During a recent return to southern Arizona, we hunted at night for Hogna carolinensis (Araneae: Lycosidae), the Carolina wolf spider, in Spur Cross Ranch Conservation Area, north of Phoenix.
Spur Cross combines the typical xeric scrublands of the Sonoran Desert with mesic riparian oases and thus fosters a noteworthy amount of biodiversity—including a lot of prey for arachnids. In a typical small patch of ground like this, we could easily find several wolf spiders of differing ages:
Using headlamps to pick up the retroreflective eyeshine of wolf spiders, we located countless specimens of H. carolinensis. The specimen shown below, which I collected in Spur Cross at night and photographed in sunlight the following day, is a mature female. Her body length (excluding the legspan) is over 30 mm.
Indeed, H. carolinensis is the biggest lycosid species in North America. Despite the Carolinian reference in its name, the species occurs throughout the United States. There is a variety of regional color morphs. In the arid southwest, the spiders tend to have the largely pale appearance of the specimens depicted here.
Like other wolf spiders, H. carolinensis is a nomadic hunter that roams the ground in search of prey. The spiders breed in the late summer and autumn. While the males die soon after mating, mated females overwinter and lay their eggs during the following spring or early summer. The females deposit their eggs in a sturdy silken sac that they attach to the spinnerets on the rear of the abdomen and carry with them until hatching occurs. The newly emerged spiderlings clamber onto the female's dorsum and ride with her until they are old enough to disperse and fend for themselves. Females sometimes live for several years.
Lycosid retroreflection, or eyeshine, is worth a mention, as it makes wolf spiders very easy to find at night. All you need to locate them is a headlamp on your forehead. Emanating from close to your eyes, the headlamp's beam reveals tiny, diamond-like points of twinkling light on the ground. Each speck of light is a wolf spider. The phenomenon is made possible by the reflective tapetum (from Latin tapete "carpet") at the back of the distinctive eyes that all wolf spiders have.
At night, the shiny tapetum makes the most of any scanty available light and helps the spiders see the movements of prey, conspecifics, or predators in the dark. The eyes of a wolf spider reflect a headlamp's beam of light in such a way that it travels along the same path back to your eyes, resulting in a clearly visible twinkle.