Spiders: Insect Invaders

Spiders: Insect Invaders

The black widow, seen here, appears to be responsible for the majority of spider bites that have been recorded.

Photo: Photos.com

The itsy-bitsy spider
Climbed up the water spout.
Down came the rain
And washed the spider out.
Out came the sun
And dried up all the rain
And the itsy-bitsy spider
Climbed up the spout again.
--Nursery rhyme

Most of us remember that little nursery rhyme from childhood, accompanied by hand and arm gestures. It evokes a picture of a cute little spider that has no desire to do harm; he just wants to have a safe place to rest in the water spout. Fortunately for us, this is an apt description for the vast majority of spiders that exist in the world. They mean no harm to anyone or anything except flying and crawling insects that constitute their food supply. Unfortunately, there are a few spiders that, although they might mean no harm, are capable of inflicting pain and suffering on humans and horses alike.

It is estimated that there are 30,000 to 40,000 species of spiders in the world. Of this number, only about 100 are known to bite. The number shrivels even more when we consider the fact that in the United States, only a very few are considered to be poisonous. Primarily, they are the black widow and the brown recluse spiders.

TheHorse.com Poll: Has your horse ever been bitten by a spider?

Not that I know of 65% (270)
Yes 22% (90)
No 13% (52)

Although they are poisonous or venomous, depending on one's interpretation, it is rare that even these two spiders cause serious injury via bites. When they do, however, it can be painful and potentially harmful to the good health of horses and humans.

Because the black widow and brown recluse are found in many parts of the United States, we will focus on them and the damage they can cause.

Ick! Spiders!

First, we must know just what we are talking about when we discuss black widows and recluses. Sources for this story will range from a veterinarian to information from various research institutions, such as Kansas State University, that have studied biting spiders. Along the way, we will meet two people heavily involved with horses who suffered serious injury from spider bites. We will listen to what a former state veterinarian has to say about spider bites and learn that they might not be as rare as we think--some just aren't diagnosed. He also will tell us what a horse's reaction is, in general, when bitten by a poisonous or venomous spider.

From the outset, we must understand that spiders, basically speaking, do not possess venom to inflict injury on humans and horses. Venom's prime function is to paralyze insect prey so the spider can dine on them.

The Brown Recluse

Much of the information on the brown recluse spider is based on human experiences, rather than from horse cases. The information that follows is from a variety of sources, including the Kansas State University Entomology department and Richard Kaae's Encyclopedia of Entomology.

The brown recluse, also known as the fiddleback or violin spider, has a violin-shaped mark on its back. With legs spread, a brown recluse is about the size of a quarter. The bites of these spiders are generally not as deadly as that of the black widow, and the reaction to the bite generally is local rather than systemic.

The bite initially is described as being quite painless, but leaves two small puncture wounds. Usually within a short time, a cone-shaped sore appears that rapidly gains a white crater at the tip. The bite is surrounded by swollen, red tissue that enlarges continuously. The white tip turns black as tissue dies, but there is little or no pain involved.

Immediate treatment is necessary because the spider's venom will continue to destroy tissue if not treated. Treatment includes administration of antibiotics, pain medications, antihistamines, and possibly removal of dead tissue to reduce the chance of secondary infections.

The brown recluse is most active with the onset of warm days in spring when it begins searching for insect prey during evenings, mornings, and nights. During the day, the brown recluse hides in cracks and crevices in the floor, walls, doors, or windows.

Spiders in general also are active in the fall when they move into barns and other shelters for protection from the oncoming cold of winter. The brown recluse does not seek out people or horses to bite. In fact, it is very shy--thus the name "recluse"--and avoids large animals and people. Bites occur when the spider comes into contact with human or horse and is in danger of being killed, such as being stepped on or rubbed against a wall, or the spider has been surprised and doesn't find an immediate escape route. When one does bite a person or animal, the bites cause problems only about 10% of the time.

The Black Widow

The black widow appears to be responsible for the majority of spider bites that have been recorded. Only the female bites. She is glossy black with a body approximately one-half inch in diameter, a leg span of about two inches, and a characteristic red hourglass mark on her abdomen. The red hourglass marking is a warning coloration that serves notice to predators that she is poisonous. When in her web, she hangs upside down in such a way that all can see her warning coloration.

The black widow spider is found in woodpiles, sheds, basements, and outdoor privies. In fact, outdoor privies used to be a favorite nesting place for black widows, and numerous bites to the posterior portion of the human anatomy were reported. With the advent of indoor plumbing, the number of reported black widow spider bites declined. Areas that are damp and dark attract black widow spiders.

Black widow spiderlings have a clever way of finding new homes. Once hatched, they crawl up on a twig or other structure and expel long threads of silk from their spinnerets. Air currents then float the threads and spiderlings away. They rise with warm air currents and descend when the air cools. If they land in a hospitable environment upon descending, they thrive. If not, they die.

As is the case with the brown recluse, the black widow does not go looking for trouble. However, if surprised or placed in a compromising situation, her reaction is to bite. That bite can cause a serious reaction in some humans and horses that are sensitive to the venom.

Reactions to Bites

Most spider bites to horses, says Jim Logan, DVM, of Riverton, Wyo., formerly Wyoming's state veterinarian for 10 years, are to the muzzle or head area. This seems to indicate that the spider, in at least some instances, was surprised while on the ground or in a location accessible to the horse's head and muzzle.

Most often, Logan says, the reaction to the bite is local, but it also can be systemic. A systemic reaction could involve breathing difficulty and breaking out with hives.

There are many variables involved in a horse's reaction to a spider bite, Logan says. The variables include sensitivity of the horse, the amount of venom injected, and the type of spider involved.

Unfortunately, Logan adds, it is rare when one finds and captures or kills the spider that did the biting. The spider bites, then escapes the vicinity. Because of this elusive characteristic, Logan says, spider bites might not be as rare as we think--they just are not diagnosed because the spider is never found.

"I think that there are a fair number of spider bites that never get diagnosed," he says.

If a spider bite is suspected, Logan says, the first step is to call a veterinarian for advice or have him or her examine the horse so that a definitive diagnosis can be made. In horses, he says, the treatment of choice might involve antihistamines or dexamethasone.

Often, Logan says, the bite will cause an itching reaction in the horse as well as the area being tender to the touch. An abscess usually forms in the dead and dying tissue, and if the horse is allowed to rub the affected area, the abscess might grow larger.

In rare cases, Logan says, it might be necessary to perform localized surgery to remove the necrotic tissue and prevent venom from doing damage to healthy tissue in the area of the bite.

There also is an anti-venom serum (for black widow bites) that can be administered if a horse becomes seriously ill, but some horses have an adverse reaction to it and, in that case, the "cure" becomes as much of a problem as the ailment.

Although spider bites don't fall into the "emergency" category for horses, they do demand immediate veterinary attention. If unattended, the venom from a spider bite can cause continued and ongoing tissue damage that might ultimately require surgery. If treated early, the spread of venom can normally be halted with the administration of appropriate drugs and topical medication.

Cases In Point

Let's meet two individuals heavily involved with horses who apparently were bitten by spiders and suffered severe injury as a result. Their stories are important because they underline the fact that while spider bites normally aren't serious, they can be.

Roy Carter is a very successful cutting horse trainer in Texas. A couple of years ago, he was campaigning a horse that had demonstrated great potential and was poised to make a run for the championship at a major cutting. Shortly before the major competition, Carter developed soreness in one of his legs. Ultimately, it became so serious that he had to find someone else to ride his horse in the hallmark event. Doctors didn't immediately diagnose the problem as a bite from a brown recluse spider. While they were seeking a definitive diagnosis, the spider's venom was spreading and destroying tissue in the leg.

Once the problem was diagnosed, surgery was performed to remove necrotic tissue. The first surgery didn't get the job done and a second surgery was performed. For a time, Carter was quoted as saying in a cutting horse magazine article, there was danger that the leg would have to be amputated to save his life.

Fortunately, that didn't occur. Today, Carter is back in the cutting arena, going full bore with two healthy legs.

The other person to sustain serious injury from a spider bite is Gypsie MacSweeney of Florida. Her story was told by Robert King, a staff writer for the St. Petersburg (Florida) Times in a May 31, 2002, article. We recall it here because it, too, demonstrates the severity of problems that can result from spider bites.

Gypsie was 17 years of age and a horse enthusiast. She trained her own horse and the highlight of her year was winning four ribbons at the county fair--one in each of the classes she entered. She was working with a horse trainer and had dreams of becoming a trainer herself. Her teachers in high school described her as a bright, model student.

Then one day, Gypsie complained of a sore ankle. She thought it was the product of a sprain she had sustained a few months earlier. However, when the pain didn't go away, her mother took her to the emergency room. Doctors there decided that she should be examined by an orthopedic surgeon. He thought it was a sprain. He prescribed pain medication and two weeks of rest.

Nothing helped. The swelling increased and the ankle began turning black. It became an emergency when Gypsie slipped into an unconscious state and was rushed to the Moffit Cancer Center in Tampa. There, an orthopedic tumor surgeon examined the girl and decided he was not dealing with cancer. Tests revealed that Gypsie had an infection so aggressive that it had spread from her ankle into her bloodstream.

Two surgeries were performed, and it was found that the infection had been eating away bone, muscle, and tendon. Some of the tissues were dead. The conclusion was that Gypsie had been bitten by a brown recluse spider. Later, it was found that her family's barn harbored a great many brown recluses.

Gypsie recovered, but was left with a leg that couldn't function quite like its healthy counterpart. Her story points out the importance of prompt treatment for both human and horse when a spider bite is involved.

It also points out the need for vigilance and good husbandry. Areas that are hospitable to spiders, such as woodpiles, should not exist near paddocks or stalls. Barns should be examined regularly for spiders and should be kept clear of containers and debris that can provide them protection and a place to nest.

About the Author

Les Sellnow

Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.

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