ENV: On the conversations of science
For the past few months i've been engaged in a casual conversation with Texas Parks and Wildlife Biologists and academics about a curious xeric snail that inhabits much of Texas in various specific forms. It's part of a large group of snails that has held my interest for many years -- snails variously placed in the families Bulimulidae, Rabdotidae or Orthalicidae. This particular discussion dove-tailed with an interest of mine in learning more about predation by Hook-billed Kites (in the US, a highly localized and rare species) and changes in prey preference of a related bird, the Snail Kite of the American tropics (including the glamour subspecies Everglades Kite), that feeds on native Apple Snails (Pomacea paludicola) in Florida but may be physically incapable of handling a recent invasive species of Apple Snail (Pomacea canaliculata).
An email describing a personally-witnessed phenomenon i had skeptically questioned was sent to me a couple of days ago, reigniting this interest. Below i am reprinting a series of these emails (not all of them represented here, and edited for tangentiality, obvious errors and to dispose of chitchat and niceties; i have also edited out specific contact info, but if someone has a direct interest email me and i can put you in contact with the person/s you wish to address).
I also thought the series was most instructive in showing how anecdotal concerns get addressed in a community of folks with varying interests in specific groups --the progression of thinking out loud to field observations to rigid studies. Although my personal impression is that these snails are not in dire straits, it is constructive to actually collect observational data to verify impressions, elsewise lose something before action can be initiated. Since a major proponent of arresting declines is having a firm knowledge base, and a lack of that initial base often hampers recovery efforts, any species that gets a pre-needed dose of study is already in better shape than the average species on the planet.
FYI (notes after the exchange):
The species of Rabdotus involved in these discussions is likely R. alternatus alternatus, though Rabdotus dealbatus dealbatus may also be involved; and the species of Euglandina in South Texas is E. texasiana; although E. rosea has been introduced at Brownsville the extent of its spread, if any, is undocumented. Fullington and Pratt (1974) report as follows about E. texasiana:
My entire range of encounters with E. texasiana are on the trails at Santa Ana National Wildlife Refuge and in my grandmother's garden within spitting distance of Santa Ana (but now razed along with the old farmstead).
Under logs and other cover in Thorn Forest and Tropical Deciduous Forest. In South Texas and Northern Tamaulipas it is found in the dense woodland around resacas (oxbow lakes and abandoned channels) and on floodplains. This resaca woodland is essentially a depauperate Thorn Forest Flora with elements from the deciduous forests to the north. In Texas it has mostly been eliminated by agricultural clearing and the original range of E. texasiana has largely been restricted to the remnant tracts.
Specimens maintained [in] captivity by one of the authors (Pratt) fed on Rabdotus alternatus.
Further research on Hispid Cotton Rats (Sigmodon hispidus) turns up this additional list of documented foodstuffs: insects, prairie voles, young birds, eggs of ground nesting birds, crayfish, animal remains, small vertebrates and mice.
References added after the discussion:
Fullington, R.W., and W.L. Pratt, Jr. 1974. The Aquatic and Land Mollusca of Texas. Dallas Museum of Natural History, Bulletin 1, Part Three.
Metcalf, A.L. and R.A. Smartt. 1997. Land snails of New Mexico. Bulletin of the New Mexico Museum of Natural History and Science, 10: 1-145.
Smith, T.B., and S.A. Temple. 1982a. Feeding Habits and Bill Polymorphism in Hook-billed Kites. Auk 99:197-207.
Smith, T.B., and S.A. Temple. 1982b. Grenada Hook-billed Kites; Recent Status and Life History Notes. Condor 84:131.
Turgeon, D.D., J.F. Quinn, Jr., A.E. Bogan, E.V. Coan, F.G. Hochberg, W.G. Lyons, P.M. Mikkelsen, R.J. Neves, C.F.E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F.G. Thompson, M. Vecchione, and J.D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland: 526 pp.
Feb. 1, 2005
Land snail group,
I received a request for information regarding a perceived die-off of the land snail Rabdotus in the Bentsen State Park area in south Texas. I initially asked . . . if this is an issue along roads or somewhere they might have sprayed pesticides or herbicides. But that doesn't seem to be the case. Does anyone have an opinion on what might cause a population decline in Rabdotus? I suppose it could be just random fluctuation in population numbers but I thought I would see if anyone has comments on possible causes. Thanks.
University of Alabama
Systematics and Biodiversity
Department of Biological Sciences
North American Land Snail Webpage
Bob Howells wrote to you upon my request. The issue down here at Bentsen did not arise from a number of shells found on the forest floor, but because no one has seen any live ones lately. What could have affected them? Areas where a lot of shells are found are away from any trails and roads where pesticides or herbicides might have been sprayed.
World Birding Center
Mission, Texas 78572
I received several emails today regarding a perceived die-off of Rabdotus in the Bentsen State Park area. The questions came from a fellow that The Nature Conservancy sometime hires to handle various projects. He apparently has seen large piles of dead shells the locals attribute to roadrunner predation. He was also told that there have been massive die-offs in recent years. I haven't seen any extensive land snail losses during freshwater mussel work in the area and I have always considered Rabdotus to simply be a critter that leaves a lot of dead shells laying around the countryside. Got any thoughts on all of this?
Texas Parks & Wildlife Department
Heart of the Hills Fisheries Research Station
Sent: Wednesday, February 02, 2005 10:55 AM
Subject: Rabdotus declines possibilities
There have been several responses to Mr. Patrikeev's question about Rabdotus. My initial response, was that Rabdotus is a large obvious snail that leaves big white obvious shells. So it may seem that there have been lots dying but in an arid climate the shells stick around for quite a while. But without doing the work to obtain current population estimates and tracking them for a while I don't think we can say if Rabdotus populations in the park are stable or not. Tim Pearce and Jody Thompson also contributed some thoughts and Tony G sent a long email with some good suggestions from someone who is very familiar with the South Texas fauna.
I just have guesses. One guess is that it might have been a freak weather fluctuation that did them all in at the same time. For example, if the weather were moist and they were all out dancing or mating, and then suddenly a hot dry sun appeared, they could have all dried up before finding shelter. Another possibility is a predator or disease that suddenly appeared. It could be a naturally occurring disease or predator, which would not be cause for alarm, or it could be an invasive, such as a flatworm or an insect or something, in which it would be cause for alarm.
I'm curious to know what other people guess.
Timothy A. Pearce
Assistant Curator of Molluscs
Carnegie Museum of Natural History
How long has this decline been going on? I'd be interested in knowing the level of urbanization around the park and densities of invasive flora and fauna (mainly predators of invertebrates) whose effects could have reached a critical point for Rabdotus. I'm just brainstorming out loud of course. Here in Auburn, one of our professors has noticed a substantial decline in populations of large terrestrial gastropods (Euglandina and Limax) since the 70's. He speculated that it might be caused from the increased use of pesticides by homeowners in the 70's and/or predation by armadillos.
I have been mapping Rabdotus for about thirty years and spent lots of time the last two years focusing on them and other genera in the Bulimulidae/Orthalicidae/Rabdotidae. . .
There are a number of things at work with all the species of this genus that may play a part here.
First, they are notoriously localized -- some places may have many thousands, and a mile down the road may have zero in what appear to be identical habitat situations. This has been a known thing for at least 30 years, probably longer (see Cheatum, Fullington, Pratt, Dallas Museum Natural History).
Second, they aestivate perhaps 95% or more of the time in arid south Texas, burrowing under mesquite bark, and deep in the interior of large prickly pear clumps and piles of debris -- in other areas Agarita seems to be a preferred roosting spot. Only in wet weather do they emerge, mate, feed, and return to aestivation as the area dries. Rainy seasons then may net many more "observations," and if someone is out while it's dry it may appear that they have largely vanished. "Piles" of "shells" beneath prickly pears may not all be dead and may be the result of disturbances -- i have long theorized that Hispid Cotton Rats (Sigmodon hispidus) and packrats (Neotoma sp.) may feed on them, and horde them in their nests. I have opened quite a few middens and found them.
Middens of course are a favorite site for locating the native shells of a region and have much bio-archaeological value for that reason. What i don't know is if the rats are just obsessively collecting shells or if they are actually consuming them -- most found shells in middens are whole.
Third, i think die-offs are quite possible in unfortuitous circumstances, and the valley would be a prime location for such recently (if recently dead shells are being used as evidence) -- i don't know that this happened, BUT in a situation where warm rains precede the advance of a strong cold front as may have happened recently in the big snowfall, i suspect that many might be stirred to action only to be caught out in a freeze (pure speculation on my part -- they survive freezes well in more northern areas, but neither are they active in winter).
I have twice been out in heavy, cool, rains and found gazillions of squished Rabdotus on highways (Zavala County and Kerr County). So slick are the roads from snail guts that it is slippery when walking.
Fourth, i've never encountered what i thought were piles that might be evidence of Roadrunner predation. I would like to see such if someone thinks that's what they have (it's just unlikely that, if Roadrunners are eating them, that they're doing so at a "traditional" spot).
. . . One known predator for Rabdotus in south Texas is the Hook-billed Kite (quite rare in Texas, first noted in 1964 i think), which feeds almost exclusively on these critters (and i am actively in pursuit of a pile of shells that remain from such predation for study of some other things i'm looking at). Oddly, the Snail Kite records from Texas (a couple) are of birds that fed largely on crayfish. Hook-billed Kite is a localized species perhaps in response to snail abundance, though it obviously feeds on other species/genera (and arthropods) in parts of its range where Rabdotus does not occur. In Texas there may be perhaps a dozen resident birds (?) and the population is centered around Bentsen SP. I personally would have severe questions if someone were to suggest that Hook-bills might be responsible for a decline. The kites are also restricted (now anyway) to the Rio Grande woodlands, and desert like areas just a few miles north have large, healthy populations of Rabdotus that are likely unpreyed upon, at least by kites.
Fifth, the last predators i can think of off the top of my head would be the predatory snails of the genus Euglandina, and possibly there is contact with the introduced predator Rumina decollata -- but neither of these are in such abundance as to create population slumps IMHO. Euglandina is in fact quite rare in the valley, and while Rumina can be quite common it is usually so only in mesic habitats and urban plantings where it likely seldom contacts Rabdotus.
Lastly, while i wouldn't raise any alarms, and pesticide use is a real possibility, i would say the highly agricultural LRGValley has played a bigger part in any loss of critters by the complete and absolute stripping of vast acreages of land for vegetable farming, all of it now unsuitable for any molluscs. However, i grew up in McAllen and Pharr, a few miles from Bentsen and can tell you that that land was mostly stripped decades ago (in fact, i come from a farming family and we probably bear much of the responsibility for that clearing), so a recent dieoff for that reason would be pretty untenable i would think.
As per my neighbor Bob Howells, i think he's exactly right -- there can be thousands of shells just lying around -- they can be prolific critters (as one can see during a rainy spell) and when they die, they leave behind a fairly heavy and large shell. That shell has helped protect them from dessication during long dry spells (sometimes years), and is heavy enough to resist weathering and decay for many years and thus many generations. And when you're amongst them, they're so dang white you can't hardly miss them.
For that reason (persistence and obvious color) it can be easy (despite their abundance) to overestimate how common they should be, and dang hard to find a live one when they're not moving (unless you like crawling into the middle of prickly pear patches).
So, while it would never be judicious to blow off a concern about declines in any species, just keep in mind that there are numerous factors that may obscure what's really going on in this group.
For expertise on the kites, and probably some good opinion on the relationship, the person concerned might contact John Arvin who works at the World Birding Center at Bentsen -- my opinion, he knows the kites better than anyone, period.
There's probably more i could say, but if so it's not coming to me right now. Feel free to pass this around though.
gulf coast laboratory for wildlife research
hunt, tx, usa
Sent: Wednesday, February 02, 2005 2:20 PM
Subject: RE: Rabdotus declines possibilities
Here's my take, from a non-snail specialist...
For the genus, Neck only lists Rabdotus pilsbryi as restricted or declining in Texas. R. pilsbryi is listed as occurring in Brewster and Terrell Cos in Texas. All five Rabdotus spp. listed in the NatureServe are G5.
Neck, R.W. 1984. Restricted and declining nonmarine mollusks of Texas.
Texas Parks and Wildlife Department, Technical Series 34, Austin. 17 pp.
I doubt that pesticides are causing a decline. The snails obviously made it through the DDT era, though the 1996 RGV Boll Weevil eradication program may have knocked them back...
That program proved disastrous in the RGV due to secondary pest outbreaks, but it looks like they may try it again:
A live population could be monitored through any spraying period to see if there's any mortality... If Tony is correct that they aestivate 95% of the time or more, it seems like the LD50 would have to be very high... This could be tested fairly easily.
I don't think freezes are causing excess mortality given how far north congeners live.
I would be surprised if the packrats are causing excess mortality. Packrats typically build their middens in the middle of large Opuntia plants and feed on the cactus at night. If these snails were common prey for the rats, I would think they'd find somewhere else to aestivate than
Given the Snail Kite's dependence on snails, perhaps the WBC could get some money to study the situation.
Final thought, Joe Ideker should have compiled extensive notes on Rabdotus in the RGV. Christina or Dick Heller should have access to Joe's notes.
Valley Land Fund Photo Contest 2000
Category: All Other Arthropods & Snails
Title: Rabdotus Land Snail
Texas Parks & Wildlife Department
Subject: RE: Rabdotus declines possibilities
Date: Wed, 2 Feb 2005 15:40:25 -0600
. . . thank you very much for replying to my query.
First, I want to clarify few things. First of all, the kites concerned are Hook-billed Kites, and it was John Arvin (ex-WBC biologist) who suggested that these kites may be responsible for the decline.
As for myself, I arrived in Bentsen SP only 2.5 weeks ago, but was puzzled by what was said to me about the snails.
Normally, no predator drives its prey species to extinction. It also appears that no one in the park (including John Arvin) has seen live snails for quite a while.
It was quite humid in the park in the last 10 days or so with periods of drizzle almost daily. The temperature remained c. +10 to 18C during the day, so it was not that cold.
I have not seen any snails aestivating on prickly pear or other [plants] since arrival. There were certainly none on the roads although usually I'd expect to see snails in this kind of weather.
Agicultural lands are adjacent to Bentsen from the north, but two FWS tracts abut the park on the west and east sides.
As far as I know, no parasite/disease studies have been done at Bentsen SP. Hispid Cotton Rats are very common at Bentsen right now, especially in thickets of introduced guinea grass.
Piles of shells [were] attributed to roadrunner predation by John Arvin and park interpreters.
I'll be on the lookout for piles of shells left by Hook-billed Kite (providing that there are any snails left in the park), but see also Smith and Temple 1982 paper.
I'll appreciate further insight from all of you.
I do not [know] of any studies on pesticide drift causing snail mortality, although it is an interesting issue. Most of the remaining native Hawaiian snail populations are in relatively remote areas away from urbanization and agriculture. The mark-recapture methods can be used to estimate disperal rates and distance. The sampled area should be subdivided into quads and each quad should use a unique mark. It is best to give each snail having a unique mark (A123 = quad A, snail 123). Look in "Investigating Animal Abundance: capture-recapture for biologists" by Michael Begon, 1979 University Park Press, Baltimore. The section on partitioning loss and gain discusses the movement of individuals between quads. This is also a very good, hands-on reference for actually doing the mark-recapture studies.
Stephen E. Miller Ph.D.
Ecosystem Conservation Coordinator
U.S. Fish and Wildlife Service
Pacific Islands Office
Honolulu, Hawaii 96850
Sent: Friday, February 04, 2005 2:44 AM
Subject: RE: Rabdotus declines possibilities
Just a handful more notes. First, lest i came across wrong-headed before, my interest in Rabdotus is taxonomic/systematic. My range of experience comes from some rather intense searches for colonies across Texas and adjacent states. The behavioral/ecological observations i made were incidental to the other work, although they of course bear some import on the questions which i am examining.
. . . I too, as [Michael Patrikeev] posited, would be surprised at a decline caused by the kites, except for a couple of ideas, one of which i consider somewhat semantic -- the kites i suspect frequent areas where they have encountered snails and may prey upon them until such time as the effort expended finding the remaining individuals exceeds their individual energy requirements whereupon continued searching becomes counterproductive. Then the birds would move on in search of a richer source which would become food central until the same thing occured (and of course they might frequent multiple sites daily -- they are somewhat clockwork-like in their departure times and pathways which makes it fairly easy for birders to see them). This localized "decline" it would seem to me would constitute something of a cycle for the snails, which should rebound from those that remain. And then, when they have recovered might become a food source for the kites all over again.
Secondly, and John would be a better source here, but i have been under the impression that these kites are "resorting" to Rabdotus at the fringe of their range and that they may be a marginal food source, perhaps less often taken elsewhere. Is this true, and if so, what are they primarily feeding on in other areas?
The packrat midden thing is, i think, as i [implied] before, possibly just hording of shells by the rats. I say this again, based on my experience of finding mostly intact shells in middens.
And finally, i am more intrigued by the Roadrunner thing. And this is possibly a semantic misunderstanding on my part, or else i'm not giving the critters enough credit. The evidence was described as "piles of shells" which i just envisioned as the whole shell. Are these piles of pieces, or are the roadrunners grabbing these things and getting a hold of the foot before then can retract? Roadrunners have a less specialized bill for this purpose and i guess i just imagined that they'd have to break shells to get the booger out.
I might speculate, since i don't know otherwise of roadrunners eating Rabdotus (though i can't imagine why they wouldn't), that if it's a localized behavior, they also might impact the population to some extent. Since i don't see Roadrunners as specialized predators of Rabdotus though, it seems that it would be an opportunistic strategy, and probably not of huge impact. And even if large numbers were taken, you have that old effort vs. reward counterproductivity thing again.
Feb. 4, 2005
Some new information and clarification.
This afternoon (February 4, 2005), we briefly visited the Chihuahua Woods Preserve (Nature Conservancy of Texas), a 400 acre preserve only 3-4 miles from Bentsen SP. Live (aestivating) Rabdotus were easily seen in many Opuntia cactus, other trees and shrubs. They were very obvious and we did not have to look for them. Number of shells also littered the ground under the cacti. However, Lisa Williams (TNC Tamaulipan Thornscrub project director) noted that there were fewer Rabdotus in Chihuahua Woods in recent years than she saw in this preserve previously. I'm adding Lisa to this posting as she's also very interested to know what's happening to land snails in these parts.
Clarification concerning the roadrunners. All shells collected from the "roadrunner feeding stations" were smashed or otherwise broken into. The Hook-billed Kite actually enlarges the aperture leaving the rest of the shell intact. Lisa reported seeing Hook-billed Kites feeding in Chihuahua Woods in previous years, yet Rabdotus [did not disappear] altogether from the preserve.
February 7, 2005 - 10:42 am
Your specimens arrived and they are indeed Rabdotus. I will either need to get some other input from others or check them against my material at home before deciding on a species name, however.
Is this species declining? I don't know. It leaves so many dead shells laying around under normal conditions, that it can be hard to be certain. Unfortunately, I will bet there is absolutely no prior information on abundance or density in the Betsen area, or probably anywhere else in Texas. If indeed there is a real concern about this species being in decline, then it would be wise for someone to start recording abundance and density at several sites in the area (and ideally, in other areas as well). If there is a problem, these data would help confirm it in the years ahead.
I would suspect that hook-billed kites are probably not common enough to drive any snail into decline (good predators don't normally eliminate their prey). But, the road runners may deserve consideration. With pesticides, fire ants, urbanization, and other factors reducing snakes, lizards, other ground nesting animals, etc., is it possible roadrunners may be directing an unusually heavy amount of attention to Rabdotus as these other food sources decline?....just a fisheries guy thinking out loud.
Feb. 7, 2005
I'm glad you've received the specimens.
No live snails of this species have been found in Bentsen SP for some time. [They] are still in Chihuahua Woods (a TNC preserve in Hidalgo County ten minutes from Bentsen), and I'll check on them in Santa Ana NWR over the next few days. We'll also be getting some warm rains this week, so if the Rabdotus won't show up then we can probably talk about a local extirpation.
Recording abundance and density of land/tree snails will likely need an institutional partner as it will require surveys not only at Bentsen, but also in the adjacent areas.
Piles of broken shells at roadrunner favorite feeding sites throughout the park probably indicates that the roadrunners were taking a considerable number of snails (perhaps over a period of time). But as in the case with Hook-billed Kites, I'd imagine that roadrunner predation likely occurred for [a] long time and is not the cause behind the decline. There is no information [on] reptile/amphibian trends in Bentsen SP, and we do not have imported fire ants.
Any anecdotal observations on snake populations at Bentsen? I know that Santa Ana NWR has a healthy population of Indigo Snakes and I believe a healthy pop. of Rabdotus. I suspect that Bentsen's smaller (size ~580 acres vs. SANWR 2008 acres) plus BRGVSP's *much* higher visitation (~400,000 annually vs. ~90,000) has caused a decline in the snake population at Bentsen. If pack rats are eating the snails as Tony suspects and Steven suggests, then this might be part of the decline (if any) as well... i.e. snakes down, rats up, snails down...
Some further clarifications of some questions and suggestions posted.
The Birds of North America "Greater Roadrunner" account written by J.M. Hughes (1996) does not list snails as a food item for the roadrunner. Instead Ms. Hughes wrote "Unusual food items included introduced European snail (Helix pomatia)..." etc. Perhaps, Bentsen SP roadrunners . . . have developed a very particular taste for snails. Although I should say that the Birds of North America species accounts are sometimes not comprehensive and very well written. I'm sure I've heard of roadrunners feeding on snails and saw photos of roadrunners with a shell in its beak from elsewhere.
In relation to Mike Quinn's question about snake decline. We have no data on snake trends, but since park was closed to private traffic road mortality will no longer be an issue. We have anecdotal reports of c. 10-12 snake species, but no inventory was ever carried out.
And finally on rat predation. According to "The Mammals of Texas" (Davis and Schmidly, on-line edition) diet of both Hispid Cotton Rats and Southern Plains Wood-Rat include vegetable matter with bird eggs eaten occasionally. Thus, unless hispid and wood-rats down here also developed unusual tastes, they probably should be excluded as possible culprits. The rats in Hawaii that do eat native snails are omnivorous Old World "Rattus" species: Norway Rat, Roof Rat and likely Polynesian Rat.
I went to Santa Ana National Wildlife Refuge (c. 20 miles from Bentsen SP, but also in Hidalgo County) on Wednesday (my day off). The refuge is c. 5 times greater than Bentsen and has a variety of habitats. Nonetheless, I had no trouble finding live Rabdotus throughout drier sections of the refuge albeit in very small numbers. They were seen aestivating in shrubs (mesquite, [Retama], etc.) in groups of 2-3, although none were seen in prickly pears or other cactus. There were [a] number of empty shells on the ground also, but not as many as in Bentsen. I came across several small groups of shells that also may suggest predation by a roadrunner or other animal. Overall, it appears that the species is more scarce in Santa Ana than it was once at Bentsen, yet live Rabdotus are still found there.
February 10, 2005 - 09:50 am
If you want to clearly demonstrate that there really is a decline ongoing with Rabdotus, you need to start counting snails. Even timed searches would be something (e.g., number of living snails and dead shell found per 30 minutes, etc.) . . . and then write those counts down. Perhaps some of the TPWD "Watch" program volunteers could be drafted to help. So far there is only speculation. Get some hard numbers.
Also, I just remembered, some months back, I was contacted by a John Wise (CMNH malacologist) about directions to locations where a fellow from the Smithsonian could collect Rabdotus. I sent him to the Alice area were there used to be a major concentration. I heard nothing further about it, so assume there was nothing significant to report. I can check to see how that collecting trip came out.
Feb. 10, 2005
I suppose that we may be able to round up some volunteers to do searches along trails and roads in Bentsen during "cooler" months, but I'm not so sure about spring-summer. I guess those counts will need to be compared to other sites, e.g., the TNC preserve, Santa Ana, etc. I've not been here long enough to know how to get involved/organize a project involving multiple partners. I'll make some inquiries though.
Feb. 14, 2005
You might be interested to learn [that] I found TWO live (aestivating) Rabdotus during a time constrained search (1 hour) of vegetation adjacent to Rio Grande trail in Bentsen State Park. Both snails were in the same brazil. None were in prickly pear (very common along that trail) or elsewhere. I'll try to do this survey once a month, but it does not seem likely that many snails will be found there. Habitat: typical Tamaulipan Thornscrub/mesquital.
Sent: Thu 5/5/2005 4:46 PM
From: James Booker
Subject: FW: Rabdotus declines possibilities
I have personally observed roadrunners bringing snails to a favored rock where they smash the snails. The roadrunners leave piles of the broken shells around the rock. This behavior was noted approx. 8 miles north of La Joya, about twenty miles northwest of Bentsen.