A Little Bit More
Flies don’t get much respect! But if you can be objective about them for a moment, you’ll soon realize that they really are incredible animals. One of the most interesting aspects of true flies (Diptera), to me, are their modified second wings called halteres. Halteres are not only important to flies, they’re essential; flies can’t fly without them! These barbell-like structures located just behind the wings, can be thought of as a balancing and guidance system for flies. It’s interesting to note that the French word for barbells is “halteres” and it’s easy to see why once you see them.
dead Crane Fly
The halteres vibrate as the animal navigates and allow a fly to monitor changes in direction and attitude . Since so many flies are quite small, if you want to get a good look at the halteres, the larger species of crane flies are excellent subjects for seeing these structures with the naked eye.
During the summer months, most of us have had a crane fly blunder into our homes and crash against the window. If you tried to pick it up or capture it with a net, you soon learned that their long, skinny legs are extremely delicate and break off with the least bit of pressure. In Great Britain, these flies are called “Daddy-Longlegs” and it’s no wonder why.
There are well over 15,000 species of crane flies worldwide and they’re typically found in wet habitats. Immature crane flies, often called “leather jackets”, are often aquatic or semiaquatic although some are terrestrial. For the most part, the larvae feed on various kinds of vegetable materials – there are few predaceous species - but as adults, most do not feed at all and therefore pose no threat to you. Crane fly numbers often make up a large and important part of aquatic habitats and are an important link in the food chain where they live.
Activities
Science - Living Barbells
Objectives: Examine the halteres on a variety of flies
Materials: Flyswatter, hand lens or magnifying glass, jars with lids
Obtaining animal subjects for close inspection can be difficult in many instances, but this activity should be quite easy for everyone. In the “Little Bit More” part of the unit, we pointed out the fact that the French word for barbells, is “halteres” - this may be an easier way for your students to remember what they are. So whether you call them halteres (hall-TEERS), or barbells, these structures are found on all adult flies. This activity should make it clearer exactly what a haltere looks like and we hope will also firmly establish one of a fly’s key anatomical characteristics in their minds.
Have your students find a bunch of flies – all kinds, big and little, alive or dead – that can be brought in for examination. You can find flies in the house, garage, in the yard, just about everywhere you look. Any flies that are captured that are not dead can be placed in the freezer and they’ll meet a quick and painless death. Do keep in mind that since dried body parts from long-dead insects can and do break off when handled, be sure this doesn’t confuse your students. It’s very important that adults model a respectful attitude toward animals so you may not even want to kill any insects for this exercise. If you do, make sure all understand that this is a way to learn more about flies, and that they’re being killed in a humane way (the freezer method) so they will feel no pain. Although humans usually don’t afford much empathy toward insects, it is important that all creatures be treated in a “respectful” manner so please be sure to model humane treatment of your subjects.
Once you’ve accumulated an assortment of different flies, use a hand lens or magnifying glass so you can inspect the halteres. You may find that some of the collected “flies” do not have halteres, and this will be a good clue that they really aren’t flies at all – look again. Remember, flies have only one pair of functional wings and one pair of halteres. If you have access to a dissecting scope, you’ll have an especially good view of these structures. You can pass the insects around the room so all can see or better yet, set up stations and have the students come to the different stations to inspect their insects.
Incidentally, the reason we know that flies can’t fly without their halteres is that researchers captured some live flies and removed their halteres as an experiment and found that each fly was rendered totally incapable of flight. Not a very humane experiment to be sure, but it did provide information on the importance of these tiny structures.
One Step Further
1. See if your students can determine where the halteres are attached – head, thorax, or abdomen
2. Ask your students if the halteres on different flies are different in shape, proportion, or color
3. Ask your students if they think immature flies (maggots) would have halteres. If so, why; if not, why not?
Key Concepts
Structures and Functions, Identification, Adaptations and Diversity
Questions
Do you have a question for a naturalist? Go ahead and ask!
It's easy -- just fill out this form, submit your question and you'll receive an answer shortly.
Posted by Ralph Meacham on August 24, 2006 at 08:00 PM
Q: Giant Red Ant about 1 inch long, banded, and fury. I think they may be called cow ants in N.C.
A: You've seen a kind of wasp called a Velvet Ant or Cow Killer. These wasps parasitize other wasps and bees and can sting if handled. Try googling this animal to be sure my identification is correct. Thanks for sharing.
Posted by jennifer golla on August 02, 2006 at 08:41 PM
Q: My front garden is full of carpenter/bumble bee sized mosquitos. Today I saw one land on a bumble bee pick it up and suck the life out of it. I am totally serious my husband was there with me and he tried taking a picture of it but it flew at him. we live in douglassville pa and we do get standing water on the creek next to our lot. It didn't really look like a crane fly it was fatter and had mosquito like sucking mouth parts. this thing sucked that bee quarter sized bee dry and the bee couldn't fight back it submitted instantly. What is this thing? can it hurt us?it wasn't floppy like a crane fly, i hope you can help me.
A: Oh my, I just did a unit on this kind of insect! You were lucky and got to see an interesting animal called a robber fly in action. There are quite a few robber flies and they do indeed often capture bees and wasps, inject a special saliva that stuns their prey and then suck up the predigested inner tissue. You needn't worry as these flies won't bother you at all. Check out our Oct 30 week's unit and you'll get to see a picture of two of these inteesting creatures along with info on them. Thanks so much for writing.
Posted by Sam ******* on June 19, 2006 at 03:50 AM
Q: how do you get rid of them!!!!!
A: Easy, you simply darken the room you're in, (cover your computer screen) put a light on in another room and when the crane fly moves into the lit area, close the door. Crane flies are totally harmless although I suppose no one wants them bouncing around their computer screen. Hope this does the trick for you.