Peacock flies, in the family Tephritidae, are named for the banded, spotted, intricately patterned, and often brightly colored wings of many species. The front half of the bodies usually have noticeable, upright bristles.
Specialists confirm their identifications in this group of small to medium-sized flies by studying details of the wing venation.
Behavior helps to identify these flies: at rest, they often move their wings slowly up and down. The courtship dances and other behaviors of several species are interesting and easy to watch. Females may be identified by a pointed extension on their abdomen (see Life Cycle below).
Some examples from this family of flies include:
- The apple maggot fly (Rhagoletis pomonella), about the size of a house fly, has a black-and-white banded abdomen, a bright white spot on the back, and black-banded wings. Before Europeans introduced cultivated apples to North America, the larvae of this fly developed within the fruits of our many species of native hawthorns. It is now a pest of apples and cherries.
- The walnut husk fly (R. completa) has a light brown or amber body, iridescent, greenish eyes, a yellow spot on the back, and wings with 3 broad black bands. The larvae bore into the husks of walnuts but usually do not directly damage the nut. They may contribute to early fruit drop and smaller nutmeats. This fly is native to the Midwest but has expanded its range and is invasive in California and other western states, and it was introduced and invasive in Europe. This fly is a serious pest in California orchards of English walnut.
- The sunflower maggot (Strauzia longipennis) has a golden-amber body, multicolored eyes, and relatively long wings for this group; the wings are marbled with bold, smoky dark patterns. Larvae bore into stalks of sunflowers, but apparently do not usually damage plants seriously.
- Members of genus Eutreta (they have no common names) have rounded black wings covered with tiny white specks. There are nearly 20 species in North America north of Mexico. Their larvae form galls on the stems of plants in the daisy/sunflower family, including ragweeds, beggar’s ticks, crownbeards, and ironweeds.
- Members of genus Paracantha (again, no common names) are golden-amber with multicolored, iridescent eyes. The front of the body may look polka-dotted with brown spots. Their wings have a lacy-looking, clear outer margin; the central area is tan and decorated with numerous dark-circled clear dots, eye spots that may be blue or rust-colored, and other markings. Their larvae develop within the flowerheads of thistles (Cirsium spp.), eating the immature thistle seeds.
Similar species: There are two families of true flies that are called “fruit flies,” and this is one of them. The other family of fruit flies are the Drosophilidae; that group includes the famous Drosophila fruit flies used in genetics experiments. Members of the drosophilid fruit fly family usually have clear wings, lacking the ornate patterns of tephritids. Confusing matters more, tephritid fruit flies are sometimes called “picture-winged flies,” but that name is more commonly used for unrelated flies in the Ulidiidae family, which may also have banded or spotted wings.
Habitat and Conservation
Males and females usually court on their foodplants. Female tephritid fruit flies have a pointed, conical oviscape, which is a hard protective sheath covering the needle-like ovipositor, which they use to insert eggs into the living tissues of plants (often in unopened flowerheads). See “foods” above for the varying larval feeding ecology of various groups of tephritids. As adults, tephritids usually live for less than a week.
Paracantha Courtship Behavior
Male-female courtship, and male-male territorial competition in genus Paracantha is fun to watch. The adults walk around smoothly on the spiny stems of thistles (their food plant, into which the female will insert eggs). The flies’ mouthparts pump continuously in and out, and they repeatedly extrude a drop of clear, sugary liquid, which grows larger and larger before then draw it back in again. (With a little imagination, you might think they are chewing gum and blowing bubbles.)
Various wing movements (flicking, waving, extending, and fanning) are used for mate attraction and to ward off rivals. Two competing males may vibrate their wings, then lunge at each other and butt heads like tiny rams.
Prior to mating, the male (working his mouthparts) presents to the female a droplet of sugary liquid, which the female accepts. As she eats the gift, the male mates with her.
Some species of tephritid fruit flies are pests, including species that are destructive to olive, celery, parsnip, sunflower, and blueberry crops. The infamous Mediterranean fruit fly (or Medfly, Ceratitis capitata), native to Africa but introduced to other continents, is in this group.
On the other hand, some tephritids have been used as biological control agents for combating noxious weeds. The tephritids deposit eggs in the flowerheads of the weeds and their larvae eat the seeds before they can mature. One example is the Canada thistle stem gall fly (Urophora cardui), with groovy black wavy patterns on its wings. It was imported from Europe to help combat invasive Canada thistle (which, despite the common name, is also from Europe).
The economic importance of tephritids as pests or biological control agents has led to them being a well-studied group worldwide.
Most species in this group are not pests to human interests. Their beauty and curious behaviors make them fun to watch on hot summer days. The mating rituals and territorial displays of many species are truly interesting.
This is what bird food looks like! Tephritids are just some of the many kinds of insects that eat plants and thus convert plant nutrients into their own bodies. Birds and other predators eat the insects. Even bird species famous for eating seeds require insects during breeding season, because they need additional protein as they raise young.
Tephritid fruit flies, with their ornate wing patterns, colorful bodies, wing-waving motions, and other behaviors, may mimic jumping spiders and/or wasps, and this mimicry apparently serves to protect them from some predators. Indeed, predation by jumping spiders — a major enemy of these flies — may be why tephritids developed their special wing markings. In some species, the wing marks resemble the legs of jumping spiders. The wing movements, combined with the color patterns, replicate the semaphore-like warning motions of jumping spiders. Tephretids in genus Rhagoletis (including the apple maggot fly) are some of the flies that mimic jumping spiders.