FRIENDS OF EDGEWOOD NATURAL PRESERVE
|
FRIENDS OF EDGEWOOD NATURAL PRESERVE
|
|
|
EDGEWOOD FLIES THAT YOU MIGHT LIKE by Paul Heiple
Whenever one thinks of flies, it is usually an unpleasant image that comes to mind—decay loving pests that spread disease and filth. And those people who also know that mosquitoes and gnats are flies, can add “bloodthirsty” to the list. All of these are insects that can make life in the out-of-doors miserable. However, this article is to show that not all flies are bad. A group you may not even recognize as flies is actually beautiful, and for most of the species in the group, completely beneficial. These flies are the hover flies, members of the family Syrphidae. The Syrphid flies are so varied that it seems only two statements can be made that cover all the species: they have a false vein in their wing that is only pigment, and they commonly hover in the air completely motionless except for their wings. Other than that, they vary from small to moderately large flies, are usually brightly colored, and may or may not be hairy. Many so resemble bees and wasps, it can require a careful look to tell the difference. The flight pattern of these insects is very distinctive: so much so that they can be identified even from very blurry videos. Such was the case at Jasper Ridge, Stanford's biological preserve located between the towns of Woodside and Portola Valley. Web Cam videos were taken of the Western Leatherwood plant to see what species pollinated the flowers. The small dot that flew into the picture was easily identified as a Syrphid fly because it flew in quickly, stopped in midair, and then approached the flower. This video also showed that these flies are active all year round, since the Western Leatherwood flowers in January and February. The adult Syrphid flies feed on nectar and pollen, (which gives them another common name, the flower fly). This makes them one of those native pollinators that are so often ignored but are so very important to native plants. The larvae of these flies are even more varied than the adults. One of the most common types of Syrphid fly larvae is a predator that feeds on soft-bodied insects such as aphids. This larva often looks like a headless caterpillar, and is frequently green with white or yellow strips, which make it blend in with a plant's stem. It hunts by tapping about the stem like a blind person with a cane, moving back and forth in an arc, and then moving forward a bit to tap out another arc. When it encounters prey, it uses a hook in its mouth to grapple its victim and lift it off the plant stem. And then, as it prefers its meal in liquid form, it sucks the juices out of its prey before casting the drained body aside and moving on to repeat the process with the next victim. One larva can eat hundreds of aphids during its two-week growth period.
Syrphid fly larvae that are not predators are plant feeders and scavengers, but they have little else in common with each other. One plant-eating group has taken to eating bulbs, and, like most fly larvae, looks like white maggots. Another larva scavenges in the nests of social insects such as ants, and is round and flat. And yet another lives and feeds in polluted water so low in oxygen, it has evolved a long tail that it sends up to the surface of the water and through which it breathes. It is estimated that there are over three hundred species of Syrphid fly in California. I have not collected all these species locally, so I do not have an estimate on how many are actually here, but I do know I have seen at least ten very distinctively different Syrphid flies in this area. For those of you who want to look for these flies, watch for the adults around flowers. See if you can pick up the clues that indicate they are not bees or wasps—look for two wings, short antennae, and large eyes with straight-line sides along the back of the head. As for the larvae, they are often found with groups of aphids—look for elongated forms near the aphids as well as lots of liquid-free aphid skins. |
|
