Tarantula survey results
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!
The map below 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.
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.
March 14, 2004 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, 2004 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.
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.