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Arkansas Tarantula Survey
Results
Adult male tarantula from Scott County (Kory Roberts)
In March 2004, the ANHC launched the Arkansas Tarantula Survey to map the distribution of tarantulas across the state. Observers of all ages participated in the survey, submitting their tarantula observations through the online database, e-mail, telephone, and U.S. mail.
Each observation gathered by the survey represents an important piece of a puzzle. We now have a much better idea of where tarantulas occur in Arkansas and when they are active during the year. The data provided by tarantula-watchers even provides new information that contradicts some long held views of tarantula life.
With any citizen-science survey there is bound to be bias towards observations from populated areas and such is the case here. Most of the tarantula observations the survey received originated from within or near cities/towns. A more populated locale will inevitably provide a larger pool of participants than an area with a smaller, widely dispersed population. Consequently, lack of observations should not be interpreted as a complete absence of tarantulas from a particular location. That does not lessen the validity of these results, however. This survey was intended to provide a broad-based view of distribution patterns and that is what it accomplished. In fact, survey results now can provide a starting point for more intensive, on-the-ground survey efforts if need be. Now, to the results!
Distribution of Tarantulas in Arkansas
(view larger)The map at right depicts the distribution of tarantulas across Arkansas. Red dots on the map may represent multiple observations. For example, over 70 observations came from Little Rock, but that city is only represented by a single dot. The different colors on the map represent the natural divisions of Arkansas.
The most obvious feature on the map is the lack of tarantula observations from the Mississippi Alluvial Plain (MAP) of eastern Arkansas. The perceived absence of tarantulas from this part of the state is probably the result of a number of factors. Firstly, large areas of the MAP are characterized by low relief and frequent flooding. Tarantulas are animals of dry, upland areas and are not typically found in areas where the ground is saturated for long periods. Consequently, large areas within the MAP simply will not support tarantula populations. Secondly, while drier uplands can be found in the MAP, these lands have mostly been converted over to agricultural production. Not tarantula-friendly habitat, either. Thirdly, certain areas of the MAP are just not that populated, so the number of participating observers might have been too low to detect tarantulas.
A small number of observations were submitted from along Crowley's Ridge. Crowley's Ridge is an anomaly in the flatlands of the MAP. Composed of wind-blown sediment, the ridge is a small upland that rises about 200 feet above the surrounding landscape. Due to its higher elevation, the ridge is not as prone to prolonged periods of standing water. Dry sites on Crowley's Ridge probably provide suitable tarantula habitat. The presence of tarantulas here suggests that populations of these spiders might have once existed (or still exist) in portions of Lawrence, Jackson, and Woodruff Counties between the eastern edge of the Ozark Mountains and Crowley's Ridge.
Limestone glade in the Ozarks
In terms of the rest of Arkansas, the Ozark Mountains, Arkansas Valley, and Ouachita Mountains yielded the most tarantula observations. These regions of Arkansas support a number of habitats amenable to the needs of tarantulas from open, rocky glades to dry forests. The fact that a number of larger cities are located within this region also helped boost numbers of observations as well. The West Gulf Coastal Plain, while containing habitats that could support tarantulas, contained a smaller number of observations. Again, lack of observers in certain areas could have played a role here.
Tarantula Activity during the Year
(view larger)March 14 marked the first observation of tarantulas during the survey period. Dr. William J. Baerg reported tarantulas unplugging their burrows in northwestern Arkansas as early as mid-February. At this time of year, temperatures are relatively cool and on warm days tarantulas will spend time at the entrance of their burrow warming themselves.
Number of observed tarantulas increased dramatically in May. From March to May, many of the tarantulas reported to the survey were adult males. Adult males were reported moving across roads, in driveways, and under pool covers. Male tarantulas in Arkansas generally reach sexual maturity in the late summer/early fall, mate, and die with the coming winter. Obviously, the results of the survey indicate that a number of adult males are able to survive over the winter into the following spring. Baerg thought that adult males that did survive into the next year might mate but may not produce viable young or live past July.
Immature female tarantula from Conway (Amy Blaylock)
In addition to adult males, a number of immature tarantulas were reported in transit during the spring. A widespread assumption is that immature and adult female tarantulas do not disperse. Immature tarantulas were observed by a number of survey participants walking across roads and through lawns. Why these immature were dispersing is not clear. In one location, four immatures were collected by a family in western Pulaski County. All four tarantulas were of the same size (probably same age as well) and were captured over a matter of days in the same vicinity. These observations of immatures dispersing is a novel find from the survey and opens up a number of questions regarding the life of immature tarantulas.
We learned a great deal about tarantulas in Arkansas thanks to all the tarantula-watchers that diligently submitted their observations. The results presented thus far are just a small part of what we have learned. A more detailed report on the survey results is being prepared for submission to a scientific journal. Once that paper is completed, it will be posted to the results section. Check back for updates.
What's Next
Now that we have a better idea of where tarantulas occur in Arkansas, we really need to determine what species we have in the state. All tarantulas in the United States belong to the genus Aphonopelma. Over 50 species of Aphonopelma have been described from the United States alone. The taxonomic status of several of these species is highly questionable as most Aphonopelma species were described from only one to two specimens. Such a limited sample size does not take into account individual or regional variation.
Aphonoplema baergi from Fayetteville (William J. Baerg)
Three tarantula species have been described as occurring in Arkansas. Aphonopelma hentzi was the first tarantula species (1852) described from the U.S. and has been said to occur in Arkansas. That species was stated as being the only one occurring in Arkansas during the survey. The reason being that the taxonomic validity of the other two species is very much in question. One of those two is Aphonopelma baergi, named after Dr. Baerg. Aphonopelma baergi was described in 1940 from two specimens collected (purportedly) from Fayetteville, Arkansas. In 1995, A. odelli was described as occurring in "western and central Arkansas." Whether any or all of these species actually occur in Arkansas is uncertain as A. hentzi has never been formally documented in Arkansas, A. baergi may have been described from specimens actually collected in Mexico/Central America, and label data for Arkansas specimens of A. odelli do not match the species described distribution.
Not knowing what tarantula species actually occur here can have a real impact on conservation of these species. Arkansas may only have one broadly distributed species or we could have several geographically isolated species across the state. Right now, that information simply does not exist. Such information will ultimately dictate whether these spiders require special conservation efforts.
The Arkansas Tarantula Survey provided distributional data on tarantulas across the state. It also resulted in the acquisition of several live and dead specimens. The collected specimens are now the target of research geared toward defining the taxonomic status of tarantulas in Arkansas. This research will consist of precise morphological measurements and the examination of genetic variation among specimens.
