Longtime residents of eastern Fairfax County, Virginia USA may recall reading about the “Mount Vernon Monster” that reportedly roamed the region during the late 1970s. Although I have neither seen nor heard the monster, I jokingly reply “Bigfoot” whenever people pass me at Huntley Meadows Park and ask whether I shot any good photographs. But seriously, folks — there are real monsters at the park, including horse flies and robber flies.
The following photos show two horse flies, possibly Tabanus calens, spotted during recent photowalks along the boardwalk in the central wetland area. Both individuals are females. Male horse flies don’t bite; females bite, painfully!
Adult horse flies feed on nectar and sometimes pollen. Females of most species are anautogenous, meaning they require a blood meal before they are able to reproduce effectively, if at all. Much like male mosquitoes, male Tabanidae are not ectoparasitic and lack the mouth parts (mandibles) that the females use in drawing the blood on which they feed. Most female horse flies feed on mammalian blood, but some species are known to feed on birds or reptiles. Some are said to attack amphibians as well. Source Credit: Horse-fly, from Wikipedia.
17 September 2014. Photo 1. Horse fly (female).
Males have eyes that meet along a seam down the middle of the head (holoptic eyes); females have eyes that are well-separated. Source Credit: Benjamin A. Coulter, member of the BugGuide group on Facebook.
17 September 2014. Photo 2. Horse fly (female).
The next gallery shows another female horse fly spotted along the boardwalk on 15 September 2014.
15 September 2014. Photo 1. Horse fly (female).
15 September 2014. Photo 2. Horse fly (female).
15 September 2014. Photo 3. Horse fly (female).
The last photo shows a Red-footed Cannibalfly (Promachus rufipes), a species of robber fly spotted near the beginning of the boardwalk.
10 September 2014. Red-footed Cannibalfly.
Robber flies feed mainly on other insects. (Whew, that’s a relief!)
The fly attacks its prey by stabbing it with its short, strong proboscis injecting the victim with saliva containing neurotoxic and proteolytic enzymes which very rapidly paralyze the victim and soon digest the insides; the fly then sucks the liquefied material through the proboscis. Source Credit: Asilidae, from Wikipedia.
There are “approximately 1,040 species of robber flies in approximately 100 genera in our area.” Source Credit: Family Asilidae – Robber Flies, from BugGuide. Thanks to Mike Powell, fellow wildlife photographer and blogger, for identifying the species of robber fly shown above!
Copyright © 2014 Walter Sanford. All rights reserved.