Handbook of Medical Entomology

by William A. Riley; O. A. Johannsen

In spite of their prominence and the fear which they arouse there are few accurate data regarding these American tarantulas. It has often been shown experimentally that they can kill small birds and mammals, though it is doubtful if these form the normal prey of any of the species, as has been claimed. There is no question but that the mere mechanical injury which they may inflict, and the consequent chances of secondary infection, justify, in part, their bad reputation. In addition to the injury from their bite, it is claimed that the body hairs of several of the South American species are readily detached and are urticating.

Recently, Phisalix (1912) has made a study of the physiological effects of the venom of two Avicularoidea, Phormictopus carcerides Pocock, from Haiti and Cteniza sauvagei Rossi, from Corsica. The glands were removed aseptically and ground up with fine, sterilized sand in distilled water. The resultant liquid was somewhat viscid, colorless, and feebly alkaline. Injected into sparrows and mice the extract of Phormictopus proved very actively poisonous, that from a single spider being sufficient to kill ten sparrows or twenty mice. It manifested itself first and, above all, as a narcotic, slightly lowering the temperature and paralyzing the respiration. Muscular and cardiac weakening, loss of general sensibility, and the disappearance of reflexes did not occur until near the end. The extract from Cteniza was less active and, curiously enough, the comparative effect on sparrows and on mice was just reversed.

Spiders of the Genus Latrodectus.—While most of the popular accounts of evil effects from the bites of spiders will not stand investigation, it is a significant fact that, the world over, the best authenticated records refer to a group of small and comparatively insignificant spiders belonging to the genus Latrodectus, of the family Theridiidæ. The dread "Malmigniatte" of Corsica and South Europe, the "Karakurte" of southeastern Russia, the "Katipo" of New Zealand, the "Mena-vodi" and "Vancoho" of Madagascar, and our own Latrodectus mactans, all belong to this genus, and concerning all of these the most circumstantial accounts of their venomous nature are given. These accounts are not mere fantastic stories by uneducated natives but in many cases are reports from thoroughly trained medical men.

The symptoms produced are general, rather than local. As summarized by Kobert (1901) from a study of twenty-two cases treated in 1888, in the Kherson (Russia) Government Hospital and Berislaw (Kherson) District Hospital the typical case, aside from complications, exhibits the following symptoms. The victim suddenly feels the bite, like the sting of a bee. Swelling of the barely reddened spot seldom follows. The shooting pains, which quickly set in, are not manifested at the point of injury but localized at the joints of the lower limb and in the region of the hip. The severity of the pain forces the victim to the hospital, in spite of the fact that they otherwise have a great abhorrence of it. The patient is unable to reach the hospital afoot, or, at least, not without help, for there is usually inability to walk. The patient, even if he has ridden, reaches the hospital covered with cold sweat and continues to perspire for a considerable period. His expression indicates great suffering. The respiration may be somewhat dyspnœic, and a feeling of oppression in the region of the heart is common. There is great aversion to solid food, but increasing thirst for milk and tea. Retention of urine, and constipation occur. Cathartics and, at night, strong narcotics are desired. Warm baths give great relief. After three days, there is marked improvement and usually the patient is dismissed after the fifth. This summary of symptoms agrees well with other trustworthy records.

It would seem, then, that Riley and Howard (1889), who discussed a number of accounts in the entomological literature, were fully justified in their statement that "It must be admitted that certain spiders of the genus Latrodectus have the power to inflict poisonous bites, which may (probably exceptionally and depending upon exceptional conditions) bring about the death of a human being."

And yet, until recently the evidence bearing on the question has been most conflicting. The eminent arachnologist, Lucas, (1843) states that he himself, had been repeatedly bitten by the Malmigniatte without any bad effects. Dr. Marx, in 1890, gave before the Entomological Society of Washington, an account of a series of experiments to determine whether the bite of Latrodectus mactans is poisonous or not. He described the poison glands as remarkably small[A] and stated that he had introduced the poison in various ways into guinea-pigs and rabbits without obtaining any satisfactory results. Obviously, carefully conducted experiments with the supposed venom were needed and fortunately they have been carried out in the greatest detail by Kobert (1901).

This investigator pointed out that there were two factors which might account for the discrepancies in the earlier experiments. In the first place, the poison of spiders, as of snakes, might be so exhausted after two or three bites that further bites, following directly, might be without visible effect. Secondly, the application of the poison by means of the bite, is exceedingly inexact, since even after the most careful selection of the point of application, the poison might in one instance enter a little vein or lymph vessel, and in another case fail to do so. Besides, there would always remain an incalculable and very large amount externally, in the nonabsorptive epithelium. While all of these factors enter into the question of the effect of the bite in specific instances, they must be as nearly as possible obviated in considering the question of whether the spiders really secrete a venom harmful to man.