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Arizona has no tigers of the mammalian variety (we do have mountain lions, bobcats, and very rarely, jaguars and an ocelot or two), but we have insects that richly deserve the sobriquet. I’m talking about Robber Flies.
Robber Flies are members of the Asilidae family of insects and they are cousins of other true flies. There are about 7000 species of Robber Fly worldwide. They are fond of hot, dry environments with sandy soil. In other words, southern Arizona is an ecological paradise for Robber Flies.
They are extraordinary predators. A half-inch (about 1.25cm) Robber Fly is perfectly capable of assaulting and subduing a dragonfly several times its size. A Robber Fly’s hunting style is to perch quietly, waiting for an unsuspecting insect to fly close, and then to pounce. It seizes its victim in mid-air, stabs it with its long, chisel-shaped proboscis, injects a highly toxic venom that kills almost instantly, and then retreat backs back to its original perch to enjoy its meal. Robber Flies have no fear of attacking wasps and bees. In fact, just about any flying insect is fair game for one of these terrors.
The other day I came across a Robber Fly as it perched, undoubtedly waiting for prey to come along.
The fly was unconcerned about my presence. It sat quietly, as I maneuvered within a few inches of it in order to take its picture. After I took a few pictures the fly disappeared from my viewfinder. I looked up from the viewfinder to discover that the fly had landed on my camera’s prism housing, about three inches from my forehead, and was quietly sizing me up. I stood back and watched it for a few seconds, whereupon it calmly flew back to the bush on which it had been perching.
I’m not sure what was on this fly’s mind. Robber Flies aren’t known for gratuitously attacking people. However, they will defend themselves if molested and their bite is supposedly legendarily painful. I wondered if this fly was viewing me as an enemy.
Probably not. There’s a better explanation for its behavior. Many insects can sense carbon dioxide emissions produced by respiration. Bees and wasps, for example, sense the presence of a human by detecting the carbon dioxide in his or her exhaled breath. Its at least possible that this fly had sensed my presence from the carbon dioxide I was exhaling and moved in to check me out. It lost interest when it discovered that I wasn’t edible.
If you examine these images closely you’ll see that the fly’s face is covered with long whitish hairs, giving the fly a bearded look. No one knows to a certainty why Robber Flies sport all of these hairs but one explanation is that they protect the flies from struggling prey. Notice also that the fly’s second leg on the right hand side of its body appears to be amputated at the first joint below the fly’s thorax (its “knee”). The fly seemed not to care. Its leg undoubtedly was a casualty of its swashbuckling lifestyle.
Images made with a Canon 5DS-R, 180mm f3.5 L Macro Lens, illuminated by Canon Ring Light, stabilized by monopod, M setting, ISO 100, f13 @ 1/160.
Sonoran Images 