Biting Flies and Yucca

I have a large pile of yucca (likely Yucca gloriosa or Yucca harrimaniae Trel. ) to plant. Locally this species is referred to as "Spanish Bayonet." There are 30 species in Yucca which occur in the United States. . .so it is difficult to say for sure what my pile-o-yucca might be. I retrieved it from a trash pile.

All species of yucca are in the Agavaceae or Century-plant family.

Spanish Bayonet is a good name for this plant. Each leaf sports a long, sharp barb capable of inflicting a serious stab to anything that encounters the barb. When I was a kid it was common to see large yucca plants sporting little egg-carton "flowers" that Northerners would cut and place on the spikes, to give the plant a more festive appearance.

I retrieved the yucca to shield juvenile queen palms (Syagrus romanzoffiana) from potential frost this winter. Unfortunately, I cannot get the yucca planted because of all the biting flies. They descend on me for their meal as soon as I walk into the back yard. . .and despite the layers of denim.

It is difficult enough gardening in denim when the temps are in the 90s. . .the biting flies make gardening nearly impossible. I'm pretty sure that our particular biting fly at present is the "Stable Fly," pictured below on a dog. More on all of Florida's biting flies below:

In Florida we have a variety of biting flies. Biting flies attack humans to obtain a blood meal and can be very annoying. Some biting flies are also capable of transmitting disease. Biting flies of importance are sand flies, black flies, stable flies, mosquitoes, horse flies and deer flies.

1. Sand fly (Culicoides).

Sand Flies, often called "punkies," "no-see'ums," or biting midges are vicious where they occur. They are often more troublesome than mosquitoes because they can easily enter dwellings through ordinary 16-mesh window screen. The presence of these insects can decrease property values and severely hamper use of recreational areas. Vacationers and campers literally have been driven away from areas by these tiny biters. Sand flies can also cause loss to cattlemen in terms of annoyance to cattle and transmission of various nematode diseases.

Sand flies are members of the insect order Diptera and undergo a complete development with egg, larva, pupa, and adult forms. The adults are less than 1/16 inch long, dark gray to black in color and have one pair of wings which are spotted. The sand flies breed predominantly in salt marshes; however, some species that are found inland breed in fresh water areas and tree holes.
Larvae of sand flies are found in mud, sand, and debris around the edges of ponds, springs, lakes, creeks, and in tree holes or on slime-covered bark. In the water they are free swimmers and are commonly found on floating twigs or leaf trash. The larvae pupate on floating debris or at the water's edge. The adult females, like mosquitoes, require blood to mature the eggs. Males do not bite. Sand fly larvae can be found in marshes the year-round; however, the period of greatest adult activity is June to August.

Sand fly activity is associated with air movement. Adults of most species seldom bite when there is air movement. Sand flies are also sensitive to temperature. Animals having a high body temperature are attractive to great numbers of female sand flies. Persons performing hard labor out-of-doors frequently are severely annoyed by these insects.

2. Black Flies (Simuliidae).

Black flies are small, dark, stout-bodied flies with a humpbacked appearance. The adult females suck blood mainly during daylight hours and are not host specific. The black fly is a potential disease vector in Florida. It hovers about the eyes, ears, and nostrils of man and animals, often alighting and puncturing the skin with an irritating bite. Black flies are not considered to be major pests of homeowners in Florida.

The black fly life cycle begins with eggs being deposited on logs, rocks, or solid surfaces in swiftly flowing streams. Larvae attach themselves to rocks or vegetation with a posterior sucker. The length of the larval period is quite variable depending on the species and the larval environment. The adults which emerge after pupation are strong fliers and may fly 7 to 10 miles from their breeding sites.

3. Stable Fly.

The stable fly, also known as the 'dog fly' or 'biting house fly,' is a blood-sucking fly which closely resembles the house fly. It is similar to the house fly in size and color, but may be recognized by its sharp, piercing mouthparts which project forward from the head. Unlike many flies, both sexes of the stable fly are vicious biters.

The fly is a common pest of man and animals throughout the world. In Florida -- especially western Florida -- stable flies are a serious pest of man and have been a severe threat to the tourist industry.

Stable flies are very persistent when searching for a blood meal and may be easily interrupted in feeding. They may be mechanical vectors of animal diseases but are not considered effective in spreading human disease.

Stable flies breed in soggy hay, grain or feed, piles of moist fermenting weed or grass clippings, seaweed deposits along beaches, and manure. When depositing eggs, the female will often crawl into loose material, placing the eggs in little inner pockets. Each female may lay a total of 500 to 600 eggs in four separate layings. The eggs will hatch in 2 or 5 days, and the newly hatched larvae bury themselves, begin to feed, and mature in 14 to 26 days. While the average life cycle is 28 days, this period will vary from 22 to 58 days, depending on weather conditions. The adults are strong fliers and range many miles from the breeding sites.

4. Horse Flies and Deer Flies.

Horse and Deer flies are closely related insects with similar life cycles. Both horse and deer flies are strong fliers and only the female bites. They are daytime feeders and can easily cut the skin open for a blood meal. While feeding an anticoagulant is injected into the wound and causes the blood to flow freely. Many people are allergic to horse fly and deer fly bites. Also, wounds are excellent sites for secondary infection. Since they are intermittent feeders, horse and deer flies are important transmitters of animal diseases.

Most species of horse and deer flies are aquatic or semi-aquatic in the immature stages. Some will also develop in moist earth, leaf mold, or rotting logs. Generally the eggs are deposited in layers on vegetation, objects over water, or moist areas favorable for larval development. The eggs hatch in five to seven days and the larvae fall to the water surface or moist areas where they begin to feed on organic matter.

Many species feed on insect larva, crustacea, snails, and earthworms. When the larvae are ready to pupate, they move into drier earth usually an inch or two below the soil surface. The pupal stage lasts two to three weeks, after which the adults emerge. The life cycle varies considerably within the species, requiring anywhere from 70 days to two years.