Large dobsonfly looks like something from horror movie

  • The dobsonfly has a cylindrical body and feathery antennae. A female is shown here.

    The dobsonfly has a cylindrical body and feathery antennae. A female is shown here. Courtesy of Karen Lund

 
By Mark Spreyer
Stillman Nature Center
Updated 6/24/2019 6:20 AM

Old black-and-white monster movies often featured giant spiders or ants rampaging through the countryside. Think of this story as a reality version of "Creature from the Black Lagoon."

Attack of the megaloptera

                                                                                                                                                                                                                       
 

Megaloptera; doesn't that sound like something Godzilla should be fighting? Actually, megaloptera is the insect order that includes fishflies, alderflies, and this column's insect horror star, the dobsonfly. To be specific, I am writing about the eastern dobsonfly (Corydalus cornutos).

How did this insect come to be called a dobsonfly? Nobody knows for sure.

However, this is one big insect. The wings folded measure two inches in length. When opened, the wings are five inches across. It is not surprising to learn that megaloptera means large wings.

Dobsonflies have gray, translucent wings that are lined with dark veins. At rest, the wings are curved over the top and side of the dobsonfly. Should you touch a dobsonfly, the wings are soft, almost feathery.

Now, if you've found a male dobsonfly, which sports a pair of sickle-shaped mandibles that are over an inch long, you're thinking, "Touch that? Are you crazy?"

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Although it may be hard for some to believe, I'm not crazy. The male's lengthy ornamental mandibles are used in breeding and defense. Rest assured, the males are harmless, but they will get your attention.

It's the female dobsonfly you should be careful with. Her much shorter mandibles are quite effective at inflicting a painful bite. What do they eat with these mandibles? Nothing. Dobsonflies do not eat as adults. They leave the eating to the larvae.

To hellgrammite and back

Believe it or not, young dobsonflies are called hellgrammites. Isn't that a great name for a monster? It is also an appropriate name for the somewhat creepy looking larvae.

The three-inch long larvae look like large underwater centipedes. They are usually dark brown to black in color. In addition to six legs on the thorax, the abdomen sports eight pairs of pointed appendages. These abdominal appendages appear to have hairy armpits. These tufts are filamentous gills that allow the critter to breathe underwater.

                                                                                                                                                                                                                       
 

Generally, hellgrammites prefer a stream's or river's moving waters. However, some live in ponds and lakes, which accounts for the adult dobsonflies we find here at Stillman Nature Center.

We rarely catch hellgrammites during our pond study classes since they are active at night. Unlike the adults, the larvae put their jaws to good use.

Hellgrammites eat everything from tadpoles and small fish to other aquatic larvae. They hunt their prey along the bottom muck where they'll live for two to three years.

Not only are hellgrammites good at eating, they are good for eating. Anglers love to use them as live bait to catch popular game fish such as trout and bass.

What's in a name?

Before wrapping up, let's look at this larva's intriguing name. The first syllable is self-explanatory, but the last two syllables are particularly telling. Going back to the Old English of the 15th century, we find the word grima, which refers to a "bogey or haunting spirit." So what we have here is a specter from hell. What a perfect title for a summer monster flick!

• Mark Spreyer is executive director of the Stillman Nature Center in Barrington. Email him at stillnc@wildblue.net.

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