Dance Fly
Pages
Several kinds of morphological traits are discussed here:
Mating-related traits:
(password required)
Other structures: (coming soon)
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| the Dance Fly Pages |
Morphology |
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| About Dance Flies | The morphology
of dance flies is diverse, reflecting their diverse behavior and
ecology. Some of the most fascinating and unusual traits are
probably the result of sexual selection,
and are involved in attracting mates or in the act of mating itself.
Because of this, males and females of the same species may look
very different. In
most insects only the male shows exaggerated sexual traits, but in
dance
flies it is usually the female that has more conspicuous ornaments and
coloration to attract the male. This is probably because dance
fly males put more effort into wooing a mate, by catching and
presenting insect prey (see Behavior), and have consequently become
more choosy. In male dance flies (as in many other insects), the
sexual organs (genitalia) often have complex, species-specific
structures. In some male dance flies, the aedeagus (male organ) may be very long, sometimes even longer than the rest of the body! |
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Several kinds of morphological traits are discussed here:
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| About this Project |
Mating-related traits:
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| Workgroup (password required) |
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Other structures: (coming soon) |
| Female ornaments: Female ornaments in dance flies are of four main types, illustrated below. All of these presumably function to attract the attention of a male, or to appear larger (an indication of egg number or maturity). Each type is found in several, presumably unrelated groups, and probably evolved multiple times. |
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| 1) broad, pennate scales on the legs | ||
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| Empis anthophila (USA) | Rhamphomyia pectinata (USA) Rhamphomyia pennata (Germany) | Rhamphomyia longicauda (USA) |
| 2) darkened, patterned, or expanded wings | ||
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| Macrostomus smithi (Guyana) | Empis borealis (Germany) Rhamphomyia clavator (USA) | Hilara melanogyne (Japan) |
| 3) inflatable sacs on the abdomen | ||
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| Rhamphomyia longicauda (USA) (D.H. Funk, Nature Mag.) |
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| 4) reflective coloration | ||
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| Hilarempis argyrozona (Chile) Rhamphomyia (Megacyttarus) sp. (Japan) | ||
| Male genitalia: The structure of the male genitalia is often used to tell species apart in insects, because of its complex, species-specific structure. Some dance flies have taken this to an extreme, and the exposed aedeagus (male organ) may be very long and/or curvy. The reason for this is not yet clear, but a long aedeagus may reflect strong sperm competition: because females mate with several different males, each male needs to place his sperm inside the female ducts as close as possible to the ovaries to maximize his number of offspring. A curvy aedeagus may have evolved because it is preferred by females, or possibly because it delays premature disengagement of the female during mating; however, this has not yet been studied in dance flies. |
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| Rhamphomyia idonea (USA) | Empis spiralis (Cyprus) Rhamphomyia clavator (USA) | Empis splendidella (Japan) |
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| In a few species of dance flies, part or all of the genitalia are grossly enlarged. In some species this may simply serve to enclose and protect an elongate aedeagus, but it may instead serve as ornament to attract female attention. | ||
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| Hilarempis gubernator (Chile) | Hilara urophora (New Zealand) | Rhamphomyia longicauda (USA) |
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| R. deformicauda (closeup) | Rhamphomyia deformicauda (Japan) Rhamphomyia nigrita (Greenland) | |
 E. poplitea (closeup) |
Other male structures: Male ornaments and other male-specific structures are much less common in dance flies. The major exception is the expanded male front tarsi of many species of Hilara and several related genera, which contain a silk gland. A few other empidine species have unusual modifications of the legs or abdomen, possibly for clasping the female or stimulating her during mating. One of the most unusual examples is that of Rhamphomyia scaurissima and several related species, in which the middle tarsi are expanded such that from profile it appears as if the fly is carrying a small insect as prey. |
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| Empis poplitea (USA) | Hilara maura (England) Rhamphomyia scaurissima (USA) | R. scaurissima (closeup) |