What is a robber fly?

Robber flies (family Asilidae) are a large family of predatory flies with over 7,000 species worldwide and hundreds of species in Arizona. They range from 3–50mm in length and are characterized by a bearded face (mystax — a tuft of bristles that protects the eyes during prey capture), a stout, tapering abdomen, and powerful legs with spiny tarsi for gripping prey. They are aerial predators that catch other insects in flight, inject paralytic saliva, and consume the liquefied contents of their prey.

Are robber flies dangerous to humans?

Robber flies can bite humans if handled, and the bite can be painful — their proboscis is designed to penetrate insect exoskeleton. However, they are not aggressive toward humans and will only bite defensively. The bite causes localized pain and swelling but no systemic effects. Avoid handling them, but there is no need to fear them in your yard.

What do robber flies eat?

Robber flies are generalist predators that eat virtually any flying insect they can overpower, including bees, wasps, grasshoppers, dragonflies, beetles, and other flies. They are ambush predators — they perch on exposed surfaces and launch aerial attacks on passing prey. After catching prey with their legs, they inject saliva containing neurotoxic and proteolytic compounds that paralyze and liquefy the prey's internal organs.

Are robber flies beneficial?

Robber flies are important predators in Arizona's desert ecosystem. They help control populations of grasshoppers, beetles, and other insects. Some species prey heavily on bees and wasps, which can be a concern for beekeepers, but overall their ecological role as predators is beneficial. They are not pests and do not damage plants, structures, or stored products.

How do I identify a robber fly?

Key identification features: (1) Bearded face — a dense tuft of bristles between the eyes. (2) Hollowed-out abdomen — the abdomen appears pinched between the thorax and the wider posterior segments. (3) Powerful, spiny legs. (4) Perching behavior — robber flies sit on exposed surfaces and make short, fast flights to catch prey. (5) Size — Arizona species range from small (5mm) to very large (50mm for the giant robber fly Promachus).

Fly Control

Robber Flies in Arizona — The Aerial Assassin That Hunts Bees, Wasps & Dragonflies

Back to Blog9 min readMaricopa & Pinal County

Tree Killer

Palo verde root borer larvae feed on tree roots for 3–4 years, causing progressive decline and sudden tree collapse — often during monsoon winds.

Robber flies are among the most formidable predatory insects in Arizona — capable of catching prey in mid-air, including bees, wasps, and even dragonflies. Here's what makes them remarkable.

Robber flies (family Asilidae) are the apex predators of the insect world. Arizona hosts an exceptional diversity of robber fly species — over 100 have been recorded in the state — ranging from the tiny Dioctria species at 8 mm to the massive Promachus species that can exceed 30 mm in length. All are aerial hunters, intercepting prey in mid-flight with explosive speed and precision. A robber fly spots its target from a perch, launches an attack, seizes the prey with its strong, bristled legs, and injects a saliva cocktail containing neurotoxins and proteolytic enzymes that paralyze and liquefy the prey's internal tissues. The robber fly then feeds by sucking out the liquefied contents. Prey items include bees, wasps, grasshoppers, beetles, dragonflies, and even other robber flies — essentially any flying insect the robber fly can overpower. This predatory behavior makes robber flies valuable natural pest controllers, reducing populations of flies, gnats, and other nuisance insects.

Palo Verde Root Borer Quick Facts

Adult Size

7–10 cm

Larval Stage

3–4 years

Season

Jul–Sep

Host Trees

Palo Verde, Mesquite

Despite their aggressive hunting behavior, robber flies rarely bite humans and are not considered dangerous. A bite can occur if a robber fly is handled carelessly — the same mouthparts used to subdue prey can pierce human skin — but this is uncommon and the result is a sharp, localized pain similar to a bee sting, without venom injection. Robber flies are most active during Arizona's warm months (April through October), with peak activity during the hottest parts of the day when their insect prey is most active. They favor open, sunny habitats: desert scrub, grasslands, roadsides, and the edges of agricultural fields. Many species are cryptically colored to blend with soil, bark, or vegetation, making them difficult to spot until they launch an attack. The larvae of most robber fly species are soil-dwelling predators that feed on beetle larvae, fly pupae, and other soil invertebrates — further contributing to their beneficial role in the ecosystem.

Robber flies are entirely beneficial insects and should not be controlled. If you are seeing large numbers of robber flies on your property, it is a sign of a healthy insect ecosystem and likely indicates an abundance of the prey insects they hunt. The presence of robber flies is actually a positive indicator — they are actively reducing populations of pest flies, gnats, and other nuisance insects. No treatment is warranted or recommended. If you are concerned about a large, aggressive-looking fly on your property and are unsure whether it is a robber fly or a different species, Pest Control Bros can help with identification. We serve Maricopa and Pinal County and offer free inspections — call (520) 424-5244 to speak with a licensed pest control professional who can accurately identify any insect and advise on whether treatment is appropriate.