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Beware of the black widow

July 1, 1993

Beware of the black widow

By Robert A. Hedeen, Naturalist

I was not all surprised the other day to read an item in the Rockford daily paper about a black widow spider being found this past July behind the Rockton cemetery. In the little over three years I have lived in the Rock River Valley, I have not seen one locally, though I admit I have not been especially looking for one. But, during the 11 years I previously lived in the Chicago area, I encountered this beast on several occasions.

Of all the many species of spiders found in the United States, only two are dangerous to man. It should be noted, however, that all spiders produce venom that they inject with a pair of sharp fangs, but only the toxins of the black widow and that of the brown recluse or fiddleback are apt to cause serious reactions in humans.

The black widow spider is common in the southern and southwestern United States and is found in lesser numbers in the other lower 48 as well as parts of southern Canada. Two species of widows occur in this country: Latrodectus mactans being the type most widely distributed, and Latrodectus geometricus confined (as far as is known) to southern Florida.

The black widow is so called because the female is coal black in color, and she has the bad habit of envenomizing and eating the male with which she has just mated. In some areas, the black widow is called the shoe-button spider because the globose abdomen of the female resembles an old-fashioned shoe button. In addition, the female black widow is readily identified by the presence of a deep red figure on the underside of the abdomen that more or less resembles an hourglass. The innocuous male of the species lacks these diagnostic features and is quite harmless as its fangs are incapable of penetrating human skin

Black widows are found under rocks, in piles of wood, in garages and basements, in outdoor privies, and in almost any other secluded place.

In former days, when the “outhouse” was a common feature of rural dwellings, numerous bites of unsuspecting people were recorded when the facility was used. The bites usually occurred on a delicate portion of the victim’s anatomy. A black widow is not aggressive and is not apt to bite unless one brushes against her web or she has, which happens on rare occasions, set up housekeeping in clothes or shoes that have not been worn for a considerable time.

But make no mistake about it, the bite of a black widow can be serious. Each year in the United States, it is estimated that from 50 to 100 confirmed deaths occur as a direct result of her bites. And, it is safe to assume additional deaths occur that are not recorded in morbidity reports. Shortly after being bitten, a person experiences board-like rigidity of the abdominal muscles. This condition may be promptly alleviated by the injection of calcium gluconate, or a similar muscle relaxant

After being fertilized by the male, the female spins an egg sac around the hundreds of eggs she lays. One reason black widow spiders are relatively rare is that the mother spider dines on any of her offspring she can catch, and the stronger spiderlings have the nasty habit of devouring their weaker siblings—survival of the fittest!

Some years ago, when I was assigned to the faculty of the Army’s Medical Field Service School in San Antonio, Texas, my colleague, Major (Dr.) Hugh L. Keegan, and I conducted research on the relative toxicity of Latrodectus mactans.

By using a very low voltage of electricity, we extracted venom from female black widows. White mice were exposed to various concentrations of venom, and it was possible to determine the exact LD-50 concentration of venom (lethal dose required to kill 50 percent of the test subjects). Using the same procedure with commercially procured venom of the western diamondback rattlesnake, we found the venom of the black widow, calculated dry weight to dry weight, to be about 50xs more potent than that of the rattler. The article referring to the finding of a black widow near Rockton stated black widow venom was 15xs more toxic than that of a prairie rattlesnake. I doubt if there is that much difference in the toxicity of the venom of the prairie rattlesnake and that of the western diamondback

Of course, one must realize that when a person gets a shot of venom from a fully loaded rattlesnake, he is being injected with considerably more poison than if he were bitten by a black widow. The bite of a rattlesnake is, therefore, much more dangerous than that of a widow. The primary reason the spider’s venom is much more toxic on a weight-weight basis is that it is neurotoxic in nature and affects the nervous system of the victim. The venom of the rattlesnake and other pit vipers is hemotoxic in action, affecting the circulatory system and is not as potent

It has been suggested the female of the species is far more dangerous than the male, and that is certainly true in the case of the black widow.

Maintaining any venomous animal as a pet is to be discouraged.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960-1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

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