown. The last stage is the Imago stage. At this point the dobsonfly is a large insect. An adult dobsonfly only lives for roughly 6-10 days. In this time, they spent most of their time resting in nearby trees. Before the Dobsonfly dies, the female lays several hundred eggs in irregular masses on nearby trees, scrubs, and rocks.

Diet
Archichauliodes diversus larvae are predatorial and use their large serrated mandibles to catch other aquatic invertebrates. This includes Mayfly, Aoteapsyche (net building caddis) and Atalophlebioides (double gill mayflies). They are mostly active at night were they ambush prey around the centre of riffles where there is a lot of oxygen and the turbulence stir up prey. The only stage that the Dobsonfly eats and preys is at the larvae stage and is therefore purely aquatic. At this point the larvae are often the most dominate in the waterways so have little small insect predators. Due to Dobsonfly larvae being nocturnal, they only feed at dusk and night. They are carnivores with the main food source being the mayfly nymphs. They will also eat anything that comes in their way that they can hold with their ferocious jaws; this also includes eating their own species.

Predation
Archichauliodes diversus larval stages is at risk of predation by caddis fly larvae, stonefly larvae, brown trout, Galaxiidae (whitebait). 
The biggest threat to dobsonflies is human intervention, by removing over hanging bush and trees from the waterways. This has a significant negative impact as it is a critical part in the life cycle of the Dobsonfly. The Dobsonfly is only found in good quality water. Any pollution could do serious damage to not only the Dobsonfly but also other species that could be a potential food source. (Scarsbook et al. (2007).

The adult dobsonfly
 v 

The nymph with tentacle like abdominal gills


A nymph's head with predatory mandibles