cphoenix@csli.Stanford.EDU (Chris Phoenix) (05/26/91)
I read recently on some group (maybe this one?) that there is a recently- appeared type of fly that lays eggs in living tissue, and the maggots eat the tissue, with often-fatal results. Apparently it's enough of a threat that there's an international effort to wipe out the flies before they spread. It seems like such a fly would have to arise from two mutations/changes at once: First, to lay its eggs in living rather than dead tissue; second, to have its maggots able to eat living tissue. I've just had confirmation that maggots are sometimes used to clean wounds, so it appears that with "normal" flies, they are not a danger. As far as I know, "normal" flies also do not lay eggs in living tissue either. (Though I don't know that much...) So we have two behaviors/capabilities, one of which most (or all) flies don't do, and one of which would cause a waste of the fly's resources. And yet we have this fly that has learned to do both, probably within a short time frame, and seems to be successful at it. From what I know of evolution and natural selection, this doesn't make sense. 1) Flies have pretty short generations, which means they've had a lot of time to optimize. Why should they suddenly change? 2) How could a fly learn two behaviors at once, neither of which appears useful by itself? Now that I think of it, the original post mentioned that cow's vulvas are one of the target areas of the new fly. I suppose laying eggs there could be useful even without the ability to eat the cow if the maggots could hitch a ride as the cow defecated. Does anyone know if this happens? I apologize if this post is too gruesome... -- Chris Phoenix cphoenix@csli.stanford.edu #insert <funnyquote.h> #insert <graphic.h> #insert <stddisclaimer.h>
andrewt@cs.su.oz (Andrew Taylor) (05/26/91)
In article <19490@csli.Stanford.EDU> cphoenix@csli.Stanford.EDU (Chris Phoenix) writes: > I read recently on some group (maybe this one?) that there is a recently- > appeared type of fly that lays eggs in living tissue, and the maggots eat > the tissue, with often-fatal results. ... The larva of a number of fly species are occasionally found in humans. I guess many more occur in other animals. One that does afflict humans regularly is the Tumbu fly (Cordtlobia anthropophaga) of West/Central Africa. It lays its eggs on clothing. The larva hatch in response to body warmth and invade the skin. Two weeks later they emerge, fall to the ground and pupate. They develop into adult flies in several days. Tumbu fly larvae can be removed by covering the larvae's entrance hole with oil. The larvae will partly emerge to breath and it can be extracted. I've never heard of a fly whose is larvae has fatal effects on humans. Andrew Taylor
isaak@imagen.com (mark isaak) (05/27/91)
In article <19490@csli.Stanford.EDU> cphoenix@csli.Stanford.EDU (Chris Phoenix) writes: >I read recently on some group (maybe this one?) that there is a recently- >appeared type of fly that lays eggs in living tissue, and the maggots eat >the tissue, with often-fatal results. Apparently it's enough of a threat >that there's an international effort to wipe out the flies before they >spread. This sounds like the screwworm fly, native to Mexico/southern USA. It lays eggs in open wounds, and the larvae feed on the living tissue. It used to be the bane of cattle ranchers, who would lose thousands of head a year to them, and it killed a dozen or so people per year, too. Some time ago (1960's?), it was eradicated in some areas and brought under control in others by using the biological control measure of releasing sterile males. I believe there are some joint US-Mexico plans to try to eradicate them completely by extending this treatment further and further south. The flies are not new. What's new is that they have now been accidentally imported to Africa (Lybia, if I remember right), where they threaten humans, livestock, and native mammals alike. That's probably the focus of the international effort you heard about. -- Mark Isaak imagen!isaak@decwrl.dec.com or {decwrl,sun}!imagen!isaak "Convictions are more dangerous enemies of truth than lies." - Nietzsche
callahan@cs.jhu.edu (Paul Callahan) (05/27/91)
In article <1991May27.020638.27148@imagen.com> isaak@imagen.com (mark isaak) writes: >In article <19490@csli.Stanford.EDU> cphoenix@csli.Stanford.EDU (Chris Phoenix) writes: >>I read recently on some group (maybe this one?) that there is a recently- >>appeared type of fly that lays eggs in living tissue, and the maggots eat >>the tissue, with often-fatal results. Apparently it's enough of a threat >>that there's an international effort to wipe out the flies before they >>spread. > >This sounds like the screwworm fly, native to Mexico/southern USA. . . . >That's probably the focus of the international effort you heard >about. If "wipe out" means what it sounds like, isn't there a significant ethical issue involved? I'm not convinced people have the right to cause the extinction of a species even if it sometimes threatens human life. What are the mitigating circumstances? The fact that it's a recent mutation? The fact that it's "just" an insect? I may be misinterpreting the issue. If the attempt to eliminate these flies turns out to be successful, will the program be carried out till it is complete, or will some small population be kept in quarantine? Maybe no effort to reduce insect populations has ever been successful enough to need to worry about this issue. Even so, I consider it important to work out all foreseeable contingencies before embarking on such a program. -- Paul Callahan callahan@cs.jhu.edu
arromdee@cs.jhu.edu (Kenneth Arromdee) (05/27/91)
In article <callahan.675353595@newton.cs.jhu.edu> callahan@cs.jhu.edu (Paul Callahan) writes: >If "wipe out" means what it sounds like, isn't there a significant ethical >issue involved? I'm not convinced people have the right to cause the >extinction of a species even if it sometimes threatens human life. I think we already handled these issues when smallpox was eradicated. -- "Let's see your power stop me now, Deus ex Machina Man!" [safe falls on villain] "Not bad...." Kenneth Arromdee (UUCP: ....!jhunix!arromdee; BITNET: arromdee@jhuvm; INTERNET: arromdee@cs.jhu.edu)
callahan@cs.jhu.edu (Paul Callahan) (05/27/91)
In article <10801@emanon.cs.jhu.edu> arromdee@cs.jhu.edu (Kenneth Arromdee) writes: >I think we already handled these issues when smallpox was eradicated. [Disclaimer: This is utterly unrelated to my field, so I may say ridiculous things. Commentary from *knowledgeable* sources would be appreciated.] Did we handle the issues, or just sweep them under the rug? This is not a rhetorical question; I want to know. Was an ethical manifesto published simultaneously with the eradication of smallpox? If so, what was the conclusion? In any case, there are fundamental differences. First of all, an insect species can be argued to have more ethical significance than a virus, by virtue of being a much more complex organism. Second, I was under the impression that smallpox was not completely destroyed, and it could be reintroduced if so desired (obviously, it would be undesirable). I don't know how long smallpox can be made to last in a dormant state; it is clear, however, that there is no technology available for preserving screw flies very long in a dormant state. Finally, it would be possible to allow screw flies to live in their natural environment without immediately endangering human life. I'm not sure if this is true for smallpox. Can it infect animals besides humans? If there were some way to perfectly record the DNA sequence of screw flies and the technology existed to reconstruct a living specimen, then I would not have so many qualms about eradicating them. Under the circumstances, however, I believe that it is insufficient to argue that risk to human life always justifies the total destruction of a "lower" life form. -- Paul Callahan callahan@cs.jhu.edu
unasmith@phoenix.Princeton.EDU (Una Smith) (05/28/91)
cphoenix@csli.Stanford.EDU (Chris Phoenix) writes: >>>I read recently on some group (maybe this one?) that there is a recently- >>>appeared type of fly that lays eggs in living tissue, and the maggots eat >>>the tissue, with often-fatal results. [stuff deleted] isaak@imagen.com (mark isaak) writes: >>This sounds like the screwworm fly, native to Mexico/southern USA. On the topic of gross insect parasites, there are the botflies of Central and South America. The females lay eggs under the exposed, soft skin of particular host species (there is a botfly that prefers humans above all other hosts). The larva develops a barbed tail, much like a harpoon, which it works down through the muscle tissue of the host, and snorkel-like breathing tubes which it extrudes through the entrance hole in the host's skin. They don't crawl around; I believe that they absorb nutrients through their skin. As larvae, they excrete antibiotics, but once they pupate, infection sets in and the local swelling forces the pupa out through the entrance hole. Infestation does not ordinarily cause death, although it may contribute to the ill-health of a host. Dr. Katie Milton, a primatologist, believes that due to the decline of many primate species in the neotropics, botfly species that commonly infest various monkeys are being forced to switch to human hosts (and, lucky for them, there are lots of human hosts around, since humans are directly replacing the monkeys). callahan@cs.jhu.edu (Paul Callahan) writes: >If "wipe out" means what it sounds like, isn't there a significant ethical >issue involved? I'm not convinced people have the right to cause the >extinction of a species even if it sometimes threatens human life. Well, then, would you prefer that small pox be allowed to persist somewhere in the world? Don't worry too much; "eradication" refers to eliminating the parasite in domestic animals only. There is very little concern about the effects of the parasite on wild "reservoir" species, except among conservationists. Perhaps it would also make you feel better to keep in mind that the activities of human beings has led to the introduction of a foreign species to a new environment; neither host nor parasite is entirely prepared to deal with the consequences. Under such circumstances, isn't it more OK for human beings to fix the mess they made. True, it's arguable whether it makes any difference that humans introduced an organism to a new environment. >What are the mitigating circumstances? The fact that it's a recent mutation? There's no "mutation" in evidence here. >The fact that it's "just" an insect? Certainly, humans do not hold all other species to be equal. Is this wrong? Is this a habit that we can change? Should we? - Una Smith School of the Environment, Duke University
callahan@cs.jhu.edu (Paul Callahan) (05/28/91)
In article <10091@idunno.Princeton.EDU> unasmith@phoenix.Princeton.EDU (Una Smith) writes: >Well, then, would you prefer that small pox be allowed to persist >somewhere in the world? I'm aware of the eradication of small pox. I had considered mentioning it in my original posting, but I decided it wasn't all that similar. If I had realized that people were going to use it as the definitive counterargument, I would have mentioned it. See my previous posting for related comments. >There's no "mutation" in evidence here. Ok. I wasn't the one who made that claim; I was simply making the assumption that it was true, on the grounds that it would only weaken my argument that there was an ethical question involved. Perhaps the subject line ("Mutant flies") ought to be changed. >Certainly, humans do not hold all other species to be equal. Is this >wrong? Is this a habit that we can change? Should we? Aha! But then a small pox virus isn't equal to a screw fly, is it? I'm perfectly willing to assume the ethical inequality humans > insects > viruses, though I'm not certain of the grounds that I'd use to argue for it. If it were a contest between a human life and a single screw fly, or even a fairly big population of them, I'd side with the human life. When the question is, instead, the extinction of a species, it's not as clear to me. Obviously, I'd rather have the extinction of screw flies than the extinction of humans. However, this does not mean that I would rather have the extinction of screw flies than the loss of a human life. Considering that many species have become extinct as part of the natural evolutionary process, there is no reason to believe that it is the duty of the human race to insure that all current species continue to exist. However, when a decision is made to deliberately cause the extinction of a species (and I'm not implying that such a decision has been made with respect to screw flies), one should explicitly weigh all of the ethical factors involved. What I see is the implicit assumption that a threat to human life and prosperity gives us a carte blanche to ignore all other factors. This assumption disturbs me. With regards to animals, many people have trouble seeing beyond the categories "fuzzy" and "icky." As screw flies clearly fall into the latter category, I imagine few would bemoan their disappearance. If the human race had the power to eradicate a species at will, as may one day be the case, I would argue that every species deserved, at the very least, a fair trial, unbiased by mere sentiment or aesthetic principles. Moreover, if it became technology feasible, I would insist that we had the duty to archive sufficient genetic information to restore any species we destroy, regardless of any commonly held judgment about its significance or beneficial nature. Those are my opinions. I am not so much interested in having others adopt them as in having others admit that there are ethical questions involved, and *clearly define* the principles they are using before going ahead with large-scale irreversible acts. It's easy to dismiss my concerns as mere pedantry or monomania, but as technological power increases, such questions will become very real. -- Paul Callahan callahan@cs.jhu.edu
cl@lgc.com (Cameron Laird) (05/29/91)
In article <1991May27.020638.27148@imagen.com> isaak@imagen.com (mark isaak) writes: . . . >The flies are not new. What's new is that they have now been >accidentally imported to Africa (Lybia, if I remember right), >where they threaten humans, livestock, and native mammals alike. >That's probably the focus of the international effort you heard >about. . . . There're political problems here, to accompany the biologic ones: 1. this is the first time screwworm flies have been observed in Africa; 2. they could be both very destructive and *very* expensive to control in Africa, given various social and ecologic realities; 3. the technologies developed in the eradi- cation in North America can be expected to be quite effective in wiping out the small infestation in Libya; however, 4. the US classifies Libya as an outlaw country, which is not to be helped (ap- proximately). It'll be interesting to learn how this one turns out. -- Cameron Laird +1 713-579-4613 cl@lgc.com (cl%lgc.com@uunet.uu.net) +1 713-996-8546