Good food comes to robber flies that wait
Among insects, robber flies are master predators, unforgettable once you’ve seen one in action.
Rather than chase down their prey, robber flies use a “sit-and-wait” tactic, spending most of their time perched and looking around, ready to take flight at a moment’s notice.
If a potential meal flies by, the fly darts out, extends its strong, spiny legs, and seizes the prey in mid-air. A beard of bristly hairs protects its face from the ensuing struggle.
Next, using its beak-like mouthparts, the robber fly injects saliva into the victim’s body. This secretion paralyzes the prey and breaks down its tissues, whereupon the predator sucks up its liquid meal.
There are some 7,000 species of robber flies worldwide, including about 128 in South Carolina.
Most have elongated bodies, short antennae, and drab coloration. A few species are stouter and resemble bumblebees.
Robber flies are relatives of midges, house flies, and mosquitoes. Like all true flies, they have a single pair of functional wings. The second pair is reduced to two knob-like sensory organs that help stabilize flight.
Females have a sword-like ovipositor, used to deposit eggs in soil or decaying organic matter. The worm-like larvae are also active predators.
Robber flies are common insects, often seen in dry, open, sunny areas during the warmest parts of the day.
Although predatory tactics vary among species, robber flies are versatile, opportunistic hunters, and few insects escape their notice.
Once I saw a robber fly seize a dragonfly much bigger than itself, wrestle with it noisily on the ground, then rise with its heavy parcel to a nearby shrub, where it proceeded to consume its meal.
Robber flies pursue prey of diverse shapes and sizes – from other types of flies to beetles, butterflies, even bees and wasps.
Fortunately for us, unless robber flies are molested, they don’t bite humans.
Vicky McMillan, a retired biologist formerly at Colgate University,lives on Hilton Head Island. She can be reached at vicky.mcmillan@gmail.com.
This story was originally published July 11, 2016 at 7:19 AM with the headline "Good food comes to robber flies that wait."