Between August 26 and 28, I was in Portal, south-east Arizona, helping my friend Sarah Supp do rodent censuses. Sarah, who is also a graduate student at USU, is interested in long term metacommunity dynamics at this site. The Portal Project is an interesting long-term study that has been active for about 30 years. Our work in the field consisted in placing Sherman traps baited with millet, and collecting and identifying trapped rodents. It was very hot there but being in the desert was a treat in terms of landscape and biology.

Portal field site

Our kitchen and storage area at the site was a small ramada, which also provided a welcome source of shade. I soon noticed against the ramada walls an abundance of tangle webs that contained conspicuous round, cream-colored egg cases made of silk. These cases were being guarded by relatively large, yet very shy female black widows (family Theridiidae, genus Latrodectus), which I assumed belonged to the species hesperus based on geographic location. Females are a shiny black or dark brown with a typical reddish-orange hourglass on the underside, whereas the much smaller males are brown with whitish markings. A female can produce several egg sacs during her life-time (1 to 2 years), and each sac can contain hundreds of eggs.

Female Latrodectus with three egg cases

Female Latrodectus with a large prey item

A common spider at the field site was the orbweaver Neoscona oaxacensis (family Araneidae). The webs were often built between plants and low on the ground so that it was easy to accidentally run into them. This species, also known as the Western Spotted Orbweaver, has a typical leaf-pattern on the back of the abdomen, and the underside consists of a black cross, with four yellow patches in each corner. Notice also the orange spots near the spinnerets. The sternum is yellow, with thick black edges.

Neoscona oaxacensis

The underside of Neoscona oaxacensis

Neoscona oaxacensis with a prey item

It was interesting to notice how Neoscona appeared to be less often in the web during the hottest part of the day. I found a female resting in the shade of a Soaptree Yucca leaf (Yucca elata) to avoid the desert heat and reduce water loss.

Soaptree Yucca in which I found a Neoscona oaxacensis

N. oaxacensis resting in the shade of a Yucca leaf

While I was recording information on trapped rodents, I noticed a spider wandering on my arm. I placed it on my datasheet and took the picture below. I did not know what this spider was at the time as it did not look familiar. I later found out that this spider belongs to the Diguetidae (genus Diguetia), a very exciting find since I had never seen a member of this family before. Diguetids are six-eyed web spiders that live in New World deserts. Diguetia builds a domed sheet web that is topped by a tubular retreat that has incorporated plant material.

Diguetia on my datasheet

At night, Sarah and I searched for scorpions with a UV light (scorpions fluoresce under UV light). Like spiders, scorpions are arachnids and predators. After a few minutes, we detected a glow that indicated the presence of a scorpion. Upon closer inspection, we realized that the scorpion was holding a much younger scorpion in its left claw. We observed the scene for a while but the large scorpion did not move, probably intimidated by our light. Apparently, scorpions do not hesitate to eat their own kind. The  young scorpion was noticeably darker than its predator. It would be interesting to know if it belonged to a different species.

Scorpion cannibalism (UV light)

Scorpion cannibalism (regular flashlight)

On Saturday, after collecting rodents, we took a break and drove to the Southwestern Research Station (SWRS), a year-round field station located 5 miles from Portal, at an elevation of 5400 feet. The SWRS is under the direction of the American Museum of Natural History and gives scientists the opportunity to do research projects in the Chiricahua Mountains. It was a very nice place, with cabins and even a swimming pool and a volley ball court. I was excited to search for spiders here, as the biota here is composed of a unique mix of desert and mountain organisms, including endemic species.

The Southwestern Research Station

Our first spider was a Wolf Spider with a mottled pattern of white and black spots on a rufous-colored abdomen. This spider was wandering about the leaves and fallen pieces of bark on the ground:

On a nearby fallen branch was a different species of Wolf Spider, belonging to the genus Rabidosa (from the latin rabidus, to rave, and the greek osa, full of). There are only five North American species of Rabidosa, each with typical morphological traits. The carapace of Rabid Wolf Spiders has a pair of dark brown/black longitudinal stripes on a pale background color. The dorsum of the abdomen typically consists of a dark brown median stripe flanked by a lighter color. According to Nearctic species of the genus Rabidosa (Araneae:Lycosidae), the species I photographed corresponds to descriptions of Rabidosa santrita, a species with white chevrons on the posterior half of the abdomen. R. santrita is known from desert riparian habitats of Arizona.

Rabidosa santrita climbing up a branch

The rolled-up tip of a plant revealed a dictynid spider in a messy-looking tangle-web, complete with the usual suspended left-overs from previous meals. What a difference compared to the nicely kept webs of araneid spiders!

Dictynid in her web

Further up the trail I found a plump jumping spider in a wooded area not far from the trail edge. She appeared to be a uniform pale yellowish-orange, with perhaps a few darker areas on the abdomen.

An unidentified jumping spider on a piece of bark

As we walked back to the cabins, we found some Linyphiid spiders not far from a stream. These spiders, which are also known as Sheet Weavers, typically hang upside-down in their webs, which look like a suspended sheet, as seen in the pictures below. I do not know what species this is, but it reminds me of the Bowl and Doily spider (Frontinella communis), which it might be closely related to. The webs I found consisted in a sheet under a tangle-web. The tangle-web portion is not very visible in my pictures.

Linyphiid spider waiting under its sheet web