The Dobsonfly "The King Bug"



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Introduction

The Dobsonfly is not one of the most well known insects in the world, however it populates a vast expanse of it. The average response upon finding this creature is usually screaming, jumping and the occasional fall. The mean looking mandibles are actually rather harmless though, and the Dobsonfly is beneficiary to the environment around it. The species are certainly not rare, just hard to find. Their nocturnal nature and short lifespan make them a tricky catch. It is only appropriate for one to be fully informed on this insect, for they are not just your average butterfly.

Morphology


The Dobsonfly is easily distinguished by its long slender appearance. It is usually dark brown with black and grey markings, lighter Dobsonflies are not uncommon however. They are known to grow up to 5 inches long, from mandible to the end of the folded wings. These wings can be up to double the length of the body. Large mandibles are common in males, and shorter pinchers are found in females. The antennas of the Dobsonfly are long and sweeping and as seen in the picture above, and are often segmented. The body of the Dobsonfly has a twig like appearance, combined with a brown body scheme color, it blends in well to forest floors.
The Dobsonfly spends most of its life as a larvae. The adult cycle of it's life in fact, is only a fraction comparatively. Up to one to five years are spent in the larvae cycle for the Dobsonfly. This stage usually occurs in fresh water streams. The stage after hatching from eggs cells is the Hellgammite stage. This creature looks like the first in the image below, it scurries on the stream bottom hunting for food. During the time between adult and Hellgammite the Dobsonfly goes into a pupa, or the stage of morphing into an adult. A commonly known form of this type of change is butterfly metamorphosis. When the hellgammite is ready to enter this stage it stays close to the water, staying on or near the shore. They stay in between stages for several weeks. The cocoon insulates them from the frigid temperatures that exist mainly in the climate of the Eastern Dobsonfly which thrives in North America. The hellgammite has no silk weaving abilities so it creates a basic cell underground which protects it. When it sheds for the last time, the cocoon is complete.The adult life of a Dobsonfly is rather short lived compare to it's existence as a larvae. As a fully grown adult the Dobsonfly only lives for several days. It is at this time that they lay their eggs and make way for a new generation.

Eastern Dobsonfly life-cycle - Corydalus cornutus - male - female
Eastern Dobsonfly life-cycle - Corydalus cornutus - male - female


Habitat

Dobsonflies usually live in rocky streams. It is important that the streams are not all comprised of silt because larvae they attach themselves to the bottom of rocks for feeding and protection from predators. They are very adaptable to climate, living in a range of continents from Asia, to South America and North America. The Eastern Dobsonfly in particular lives in a mild climate. In the Geographic Range section, one can see that the Eastern Dobsonfly lives from the Colorado Rockies all the way to Maine, and parts of Canada. There are very few places in this world where the Dobsonfly cannot survive. A key factor in the survival of the Dobsonfly when it comes to habitat, is the existence of other aquatic insects. The Hellgammite population must be able to thrive off of eating other little insects. The fresh water streams that the Dobsonfly is born from must also not be to shallow. Since the majority of the Dobsonfly's life is spent as a Hellgammite, one drought could kill off the majority of the population.
external image Rocky%20Stream.jpg

Geographic Range

The Eastern Dobsonfly(Corydalus cornutuslives) lives mostly in the Eastern region of North America. Dobsonflies in general can be found in great variety from Mexico across Central America and into South American countries such as Brazil or Argentina. Our scary looking friends also appear in Asia. They inhabit parts of China, Japan, Vietnam and Indonesia. The vast range of places the Dobsonfly lives in is due to its ability to survive seasons well. The Dobsonfly can survive winters when cocooned in the earth, during it's pupa stage. During hot summers the Dobsonfly is most likely a Hellgammite which has a regulated climate due to it's environment being in water and under rocks. During the adult stage Dobsonflies live a very short life, so any extreme conditions would have to kill this insect within a week to make any impact on it's thriving in that location.


Range map for Eastern Dobsonfly
Range map for Eastern Dobsonfly




Mating Behavior

 Dobsonfly - male - Corydalus - male
Dobsonfly - male - Corydalus - male

A common mistake in observing the Dobsonfly is to assume the male uses his hook like jaws for eating. The Large mandibles found on males are not for eating but rather mating. They allow the male to hold on to the female and are also thought to be apart of male "jousting" which is when males compete for fertilizing a females eggs. The pinchers on females however are able to bite prey and any unlucky human observers. Dobsonflies only mate when they are matured adults which is only a range of just under a week. Most Dobsonflies stay near where they were born to mate. Often times bright lights distract these nocturnal insects, leading them to their death. In any case though, both male and female will die after all the eggs have been fertilized. The eggs are usually found on logs or rocks overhanging a fresh water stream. The white substance that covers the eggs (seen below) is thought to keep them from overheating and protects them from predators.
A brief summary of the little known mating behavior of the Dobsonfly goes as followed. A egg hatches from which a Dobsonfly larvae emerges, which is essentially a small Hellgammite which grows. After several years of feeding the Hellgammite emerges from the water to go into the pupa stage. Weeks later it is an adult. If it is male it will seek a female and if it has to, joust off another male to fertilize her eggs. If it is a female, her eggs will be fertilized and she will lay them on an area close to a stream so the Hellgammites can be born and the cycle starts over again.
Dobsonfly Eggs
Dobsonfly Eggs



Life Cycle

The Dobson fly spends the majority of it's life in the larvae stage. During this stage it is called a Hellgammite. In the Hellgammite stage the Dobsonfly lives underwater. It will shed it's exoskeleton anywhere from 10 to 12 times when in this environment. It is in this part of their life cycle when the Dobsonfly larvae feed the most. When they are ready to pupate they leave the water or travel up to 15 meters to find a suitable location. As it digs it's own cocoon the hellgammite sheds its skin. The earth and discarded skin help insulate the insect from the environment. It takes a period of up to 2 weeks for the now pupa to morph into an adult. By the time it matures it won't feed as often. The Dobsonfly could stay in the larvae stage up to 5 years depending on environmental factors. The rest of this insects lifespan is rather limited. There is about a one week period of time when the Dobsonfly is an adult. Just after mating is done they die because they no longer serve a purpose. When a female lays her eggs they are place near the site where the parents were born. As the eggs hatch the Hellgammites slide into the water, mimicking their parents lives.

Feeding Habits

Dobsonflies are nocturnal hunters. As said previously their Hellgammite stage is when they feed the most. Other aquatic insects are the prime prey of the Dobsonfly. These insects include those such as Caddisflies and Blackflies. The males have more difficulty eating during adult life because of their large mandibles. It is possible that the females feed during their adult life but it is still unclear. There is evidence of many staying on or around berry bushes, but this may just be coincidental. In captivity females are known to eat honey in small amounts. Predators are usually unlucky in their attempts to catch this creature. Although the hellgammites are often used as fish bait they are rarely ever found in fish. They are very evasive mainly due to their habitat under rocks.

The Prey! (Caddisfly Larvae)
The Prey! (Caddisfly Larvae)


Ecological Role

The Dobson Fly has a diet of mainly aquatic larvae so they are not considered pests but rather good for the environment. They eat insects such as mosquitoes and flies when they are still in their larvae stages. Therefore the Dobsonfly helps maintain the population of these pests without damaging the environment around them. Hellgammites are often used to help human kind. They can be found in shops across the world, sold for fishing bait. It is unfortunate to think that the population of the Dobsonfly and all of it's stages may soon be diminishing because of trends like this. Water pollution and excessive hunting is killing many. Some states in the U.S. even have laws against catching certain amounts of these prized King Bugs. While although not as popular as the monarch or bumblebee, the Dobsonfly is still very important in keeping the balance of life and we can only hope they won't become endangered.



A Live Dobsonfly!









New Jersey


As suggested in Geological Range, all of New Jersey is inhabited by the Eastern Dobsonfly
As suggested in Geological Range, all of New Jersey is inhabited by the Eastern Dobsonfly





The Glog!





The DobsonFly Glog



External Links


http://www.youtube.com/watch?v=9v_1_XYDC9Y




http://www.mbgnet.net/fresh/slide/dobson.htm


http://www.whatsthatbug.com/category/dobsonflies-and-fishflies/




http://entomology.ifas.ufl.edu/creatures/misc/eastern_dobsonfly.htm




http://www.fcps.edu/islandcreekes/ecology/dobsonfly.htm




http://www.themissioncalendar.org/component/content/article/76-what-is-this-thing.html
http://bugguide.net/node/view/359597