Signal Fly – Platystomatidae

I found this signal fly resting on a leaf in my garden near the kitchen compost pit. I used Canon EOS 5D Mark III with Canon MP-E 65mm f/2.8 1-5x Macro at 2X magnification. I used Canon MT-24EX macro twin light flash for illumination. Canon MP-E 65mm Macro Lens is a manual focus lens. This is not a bad thing for a macro-only lens as this is how macro lenses are frequently used anyway. Turning the focus ring does indeed bring the subject into focus, but this effect zooms in and out on the subject. You can either set the magnification you desire and move closer/farther away to focu, or you can change the magnification by turning the ring until your subject is in focus.

Platystomatidae (Signal flies) is a distinctive family of flies (Diptera). Their scientific name is derived from their flat mouth (platy = flat; stomato = mouth) Their common name, Signal flies, comes from their walking style, they exhibit a characteristic manner of movement, include rowing or extending of wings, waving of front pair of legs, move forwards and backwards, extend and raise of proboscis. Signal flies are worldwide in distribution.

Signal flies are small, around 5-6mm in size with patterns on their wings and often on their faces and with metallic colours elsewhere. Adults have the typical vacuum cleaner mouth parts of a fly. In Signal flies this protruding mouth parts resembles more of a gas mask. Adults are found on tree trunks and foliage and are attracted to flowers, decaying fruit, excrement, sweat, and decomposing snails. Larvae are found on fresh and in decaying vegetation, carrion, human corpses, and root nodules. Male Signal flies eat carbohydrates in the form of rotting fruit, nectar, and honeydew produced by aphids and leafhoppers. Females too eat the same stuff, but they also need protein from carrion (including dead insects), bird droppings or frass (insect poop) to support their reproductive activity.

Signal Flies strut and wave their wings during courtship. After their brief courtship (he may feed her droplets of clear, regurgitated liquid while mating), the female lays her eggs on plants, mostly Legumes. Legumes, are called “nitrogen-fixing” plants; certain soil bacteria living in nodules on the plant roots accumulate and transform the nitrogen. The nitrogen feeds the plant and the plant feeds the bacteria. When a plant dies, other bacteria assist in decomposition, releasing the stash of nitrogen to nearby plants.

When the Signal Fly eggs hatch, the maggots of many species head for the nitrogen-fixing nodules on roots and chew their way in (the larvae of other species are saprophagus, feeding on decomposing plants or animals). Once inside, Signal Fly larvae feed on (and damage) the root nodules, inadvertently crippling the nitrogen-fixing factory. A big population of Signal Fly larvae could affect plant growth, but they are only listed as “minor crop pests.”