Dry bite

A dry bite is a bite by a venomous animal in which no venom is released. Dry snake bites are called "Venomous snake bite without envenoming".^[1] Dry bites can occur from all snakes, but their frequency varies from species to species. For example, brown snakes can inflict dry bites 80% of the time while Australian taipans only inflict it 5% of the time.^[2] About 25% of snakebite cases can be dry bites and is characterized by fang and tooth marks and the absence of injected poison.^[3]

Dry bites often are confusing for the attending physician and the victim. The phenomenon also is exploited by quack doctors as evidence for the effectiveness of supposed miracle cures.^[4]

Dry bites from spiders such as tarantulas and large Sparassidae also are common and simply can be ignored or, if appropriate, treated using mild antiseptics.^[5] In practice it is not necessarily simple to tell a dry bite from a dangerously or at least harmfully venomous bite. This is not much of a problem where there is no specific antivenom, because then main options are prevention of infection and reactive treatment of symptoms as they occur; but where one is dealing with say, a black mamba bite, where the venom dosage often is large, the effects are rapid, and an effective antivenom is available, one seldom can afford to delay treatment long enough to confirm whether the bite is dangerous. Also, bites such as those from snakes with venom that cause blood or tissue damage, such as many Viperidae, may take a long time to kill, but do not take long for the tissue damage to become irreparable, possibly leading to the loss of a limb, or worse. Such envenomation should be treated as soon as practical, not only after symptoms become severe.

One of the most difficult problems associated with dry bites, is that it is not simply a matter some bites being dry and others venomous; some species have quite sophisticated mechanisms for controlling the dosage of venom injected, which can vary widely and very unpredictably. Jumping to conclusions on the basis of just a few experiences of a given species or a group of related species, can be fatal. There are many variables; anecdotally, very young venomous snakes for example, tend to have disproportionately dangerous bites—there is reason to suspect that they inflict a full bite routinely.

There is reason to suspect that similar effects occur with spiders. For example, it is a cliche that bites by Sparassidae are largely harmless (see Wikipedia article and associated links) but some reports clearly suggest that some of their bites cause marked neurotoxic effects. For example, in South Africa the common "Rain Spider" Palystes castaneus and similar species, is usually described as negligibly venomous, and certainly it is at the least difficult to find documented cases of serious effects. However, a case in Cape Town is typical of evidence of the dangers of generalising.

In her garden with her bare arm in bushes, a woman felt a sting and withdrew hurriedly. Seeing nothing, she thrust her arm, in again and felt a worse sting; inspection revealed a Palystes nest-cocoon, with the female on guard. There was local redness at the site of the bites, but no other ill effects. Later that evening, however, there was dizziness and nausea, and her arm became swollen and painful, with local discoloration at the sites of the bites. The pain and swelling took several days to subside.^[6]

Given that the typical Palystes bite is less traumatic than a bee sting,^[7] it is altogether plausible that many are dry bites, but as in this case, when there were two bites, possibly less dry than usual, the putative effects make it altogether reasonable to suspect that the venom as such is non-negligible. It is not possible to carry out controlled studies on humans, and the effects on non-human subjects cannot be trusted because there are major unpredictable differences between species in such matters.

See also

• Snakebite
• Spider bite

References

1. ^ Silveira, PV; Nishioka Sde A (1995). "Venomous snake bite without clinical envenoming ('dry-bite'). A neglected problem in Brazil.". Trop Geogr Med. 47 (2): 82–85. PMID 8592769. 
2. ^ Dart, Richard C. (2004). Medical Toxicology. Lippincott Williams & Wilkins. pp. 1551. ISBN 9780781728454. 
3. ^ Thygerson, Alton L.; American College of Emergency Physicians, Emergency Care and Safety Institute (2006). First Aid, CPR, and AED (5th ed.). Jones & Bartlett Publishers. pp. 120. ISBN 9780763742256. 
4. ^ Boos, Hans E. A. (2001). The Snakes of Trinidad and Tobago. Texas A&M University Press. pp. 176. ISBN 9781585441167. http://books.google.com/?id=tItyRBj7-zUC&pg=PA176&dq=dry+bite#PPA176,M1. Retrieved 2009-01-12. 
5. ^ Schultz, Stanley A.; Marguerite J. Schultz (1998). The Tarantula Keeper's Guide. Barron's Educational Series. ISBN 9780764100765. 
6. ^ D'Ewes, Dudley; Wayward naturalist, Chapter 12; Howard Timmins, Cape Town, 1967
7. ^ Skaife, S. H.; A Naturalist Remembers; Pub: Longmans South Africa, 1963