Arthropods 11

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Southern California Arthropods #11: Flies (Order Diptera)
© W.P. Armstrong 17 November 2009
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Robber Flies (Order Diptera: Family Asilidae)
Powerful, Predacaeous Flies That Capture Bees

Two species of robber flies: The right fly is called the bumble bee robber fly.

Bumble bee robber fly clinging to a fence while it feeds on a honey bee.

Tachinid Flies (Order Diptera: Family Tachinidae)

Large, Hairy Flies That Visit Fall-Blooming Flowers

A large tachinid fly in Zion National Park (possibly Paradejeania rutiliodes). This species frequently visits rabbitbrush (Chrysothamnus) during the fall months. Tachinid larvae commonly parasitize other insects. In fact, tachinids are second only to parasitic wasps in controlling insect populations.

A large tachinid fly in Zion National Park gently sitting on the author's index finger. This species frequently visits flowering rabbitbrush (Chrysothamnus) during the fall months. Tachinid larvae commonly parasitize other insects. In fact, tachinids are second only to parasitic wasps in controlling insect populations.

Another handsome species of tachinid fly.

Bot Flies (Oestridae and Cuterebridae)

Bot flies are host-specific flies that infect rodents, rabbits, livestock, and humans. Adult bot flies of the genus Cuterebra are large and bee-like and do not feed or bite. Females deposit eggs around the openings of small mammal nests, burrows, and along runways. Host animals become infested as they pass through contaminated areas. The eggs hatch in response to the heat from a nearby host. The larva enters the host's body through the mouth or nostrils, or through mucous membranes. After penetration the larva migrates to various species-specific subcutaneous sites. The full-grown larva of wood rat and rabbit bot flies is a large, spiny grub called a "bot." The mature larva lies just beneath the skin, often at the neck or shoulder. It forms a swollen nodule (warble) with a hole (warble pore) in the center through which it breathes.

When the larva is ready to pupate, it emerges through the warble pore and drops to the ground where it forms a protective puparium (pupal case). The adult bot fly emerges from the puparium and superficially resembles a large, dark bee with a white, fuzzy underside. It lacks mouthparts and does not feed. Two species of Cuterebra in southern California include C. tenebrosa that parasitizes wood rats (Neotoma fuscipes) and C. lepivora that parasitizes cottontail rabbits (Sylvilagus audubonii).

Two views of the puparium of a bot fly (Cuterebra sp.). This may be the rabbit bot fly because of nearby cottontail rabbits; however, there are also wood rat nests within 50 meters of where the larva was collected.

Adult bot fly (Cuterebra sp.) after emerging from its puparium. The end of the puparium (top center) was broken off as the larva pushed out.

Adult bot fly (Cuterebra sp.) after emerging from its puparium. The underside of adult fly is covered with fuzzy white hairs. It has no mouthparts and does not feed.

Close-up view of the face of an adult bot fly (Cuterebra sp.).

A Bot Fly That Emerged From A Human

Larva of a human bot fly that emerged from an opening in the skin.
[Photograph by Christopher S. Boykin. Adult fly courtesy of USDA.]

The human bot fly (Dermatobia hominis) belongs to the insect order Diptera, family Cuterebridae. The adult is a stout-bodied, hairy fly native to Central and South America. In fact, the above larval hitchhiker was "picked up" in Costa Rica. The egg-laden adult female fly temporarily captures a mosquito and attaches her eggs to its body. This encounter presumably occurs during the hours of dusk or later. When the mosquito lands on the warm body of a human for its blood meal, the bot fly eggs hatch and one or more pear-shaped larvae (maggots) fall to the skin surface. The larva bores into the skin and leaves a small "breathing pore."

 		When it has penetrated the epidermal and dermal layers of the skin, it is firmly held in place by anal hooks and rows of barbs on its body (see image to the left). It takes about five to ten weeks for the larva to complete its development. During this time it feeds on blood tissue within its subcutaneous burrow.
When mature, it emerges from the breathing pore and drops to the ground where it pupates and gradually transforms into a winged adult through metamorphosis. The adult has nonfunctional mouthparts and does not feed. Its primary purpose is to mate and perpetuate the species by capturing another mosquito. Insects truly have some of the most complex and remarkable life cycles of all the creatures on earth.

Moth Flies (Order Diptera: Family Psychodidae)
Bathroom Fly (Clogmia albipunctata): A Tiny Fly In Your Shower
The moth fly family (Psychodidae) includes some minute species of flies. They are called moth flies because of the conspicuous hairs on their wings that are easily shed like the scales of moth wings. In addition, their bristly, many-segmented antennae superficially resemble a moth. One species called the bathroom fly (Clogmia albipunctata has a wingspan of only 3.0 mm (1/8 of an inch), about the size of a tiny gnat. It is also known in the literature as Telmetoscopus albipunctatus). Although seldom seen by the casual observer, this fly is a common synanthropic (living with humans) species with a widespread distribution throughout tropical and subtropical regions of the world. Indoors it is often found on the walls of bathrooms, showers and washrooms. According to Dr. Charles L. Hogue (1993), the brown, worm-like larva develops in organic muck that accumulates outdoors in shallow pools and tree holes. It also develops indoors in sink traps, drains and dead-flow areas of the household plumbing. In fact, it has also been called the "drain fly." This interesting species has also been found in sewers and near wastewater treatment plants.

A bathroom Fly (Clogmia albipunctata). The wing span is only 3.0 mm (1/8 in.)

The following two references describe cases of myiasis (infestation by fly maggots) in humans caused by the larvae of Clogmia albipunctata:

Mohammed, N., and K.G.V. Smith. 1976. "Nasopharyngeal Myiasis Caused by the Larvae of Clogmia (= Telmetoscopus) albipunctatus Williston (Psychodidae, Diptera)." Transactions of the Royal Society of Tropical Medicine and Hygiene Vol. 70 (1): 91.

Smith, K.G.V. 1979. "Intestinal Myiasis in Man Caused by the Larvae of Clogmia (= Telmetoscopus) albipunctatus Williston (Psychodidae, Diptera)." Transactions of the Royal Society of Tropical Medicine and Hygiene Vol. 73 (3): 349-350.

Horse Flies (Order Diptera: Family Tabanidae)

Horse fly (Tabanus punctifer), a large biting fly in the family Tabanidae.

Crane Flies (Order Diptera: Family Tipulidae)

The Most Misidentified Flies In Southern California

Crane flies are often mistaken for giant mosquitoes. Although crane flies and mosquitoes both belong to the insect order Diptera (true flies), they actually belong to entirely different families. They are often called "mosquito hawks," although they do not prey on mosquitoes. The soft, fragile mouthparts of crane flies make them incapable of biting. In addition, their long, clumsy legs are very fragile and break off easily. Crane flies are attracted to lights and often sit on windowsills, walls and doorways. They commonly enter houses during the evening as you walk through your doorway.

The common crane fly (Tipula planicornis) compared with a U.S. penny.

Crane flies develop from large, worm-like larvae called "leather jackets" because of the brown color of their skin. The larvae of terrestrial species live in moist soil or leaf mold where they feed on decaying wood and vegetation, fungi, mosses, and the roots of herbaceous plants. In some species the larvae are completely aquatic and live in ponds and streams. When fully grown the larvae metamorphose into pupae. They are very abundant in weedy fields in spring, especially during years with high rainful and bountiful annual grasses and herbs. Often swarms of adults appear after mowing. Like many other insects, the adults are relatively short-lived and their main purpose is to mate and perpetuate the species.

The brown larva of a crane fly.

Size relationships used in Wayne's Word articles.

Beware Of False Pennies Used In Size Relationships

Mosquito (Order Diptera: Family Culicidae)

Well-Known Flies In Southern California

The mosquito family is readily identified, particularly if a female mosquito is sucking blood out of your arm through her long proboscis. Only the female "bites" (sucks blood), the male feeds on nectar and fruit juices or not at all. She needs the proteins from her blood meal to develop eggs. She pierces the skin with her long probscis, tipped with minute cutting organs. An anticoagulant is secreted into the wound to keep the blood flowing. Depending on the species, mosquitoes also bite other infected host animals, such as birds horses and rodents, and are the vector of a number of dreaded diseases, including malaria, encephalitis, denge fever, yellow fever and West Nile virus.

Female house mosquito (probably the genus Culex). Males have a bushy antenna.

Close-up view of head of female mosquito.

Bee Flies (Order Diptera: Family Bombyliidae)

This little hump-backed bee fly belongs to genus Geron. It is roughly the size of a mosquito with a long, rigid proboscis and pair of short antennae typical of bee flies (Bombyliidae). Its flight is erratic with short up and down movements. It was identified by Dr. Neal Evenhuis of the Bishop Museum, Hawaii.

A species of bee fly in the very large family Bombyliidae. It belongs to the genus Villa. This interesting fly is about the size of a honey bee with a fuzzy body similar to many bees.
Bee flies have a long, rigid proboscis for sipping nectar from flowers. On warm, sunny days bee flies are often seen hovering over flowers or resting on the ground. While hovering, they probe flowers for nectar with their long proboscis, like miniature hummingbirds. They are fast-moving flyers and probably evade predators lurking in the flowers (ambush bugs and crab spiders) by not actually landing on the flower. In the following image, pupal cases can be seen in or around small holes in the ground dug by solitary bees (family Andrenidae). The larvae of bee flies are parasitic on the larvae of solitary bees within their burrows. The bee fly in the following images was identified as Bombylius montanus by Dr. Neal Evenhuis of the Bishop Museum, Hawaii. They are typically parasitic on bees of the genus Anthophora (Apidae). According to Dr. Evenhuis, this is a relatively rare species also known from Walker Pass in the southern Sierra Nevada.

Bee fly pupal cases within or near the burrows of solitary bees.

This furry fly has a long, rigid proboscis that it uses for sipping nectar from flowers.

  See Bee Flies & Their Host--A Solitary Burrowing Bee  

Syrphid Flies (Order Diptera: Family Syrphidae)

Alpine daisy and syrphid fly photographed on Logan Pass, Glacier National Park.

Cactus Fly (Copestylum mexicana). The larva feeds on rotting cacti.

The following link shows a syrphid fly hovering in midair. It was taken through LCD
screen at arm's length on a hand-held Sony T-9 at a distance of 4 inches (10 cm).
This fast-moving fly is difficult to get close to while it is in flight. Very difficult photo.
     Syrphid Fly Hovering in Midair  

References:

  1. Evans, A.V. 2007. Field Guide to Insects and Spiders of North America. Sterling Publishing Co., Inc. New York, New York.

  2. Hogue, C.L. 1993. Insects of the Los Angeles Basin. Natural History Museum of Los Angeles County.

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