Are flies horrible pests or do they have value to the environment?
You can answer yes to both, and you’d be correct.
Some flies certainly are a nuisance, some can spread disease, and flies roll around in yuck, muck and poop – oh, wait, that’s a good thing. Rephrased, flies help break down organic material which helps keep the environment cleaned up. Flies also pollinate plants, another positive.
I was happy that a variety of flies showed up in our yard and on the moth sheet during the 17 days and nights of the recent Texas Parks & Wildlife Department’s annual Texas Pollinator BioBlitz 2024. I entered a dozen fly species observations into the BioBlitz.
Robber Flies
Robber flies are my favorites. I like their name. It conjures up all sorts of interesting scenarios. I like their looks, too. As bugs go, they’re rather dapper, in a rugged sort of way, kinda like the Marlboro Man, in commercials long banned from television advertising. But I digress.
You want to have robber flies in your yard and garden. They won’t steal the family silver. The name robber reflects their predatory habits. They are also called assassin flies because of their ruthless proficiency in their predatory skills.
They are hairy-bodied, have a long, narrow, tapering abdomen containing segments that may be banded, patterned or contrasting in color, according to Texas A&M AgriLife Extension online “Field Guide to Common Texas Insects.”
Some robber flies are stout, some are fat-bodied bumblebee mimics, some are tiny, and others may be two to three inches in length.
Wikipedia describes robber flies as a powerful built, bristly fly with a short, stout proboscis enclosing the sharp, sucking hypopharynx (a tongue-like structure in insects with chewing mouthparts). The stiff facial bristles are called the mystax, thought to protect the fly’s head and face when challenged with an aggressive opponent. Read their long list of prey below the photos and that statement will come to life.
Photos below are of a Northeastern Hammertail robber fly, Efferia aestuansrairie, at left and Prairie robber flies, Diogmites angustipennis, also called hanging thieves, at center and right. (Photos by Anita Westervelt)
Robber flies attack a very wide range of prey, including other flies, beetles, butterflies and moths, various bees, ants, dragonflies and damselflies, Ichneumon wasps, leafhoppers, grasshoppers and some spiders. Stink bugs, bumblebees, biting flies, mosquitoes, Japanese beetles, wasps, yellow jackets and hornets are attacked by robber flies; this might make some of you cry: even hummingbirds are prey to robber flies.
A robber fly stabs its catch with its short, strong proboscis and injects its victim with saliva containing neurotoxic and proteolytic enzymes which paralyze the victim and quickly digests its insides. The robber fly is then able to suck the liquefied material through the proboscis, according to Wikipedia.org.
But, as the tables turn in the ecological food web, robber flies are prey to larger, cannibalistic robber flies, spiders, assassin bugs and birds.
There are more than 7,000 species of robber flies worldwide, 1,000 in North America and approximately 250 species in Texas.
Cute but not cuddly; if handled, they can deliver a painful bite geared to their predatory lifestyle – injecting digestive enzymes and painful venom.
Although generalist insect hunters, it’s not all bad; they also eat pest insects and invasive ones. And they aren’t known to carry or transmit diseases.
Robber flies don’t usually hunt at night but they will come to lights at night for insects like other predators, according to information on BugGuide.net. They are most active during the hottest parts of the day and shelter in vegetation at night.
Bee flies
Poecilanthras lucifer, is one of two bee flies I observed for the BioBlitz.
Don’t be turned off by the species name, lucifer, its original Greek meaning is charcoal and references the often-black color of the adult flies. The original Latin meaning of lucifer is morning star, meaning light-bringing or if you delve further, the black bringer of light.
Bee flies are flies that resemble bees and are usually found resting on flowers. Adults feed on flower nectar and pollen. Bee flies are often more frequent visitors to flowers than bees and may pollinate more flowers. They prefer flowers that are purple, blue, violet and white and less attracted to yellow, reddish or pink flowers. Although I have found them on the yellow flowers of skeleton leaf golden eye, Viguiera stenoloba as often as I have on the white flowers of turkey tangle frog fruit, Phyla nodiflora.
Bee flies, as their moniker denotes, imitate bees, but are unlike them as they have only two wings instead of four, large eyes and skinny long legs. As fliers, they can hover in midair, move very fast and maneuver with great skill, changing directions in the blink of an eye. They sip nectar through a proboscis. Pollen sticks to their furry coat and is easily transported to other flowers. They are good pollinators and do no harm.
Signal flies.
Their wings are in almost constant motion, as though giving signals like signalmen on Navy ships. Signal flies are most common in the tropics, according to BugGuide.net
Adults are attracted to flowers, decaying fruit, excrement, sweat and decomposing snails. Larvae are found on fresh and decaying vegetation, carrion, human corpses and root nodules, according to BugGuide.net. Body colors often have a distinctive metallic luster. The face and wings are usually patterned with dark spots or bands. The head is large and has two orbital bristles.
Signal flies eat rotting tree trunks, bulbs, roots, fruit, dried flowers, dead grass stems, dung and fungus. Male signal flies eat rotting fruit, nectar, and the honeydew produced by aphids and leafhoppers. Females also need protein from carrion, including dead insects, bird droppings or frass to support their reproductive activity, according to an online uwm.edu/field-station.
Soldier Flies
The adult black soldier fly, Hermetia illucen, somewhat resembles wasps but has no stinger and is harmless. They are about 5/8-inch long, black flies with smoky black wings. Wings are held over the back when at rest and in death as in the photo of one I found on the lid of our trash bin.
There are far fewer nuisance flies around when black soldier flies are present since the soldier flies devour the larvae of other species, according to a ucanr.edu article by author Alison Collin.
The common name of soldier fly refers to their colors resembling military uniforms, according to BugGuide.net. The flies themselves don’t step out smartly sporting military creases on their colors; as a group, they are fairly sluggish, benign flower-loving flies that can’t bite and don’t have a stinging mechanism. Soldier flies vary in color from black to metallic blue, green and purple or black and yellow patterns.
They are not pest nor nuisance flies. They are harmless to people, and serve a beneficial role in helping decompose garbage and filth. In some places they even help control more noxious insect pests, like house flies.
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