Assassin or robber, this fly is on the most wanted list A robber fly, Microstylum morosu, with the facial bristles, or mytax (“moustache” in Greek), visible. Bottom-left: Up-close view of tiny assassin (or "robber") fly, genus Holcocephela, that eats tiny prey such as mites. (Eric Isley via iNaturalist, CC-BY-NC/Smithsonian image by Torsten Dikow)
Assassin or robber, this fly is on the most wanted list
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What animal has been witnessed snatching a bee from mid-air, stabbing it with a sharp tool and sucking out its insides? An assassin fly is the culprit.
 
Also known as robber flies, they stand out in their penchant for preying on other insects. While you may not know it, you've probably crossed paths with one of these predatory flies. There are more than 7,500 species of them distributed around the globe.
 
All flies are suction feeders. But, many of them, including the common house flies we see buzzing around our lunch, do not kill prey. If you stare at a house fly (Musca domestica) feeding before you swat it away, you can see it swabbing at your food with its long mouthparts. This "proboscis" is part paintbrush, part straw. It is specialized to sponge digestive enzymes onto food, then ingest the liquid food, whether it's a piece of your cantaloupe or some spilled sugar.
 
Assassin flies, members of the family Asilidae, have evolved a predatory twist on this feeding behavior with a proboscis that is part injection needle. The sharp proboscis is used to pierce the hard bodies of other insects and inject paralyzing venom. Digestive enzymes accompany the venom and turn the insides of their prey to liquid. Then, the typical sucking action is used to ingest the liquefied guts.
 
While assassin flies can be tiny, their ambitious feeding mode allows them to consume insects larger than themselves.
 
Assassin flies prey on a variety of insects, including stinging bees and wasps. The bristles on their face and body may shield them from the dangers imposed by their prey. Like other flies, assassin flies benefit from oversized, compound eyes. These help them detect fine movements of prey. Their hindwings are converted into little gyroscopic devices. These stabilize them during flight, conferring maneuverability.
 
Entomologist Torsten Dikow has described 68 new species of assassin flies and closely related flies. He continues to grow the collection at the Smithsonian National Museum of Natural History. Learn more about his work with these predators in the "Smithsonian Science How" webcast on Thursday, April 6, 2017. During Assassin Flies: Predators of the Insect World (airs at 11 a.m. and 2 p.m. EDT on the Q?rius website), Torsten will take you on a tour of his fly lab while answering your questions live. You can also get teaching resources to use with the webcast.

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CRITICAL THINKING QUESTION
Why do many insects have hard bodies?
Write your answers in the comments section below


COMMENTS (17)
  • andresb-
    3/29/2017 - 08:35 a.m.

    insects have a hard exoskeleton to protect all of their organs. and to keep them safe from potential predators.

  • temmy-dav
    3/29/2017 - 10:17 p.m.

    In response to this article, I believe that these flys are helpful to the planet. One reason i sat this is that like spiders they kill insects that would overpopulate if not eaten. Another reason is that they are not harmful to humans. A third reason is that they would be very interesting specimen to study. Even though I think this some others may think they are annoying and not want them around.

  • crowan-dav
    3/30/2017 - 06:27 p.m.

    The assassin fly or robber fly has a snatcher or stinger that can pierce through another insect's body to eat. This fly even kills bees. It says in the passage, "While you may not know it, you've probably crossed paths with one of these predatory flies," which shows they are pretty common, "their ambitious feeding mode allows them to consume insects larger than themselves." The passage doesn't say if they can hurt humans but I would imagine they could since they can rip through insects "shell".

  • eharlan-dav
    3/30/2017 - 07:00 p.m.

    In response to "Assassin or robber, this fly is on the most wanted list" I agree that this fly should be studied. One reason that I think it should be studied is that it would be an interesting topic to look and see how it adapted to live and hunt for food like it does. Another reason is we could figure out how to genetically modify other animals with this same ability and adaptations on its flying methods and hunting methods as it talks about its special flying habits "Their hindwings are converted into little gyroscopic devices. These stabilize them during flight, conferring maneuverability."

  • brycew-orv
    4/01/2017 - 02:22 p.m.

    Why is a bug on the most wanted list that makes no sense

  • madelync-
    4/03/2017 - 08:38 a.m.

    Insects have hard bodies because it shields them from being imposed by their prey. Their hard body helps them from not getting major injuries.

  • saraip-
    4/03/2017 - 08:46 a.m.

    I really think this insect is scary because what happens this Assassin fly come in contact with a human. like can it kill humans too? Are we safe?

  • kimberlyc-
    4/05/2017 - 08:37 a.m.

    Insects have hard bodies to protect them from their predators,sometimes it can be helpful but other times it doesn't work

  • NevaehL-wik
    4/19/2017 - 10:37 a.m.

    They have hard bodies because of their exoskeleton.

  • nylao-orv
    4/19/2017 - 11:54 a.m.

    Assassin flies prey on a variety of insects, including stinging bees and wasps. The bristles on their face and body may shield them from the dangers imposed by their prey.

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