Pelegrina arizonensis (Peckham and Peckham, 1901)
A Jumping Spider
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Basis for Listing
The Minnesota ocurrences of Pelegrina arizonensis (a species of jumping spider) represent the southeastern limit of the range of this species, which is centered in the prairie provinces of Canada. Most of the documented occurrences in Minnesota are from the east-central to southeastern part of the state; however, there are two northern outliers, one in Polk County and the other in Cook County (Richman and Cutler 1977; Cutler and Jennings 1985; Ehmann and Boyd, 1997; Ehmann et al. 2010). This species of jumping spider has been collected from about 20 sites, predominantly on the Anoka Sand Plain and The Blufflands ecological subsections. Pelegrina arizonensis was listed as a special concern species in Minnesota in 1996.
Jumping spiders are one of the most recognizable types of spider as they generally have a stout body, rather short legs, a very large set of eyes, and the ability to jump. Their body shapes and colors often imitate prey such as ants and beetles. Adult P. arizonensis are usually 4-6 mm (0.16-0.24 in.) long. They have mahogany markings on their heads (cephalothorax), which are most pronounced on males. Their abdomen is brown edged in white, with two wavy white stripes running lengthwise down the middle. The first pair of legs on males is larger than the others. The similar Pelegrina insignis has distinct rows of black spots on a nearly solid brown abdomen. The similar P. proterva has a yellow overall appearance and black abdominal spots that in females are often edged in red.
Cutler (1988) associated P. arizonensis with the seed heads of prairie forbs, especially large-flowered penstemon (Penstemon grandiflorus), round-headed bush clover (Lespedeza capitata), horseweed (Erigeron canadensis), and stiff goldenrod (Solidago rigida). These are plant species common for fire-dependent communities, such as prairies and savannas. Based on sweep net samples, Ehmann and Boyd (1997) and Ehmann (2002) associated P. arizonensis mostly with dry prairie and dry savanna in sandy soil or dunes, several times near moss and once in direct association with gopher mounds. A few specimens have come from bluegrass (Poa pratensis) meadows and more mesic prairie. Specimens collected by Cutler and Jennings (1992) from 1964-1989 all came from sand prairie.
Biology / Life History
Jumping spiders do not spin webs for catching prey. Instead, they use silk to construct small tent-like silken retreats under rocks or logs or on plants. Female P. arizonensis use seed heads and capsules of native forbs as egg-laying sites, and both immatures and adults use these structures as retreats at night and during hibernation. The females also lay their eggs in them. Jumping spiders are most active during the day, and they prefer sunshine. They tend to stay in their retreats on cloudy or rainy days. Jumping spiders are generally interested in whatever approaches them and will often turn and face human observers and may even advance towards them. They are harmless to people.
Jumping spiders have four pairs of eyes with the large principal pair giving them better vision than other spiders. The forward-looking placement of this pair of eyes provides binocular vision enabling them to judge distances accurately; they are able to identify prey, predators, and mates from up to 30 cm (1 ft.) away (Weber 2002). Physiological and behavioral experiments have demonstrated that they have color vision possibly extending into the ultraviolet range.
Jumping spiders feed primarily on insects, though some feed on other spiders. They will even feed on other jumping spiders usually those that are smaller than themselves. Jumping spiders actively stalk their prey instead of snaring it in a web. They may, however, steal insects snared by the webs of other spiders. Jumping spiders hunt primarily during the day using their keen eyesight to find prey. Having spotted their quarry, a jumping spider will slowly stalk the prey until it is within jumping distance. Then it lifts its front legs and pounces. Like all spiders, jumping spiders move their legs not by muscular contractions but by changing the pressure of the fluid within them. This hydraulic system enables them to jump up to several times their body length without having large muscular legs. Before jumping, the spider always affixes a silk safety line to whatever it is jumping from; in case it falls, it can climb back up this tether.
The same visual capabilities that are critical to jumping spiders’ success as hunters also support complex courtship behaviors. Males often differ in appearance from females and may have colorful, sometimes iridescent, modifications to their bodies, front legs, or mouthparts. The parts of the male's body that are used in courtship are often conspicuously colored. In many jumping spider species, the males perform courtship dances that are specific to that species in front of the female. The male's movements range from a slight lifting of a leg to complex movements such as bobbing their bodies, twitching their abdomen, performing zig-zag movements, waving their front legs, or flashing their mouthparts into the eyes of the females. Some male jumping spiders also have auditory signals that, when amplified, sound like buzzes or drum rolls. It is presumed that females choose mates based on the males’ courtship dances. After mating, females lay their eggs in their silken retreat and often guard their eggs and newly hatched young.
Conservation / Management
As with other prairie-dependent arthropods, the survival of P. arizonensis in Minnesota requires the active management of the remnants of its habitat. Periodic wildfire was the primary agent preventing invasion of trees in the pre settlement prairie landscape, and prescribed burning is the standard management tool to achieve this in remnants. Because fire is lethal to the spiders, managers must apply it strategically to avoid extirpations. And because the distance between remnants probably prevents recolonization, these extirpations could accumulate, eventually eliminating the species from the state. Fire management must include division of sites into multiple burn units and rotation of burning among them on a schedule that assures adequate survival of each burn for population recovery and enough time between burns for recovery to occur.
Seed harvesting from prairie remnants to support recreation of prairie habitat is another potential threat that can be ameliorated with a strategic approach. Females of this species spin silken "retreats" in the seed-bearing structures of some prairie forbs, wherein they lay and guard their eggs. Accordingly, removal of these structures for seed harvest should never be total, and the"leave' plants should be widely distributed, not confined to one or a few small stands.
Although remnants of natural areas may often be too small or isolated to maintain populations of some rare verterates, they may be suitable for maintaining invertebrates. Jumping spiders are benign to humans, diverse, colorful, and behaviorally complex, so they may be good ambassadors for their kin and invertebrates in general.
Best Time to Search
The best time to search for P. arizonensis is from June through September. Future surveys may want to employ hand searches and leaf litter collection for sampling, instead of sweep netting.
Conservation Efforts in Minnesota
Pelegrina arizonensis was found in six localities including four new sites in 1996 (Ehmann and Boyd 1997), in three localities including one new site in 2001 (Ehmann 2002), and in seven localities including four new sites in 2008-2009. This suggests that the species may be the most common of Minnesota’s special concern spider species, though more work is needed to verify this. A related species, P. insignis, was nearly an order of magnitude more common during the 1996 study. Several P. arizonensis populations are located on lands managed by public and private conservation organizations including several Scientific and Natural Areas, two Wildlife Management Areas, a State Park, and a National Wildlife Refuge. Conservation efforts would be facilitated by learning more about the species' biology and details of its habitat preferences. Any new records will be of interest.