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
Lexile

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, and while you may not know it, you've probably crossed paths with one of these predatory flies, as 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 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, which help them detect fine movements of prey. Their hindwings are converted into little gyroscopic devices that stabilize them during flight, conferring maneuverability.
 
Entomologist Torsten Dikow has described 68 new species of assassin flies and closely related flies, and 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 (23)
  • mikeb-pay
    3/29/2017 - 08:22 a.m.

    An assassin fly name the culprit also know as the robber fly. This fly can kill a bee in mid air. It was going to kill the bee by stabbing it and sucking it inside out. that is why they call it the robber fly. it move so fast that there enemy don't see them in time.

  • keasiak-bur
    3/29/2017 - 07:00 p.m.

    Most insects have hard bodies to protect other parts of their bodies from harm and or danger. I think that insects have hard bodies so that these assassin flies and other predators have a harder time hurting or killing them.

  • brendanw-kut
    3/30/2017 - 03:02 p.m.

    Evolution has always fascinated me. When you think you know everything about an animal, you discover something like this. This makes you really question rather you know so much about the world. If you think about it, this could be a very minor change compared to some other. In truth, we will never know everything about our modern world but we can still discover.

  • princessf-bur
    3/30/2017 - 06:48 p.m.

    Most insects have hard bodies because their are certain parts insects want to protect from their predators. I personally thought that the reason why insects had hard bodies is because they had bones.

  • makilahs-pay
    3/30/2017 - 10:42 p.m.

    Many insects have hard bodies to help shield them from danger they impose by their prey.Insects do not have bones like you and I, but instead they have a hard outer covering known as "exoskeleton".

  • zakrym-ste
    3/31/2017 - 01:18 p.m.

    They have hard bodies because it is a protection against their preys defense mechanism. It is a way of protecting them.

  • nathanm14-ste
    3/31/2017 - 01:29 p.m.

    Insects have hard bodies because they have no bones, rather an exoskeleton to protect their mushy insides. But apparently it cannot protect them from the assassin fly's sucker thing.

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

    Many insects have hard bodies to protect their insides since they don't have bones.

  • jahir-orv
    4/04/2017 - 12:03 a.m.

    Well they're are not called bodies they are either called abdomens or if they are harder they are called exoskeletons. now the reason I conjecture insects to have hard bodies is because of evolution. Insects in some way, were being effected by something so they evolved or adapted into having exoskeletons.

  • keithj-pay
    4/04/2017 - 11:14 a.m.

    Robber flies take a bite out of anything, they will dine on insects. It is good that they eat harmful insects that we don't wanna deal with. The robber flies are considered to play a role in maintaining our gardens. Assassin flies detect movements of prey, they are fierce and attack on insects such as bees or wasps. Both flies have aspects of a killer and share similar strategy.

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