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Megaloptera

life science Maturity 5-7 Next article →

Megaloptera is an order of insects that includes alderflies, fishflies, and dobsonflies. There are approximately 300 known species within this group. The name Megaloptera comes from Ancient Greek words. The word "megas" means "large," and "pteron" means "wing." This name refers to the large and clumsy wings of these insects.

Corydalus cornutus MHNT male
Corydalus cornutus MHNT male

Many people do not encounter them often. The adults usually have very short lives. They are also crepuscular or nocturnal, meaning they are active at twilight or night. Because of this, they remain relatively unknown in much of their range.

The life cycle of a megalopteran involves a process called complete metamorphosis. This is a type of development where an insect changes through distinct stages. Among holometabolous insects, Megaloptera show the most rudimentary form of this process. This means there are fewer differences between the larvae and the adults than in other groups. The larvae are aquatic and live in fresh water. The adults also live near these same water sources. This connection keeps their entire life cycle tied to the water.

Life begins when a female lays eggs in a single mass. She may lay as many as 3,000 eggs on vegetation overhanging water. The larvae hatch and live in the water as carnivores. They use strong jaws to capture small invertebrates. Their diet includes worms, clams, crustaceans, and other insects. These larvae have large heads and elongated bodies. They also have fine tactile filaments on their abdomens. In the family Sialidae, these filaments include tracheal gills on segments 1 through 7. In the family Corydalidae, they are found on segments 1 through 8.

Corydalus cornutus MHNT male
Corydalus cornutus MHNT male

These larvae can take between one and five years to reach maturity.

When the larvae are ready, they crawl onto land to pupate. They usually find damp soil or the space under logs. The pupa stage is quite unusual because it is fully motile. This means the pupa can move around. It even has large mandibles to defend itself against predators. After this stage, the short-lived adults emerge. Some species do not eat at all during their adult lives. They may live for only a few hours or days. Other species may live for up to a few weeks.

Scientists have changed how they classify these insects over time. Megaloptera were once considered part of the order Neuroptera. This former group included lacewings and snakeflies. Now, Neuroptera refers specifically to lacewings and their relatives. Megaloptera and Neuroptera are both part of a larger group called Neuropterida. Within the holometabola, the closest living relatives to the Neuropterida clade are beetles and strepsipterans.

Corydalus cornutus MHNT male
Corydalus cornutus MHNT male

Some prehistoric taxa, like the family Corydasialidae, are also placed within Megaloptera based on fossils.

There are several distinct families and interesting physical traits to note. The two living families are Corydalidae and Sialidae. In North America, the larvae of dobsonflies are commonly called hellgrammites. Anglers often use these larvae as bait for fishing. Some adults have large compound eyes and sometimes possess ocelli, which are simple eyes. The wings are large and subequal, meaning they are nearly equal in size. However, the hindwings have a pleated region. This feature helps the insect fold its wings over its abdomen.

Some species of Megaloptera are truly massive. The Asian dobsonfly, *Acanthacorydalis fruhstorferi*, is a notable example. It can have a wingspan of up to 150 mm. This measurement makes it the largest aquatic insect in the world by wingspan.

Corydalus cornutus MHNT male
Corydalus cornutus MHNT male

In some species, such as the American dobsonfly, males have very large mandibles. These look like tusks and can appear quite formidable. However, they are relatively harmless to humans and other animals. They primarily serve to impress females during courtship. Males also use them to hold females during mating. Some males even use their mandibles to spar with each other. They attempt to flip their opponents over during these displays.

Corydalus cornutus MHNT male
Corydalus cornutus MHNT male
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