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A site for parents, teachers and bugdorks.

Sexual Dimorphism: how males and females look different

Dobsonfly Sexual Dimorphism TBC

I promised you dobsonflies! I think these megalopterans are one of the best examples of sexual dimorphism, where males and females have different body forms. These large insects start their lives as larvae in streams. Back east we call them hellgrammites or ‘toe-biters’ (though some people reserve that name for giant water bugs.)  Once they pupate the adults have long wings and awkward fliers. But they are pretty spectacular looking insects.

In dobsonflies, the adult males have elongate mandibles. They use them to battle each other for mating rights like the stag beetles in last week’s post. 

Females will choose the males with the longest mandibles that can still fly well. No point passing on genes that may inhibit movement when escaping from predators or finding new territory!

female dobsonfly celestron

Those long mandibles on the male can be intimidating for people. But they are so long they lack leverage to give a proper bite. It’s the females that can inflict a painful bite. Shorter mandibles = more leverage. I have been nipped by a female and it was…educational, if unpleasant.

dobsonfly wing celestron

While I had the dobsonflies out I wanted to put their wings under the scope. They are very intricately veined and pigmented. I like the white dots. However, they are difficult to photograph well because the wings have lots of peaks and valleys, highs and lows. This makes the focus stacking difficult.

I think I will bring these specimens down to the National Science Teacher’s Association annual conference workshops I’ll be teaching at the end of March. Will you be there? What other insects display sexual dimorphism?




Join the discussion

  1. CritterChick

    I think the most fanstistical displays of sexual dimorphism occurs within species of the bag worm moth family. They are neat critters all around, when they’re young caterpillars they spin their cocoon, then carry it around like a snail shell, they poke their head and legs out the front to move and eat, then they shove frass out the hole in the back. When they’re ready to pupate, they close up the end holes. Evergreen bag worm moth males go through a complete metamorphosis inside their cocoon, emerging in the spring with wings, and a very furry black body. Adult females look are pale yellow, and maggot-like, with no wings or fur. They look COMPLETELY different! After the adult females mate, they don’t lay eggs, they just seal up their cocoon for the winter, and the babies will emerge from the mother’s carcass in spring. So if you find one of their sealed cocoons, you’ll either have one adult male in it, or a ton of babies. I’ve got a cocoon that I’ve been waiting on for a few months now, only a month or so longer till I know what I’ve got. The anticipation is killing me, lol. When it hatches, I’ll take a few photos, then release him/them on the tree I collected them from (I try to be a responsible critter enthusiast).

  2. Ted Welch

    Dear Bug Chicks:
    I am a retired elementary school teacher and remodeling contractor with a lifelong affinity for bugs. I currently work as a volunteer with the Fairfax Park Authority as a Virginia Master Naturalist. A group of us regularly monitor local streams in the County watersheds for the diversity of benthic macroinvertebrates, often times including school children in the process. I have discovered that children and adults find low power magnification of the specimens they find to be extremely useful as a learning aid – especially if it can be done streamside while their feet are still wet. What I am now realizing is that many magnified images can be more meaningful if there is way to show comparative size with a familiar object, eg. a penny or a dime. Have you considered including a similar familiar object in your online photomicrographs to give scale to the image? I have experimented with 1/4″ graph paper backgrounds and petri dishes etched with cm. and mm. grids. But most people really seem to relate best to common objects for getting a sense of scale.

  3. Patti

    Hello to you both! I love your commercial, so here I am! I love bugs. I get dobsonflies all the time here in CT, but they don’t seem to last too long. I have shared my love of bugs with my granddaughter and grandson. She, especially is intrigued. Glad to be part of you site.

  4. Shelley Boren

    I think you’re so cool. Bugs fascinate me. I’m 60 years old & I’m always looking for bugs where ever I go. Hope I never lose my curiosity. Keep up your good work.

  5. Linda Walkup

    Praying Mantis females are much larger and have a fatter abdomen (for holding eggs). The most spectacular insect dimorphism I have seen are bagworms (type of moth I believe). The females stick whatever hard materials are available to a protective case around their abdomens and drag it around as larvae. They develop in this and never fly. The males pupate and become moths, and come to the ground bound females. My daughter recently kept a similar species where only the males flew. Have to borrow the photos. We are both into bugs, and have coached/competed in Entomology for Science Olympiad.

  6. thebugchicks

    Shelley, you are lovely. Thank you for writing! We love the work we do and hope to continue it for many years. We are currently in process of pitching a TV show so cross your fingers. We need some positive science programming!

  7. thebugchicks

    This is a great idea, actually. It can be hard for people to really get a grasp on how big (or small) things are when I take pics with the scopes. I will think about the best way to make that happen. Thank you!

  8. thebugchicks

    So glad to have you here Patti. It’s been crazy for us since the commercial aired. And we are working hard to get a television show that promotes women in science that is fun and factual. Love that your granddaughter is into bugs!

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