Friday, May 23, 2014

Syrphid Flies

Syrphid Fly: also known as a Flower or Hover Fly. 

      Syrphid Flies are a family of 6,000 or so flies in the Order Diptera of insects. They are best known for being bee mimics. By looking like bees or wasps, many predators avoid them thinking they might get stung, although they are actually harmless and incapable of stinging. They also mimic bees in being important pollinators of flowers as well.  After bees, flies are considered the next best animal pollinators. Of the many kinds of flies, Syrphid flies are considered the family of flies responsible for the most pollination. This is why they are sometimes also called Flower Flies and Hover Flies (for hovering around flowers). A closer look however reveals they have only 2 wings (not the 4 of bees/wasps), very short antennae, and huge eyes, unlike the long antennae and smaller eyes of bees/wasps. Diptera, the Order of animals representing all true flies, actually translates to "2 wings".

A Flower Fly with its typical big fly eyes and single pair of wings stares out while feeding on a Tickseed.

     Worldwide, flies are now being recognized as extremely important pollinators, second only to bees. At least 71 families of flies have been documented visiting flowers, but none are better recognized for this pollination trait than Syrphids. Unlike bees, of which 20% are oligilectic, meaning they require the specific pollen of certain flowers they evolved with in order to be able reproduce, flower flies are generalists and are not thus tied down or their range limited by the presence of specific pollen host plants. This means they can travel far and wide and visit a wide variety of flowers. In fact, in some places like the British Isles, they can be migratory, even crossing the open water from mainland Europe to visit and range over a wide array of habitat conditions. As they don't need to accumulate food stores for their young, they may also able to survive with less resources available in general, and also seem more tolerant of moist and cold conditions. Some studies in Germany have shown that 80% of the flowers in some regions were visited by flower flies. Syrphid flies are now being recognized world wide as vital to agriculture and flower pollination.
     Now our native flower flies may not be as far ranging as the British migratory ones, but are still extremely valuable. In Colorado, 65% of flowering plants were visited by Syrphid flies for example. Over 813 flower fly species are recognized in North America, many poorly studied and many quite diverse and beautiful, particularly in their mimicry of bees.

Syrphid Fly maggot (larva)

     Although I had often noticed Syrphid Flies around flowers, I really got acquainted with them one day when I was working the gardens at a nature center and noticed a slug-like creature among a large congregation of aphids. The way it ate its prey was fascinating: it would rip an aphid off the plant, hold it over its head and eat it alive. The whole time the aphid would be kicking its feet frantically in the air while being devoured.

A Syrphid Fly maggot eating an aphid

     Being curious, I raised the creature, amazed at the huge amount of aphids it consumed each day. Soon it pupated and what emerged was a beautiful Syrphid Fly. I did some research and now realize how valuable they can be in a garden. Not only are Syrphid Flies often considered the second best pollinators in the world after bees, but many species are also valuable as biological controls. By feasting on many insect pests such as aphids (up to 400 of them before changing into an adult), they perform yet another valuable function for us in our yards and gardens. Many are beneficial in both ways, and are fascinating mimics as well, being wonderful additions to our gardens and yards.

A Syrphid Fly laying eggs among aphids on a Cupplant

     While there are some Syrphid larvae that feed on decaying vegetation and other things, but it appears the vast majority feed on other small insects and are widely now considered both biological control agents and pollinators. So the next time you see what looks like a bee or wasp hovering in front of a flower, or some slug like creature amongst the aphids, you may actually be looking at these fascinating and beneficial creatures.

The Flower Fly Meromacrus acutus , thought to be a yellowjacket mimic

Tuesday, May 20, 2014

Broken Wing?


Killdeer with "broken wing"

     Today I was called over when staff noticed a bird that appeared injured in our plant nursery. I recognized the bird by its double neck-band and rufous rump as a Killdeer (Charadrius vociferus), a type of plover (shorebird) that frequently nests well away from water and shores. I also recognized what it was trying to do.
     Killdeer are well known for their distinctive "kill-deer, kill-deer" call and their broken wing act. This bird was pretending to be injured so as to a lead a potential predator (or human in this case) away from its nest. Since it had chosen a heavily traveled location full of moving equipment, I needed to find its nest and then protect it as soon as possible. That is a task easier said than done since the eggs are extremely well camouflaged. 
     It took a surprisingly long time to find the eggs, they so well matched the rocky ground, next to a discarded pen no less. Having found them, we marked off the area and did what we could to protect them despite their location. Another interesting aspect that Killdeer eggs display is their pointy shape. This adaptation is common among cliff birds and others who do not build much of a nest. By being pointy, the eggs tend to roll in a tight circle should the parents bump into them or they otherwise are nudged. This keeps them safe and close together. Killdeer eggs are not as extremely pointy on their end as others, but you can still notice the difference. 

Killdeer nest

Killdeer eggs
   This made for an very interesting and unexpected discovery in such a well traveled and active work site. Hopefully we have done enough to allow the eggs to hatch in about 3 weeks and have the parents lead the precocial young to a safer location. 

Monday, May 19, 2014

Bird Food for Thought

A Common Grackle loaded with caterpillars for its young.

     Many birds are now nesting in our area. Many others are continuing their journey North but make important pit stops here to gather strength and gas-up on food for their long journey. The first couple of weeks of May are often considered the peak of migration for the DC metropolitan region. The reason for this has to do with the emergence of insect food to sustain them. Indeed, some 96% of terrestrial birds feed on insects and other invertebrates. It could be said that we owe the phenomenon of migration to the insects emerging this time of year.
     Even some birds that we normally think of as feeding on other things provide insects to their young for the protein they need to grow, including hummingbirds. Other birds, such as warblers, are almost exclusively insect gleaners. No insect group provides more of this food than the caterpillars of moths and butterflies. Their abundance this time of year is the primary reason for our richness in bird life during this season. The vast majority of caterpillars born end up as food for birds and other animals. In fact, all our bats eat insects, and the moths that most caterpillars turn into are their favorites.
    So the next time you see a caterpillar or bump into one dangling from a silken thread, remember all the animals that depend on it. Of course the caterpillars do not want to be eaten and have a myriad of ways to protect themselves, but that is food for another Blog...

Wednesday, May 14, 2014

The Legend of Flowering Dogwood

     Flowering Dogwood has always been known for its strong and durable wood, being used for golf club heads and mallets for example. It usually is too short and twisted however to make more substantial objects. There is a Christian legend regarding why Flowering Dogwood is the way it is.
     At one time, it is said, the dogwood was taller and stronger than most trees. Because of this, it was supposedly chosen to fashion the cross that was used to crucify Jesus Christ. This so shamed the dogwood that it begged Jesus for forgiveness for serving in this role. Jesus did not blame the dogwood, but decided that the tree from then on would only grow as a much smaller and twisted tree, never again suitable for crucifying anyone.
     As a permanent reminder of its original role however, the flowers were also forever changed. They would now bear four "petals" (bracts actually) in the form of a cross. The center of the flower would also now resemble a crown of thorns, and each petal-like bract would also bear the marks of the nails used in the crucifixion, often stained near their edges reminiscent of the blood that was spilled. As they age, the beautiful white of the "petals" often  have dark drops that appear on them, looking like dried blood as well. So it is that to this day, the Flowering Dogwood is a short and twisted understory tree, but with beautiful, if symbolic, blooms, at least according to this legend.

Tuesday, May 13, 2014

Virginia's State Flower and Tree

Virginia's state flower and tree - the Flowering Dogwood.

    Flowering Dogwood (Cornus florida) is both Virginia's state flower and tree. It serves as the state tree of Missouri and state flower of North Carolina as well. Flowering Dogwoods grow in the understory, rarely over 35' tall, with opposite branching. They are in peak bloom in our area right about now, the actual flowers themselves being quite small, but the "petals" (actually bracts) attracting a lot of attention. If pollinated, they form bright red fruits called drupes. The fruit changes color and matures at the same time that the leaves change color. 

Flowering Dogwood fruit, technically drupes.
      This is something referred to as "fall foliar fruit flagging." The bright fall color "flags" birds down who then are able to find the fruits. This gives the short tree an advantage, standing out and having its drupes eaten and seeds dispersed instead of getting overlooked among the taller forest trees. This is a strategy many fall fruiting shrubs use. The leaves themselves decompose faster than most others, returning their nutrients quickly back into the soil.  Flowering Dogwood also has very distinctive turban-like flower buds in winter, which along with the opposite branching and alligator-like bark, makes identification of this tree fairly easy.

Flowering Dogwood opposite leaves and Fall color.

     The drupes are an important and favored food for birds, being high in fat content. Unfortunately, a fungal disease called Dogwood Anthracnose is spread very easily this way, being picked up by the bird in migration when it stops to eat and then transferred further along the migration route to yet other Flowering Dogwood trees when the bird lands again. This is killing a high proportion of them and was likely brought over in the horticultural trade on Asian Kousa Dogwoods which are resistant to the fungus themselves, but can act as carriers and infect the natives.

Flowering Dogwood's turban-like buds in winter.

     Flowering Dogwood has a deep ethnobotanical history. Native American Indian tribes made considerable use of it. The Cherokee, among other tribes, for example chewed the bark for headaches, and used other parts to treat for fever, diarrhea, measles, and intestinal worms. The twigs could be used for toothbrushes of sorts and had a reputation for whitening teeth among not just the indigenous people but Africans whether slave or free, and throughout the South. During the Civil War when the Confederacy was particular short on supplies, Flowering Dogwood was officially sanctioned by Porcher in 1863 in their official ethnobotany manual as "one of the most valuable of our indigenous plants." It was used by the South in many of the same ways as by the native peoples, but also as a substitute for Peruvian quinine in treating malaria, as a dye, for stomach issues, for durable hand tools, and was preferred in the manufacture of gun powder. One version of how it received its common name refers to its supposed use in treating dog mange, thus "dogwood." Others say the name is derived from the "dags" or dagger-like skewers when people used them for cooking. "Dagger-wood" eventually turned into Dogwood.
     As you can see, there is much more to this plant than just it's good looks. It serves as the caterpillar host plant to 112 different butterfly and moth species. Over 98 sepcies of birds have been documented eating its fruits. Whether in its roles in feeding our wildlife or traditional medicine, this is a tree worthy of being a state symbol.

Monday, May 12, 2014

Eastern Tent Caterpillars

Tent Caterpillar web nest.

Tent Caterpillar

     The web nests of Eastern Tent Caterpillars (Malacosoma americana) are now easily visible on woody plants of the Rose family, especially cherry trees. If you see a web nest in the woods during spring around here, it's a pretty good bet you have a Wild Black Cherry for example. The caterpillars emerge rather early in the year and form their web tents where they are safe from many predators who are unable or prefer to not try to get through the thick webs full of frass (insect poop). The caterpillars likely sequester cyanide from the cherry they feed on and have somewhat irritating hairs to also protect them. They tend to feed at night to avoid even more potential enemies. Despite all these defenses, Cuckoos and some wasps still get their share of them. Although numerous, the caterpillars feed early enough in the year to allow their host plants to recover, having evolved with them so that they rarely cause any real harm to the native trees they feed on. It of course makes poor evolutionary sense to permanently kill off the plants you need to survive. They can however sometimes damage nonnative cherries that did not evolve with them, though that's usually uncommon as well. 
     Right about late May or very early June, the caterpillars finish feeding and go on a walk-about looking for a place to form their white, web-covered cocoons. This is when many people notice them crossing roads and trails and make the assumption they are Gypsy Moths. Though similar, the Gypsy Moth caterpillars are smaller this time of year, with big-looking heads in proportion to their bodies and mostly lacking the blue marks along their sides that Eastern Tent Caterpillars have. The Tent Caterpillar cocoons are a favorite target of some birds, with Blue Jays being very adept at finding them, picking through the web and hair-covered outer layer to get to the developing moth pupae inside. The very hairy, brown moths with two light-colored lines that emerge are otherwise rather drab looking. They appear mostly in late June around our region and quickly search for cherry trees and other members of the Rose family to lay their eggs upon to start the cycle all over again.
     By the way, Forest Tent Caterpillars are also often confused for Eastern Tent Caterpillars and are active about the same time. These do not form any web tents, prefer deeper woods, and have an interesting pattern on their backs that look like penguins all standing on top of each other.