Argiope Spiders

Late summer/early fall seems to be the season of spiders.  This time of year, it is difficult to walk through the woods, fields, or wetlands without wearing webs on your face and pants.  Some of the most common and conspicuous spiders that I notice this time of year are those in the genus Argiope.  Often called "garden spiders," these ~2" long (the bodies of the males are much smaller) yellow, black, and silvery white orb-weavers can be quite intimidating for those with even the slightest bit of arachnophobia, but unless you have six legs and a pair of antennae, you have nothing to fear.  A severly harassed female with an egg sac may bite a human, but the bite is said to be no worse than a bee sting.

Female Black-and-yellow Argiope.  Be sure to click on this photo to enlarge it so that you can see the characteristic zig-zag stabilimentum that she weaves into her web.

An interesting feature of the argiope spiders is that they weave a ribbon of silk called a stabilimentum into their webs; this stabilimentum is often in a zig-zag pattern.  Although entomologists cannot agree on the true purpose of the stabilimentum, there are several theories as to why argiope spiders expend energy to create them.  One possibility is that it adds to the stability of the web.  Another idea is that the stabilimentum is easily seen by birds and mammals that as a result avoid the web and therefore don't destroy it.  Others think that the structure helps to camouflage the spider, while some think that the stabilimentum may actually attract potential prey.  Regardless of its purpose, each species of argiope spider produces a distinctive stabilimentum that helps biologists distinguish between species by only looking at the webs.

There are five species of Argiope in North America, with a sixth (Bruennich's Argiope, Argiope bruennichi) potentially present in Alaska.  Of the five species in the continental United States, three have fairly restricted ranges.  The Silver Argiope (Argiope argentata) is primarily known from the southern parts of California, Texas, and Florida, as well as from Arizona.  A similar species, Argiope blanda, is known in the United States only from the southern tip of Texas.  Florida Argiope (Argiope florida) can be found in the southeastern United States, from North Carolina to Florida and west to Louisiana; it may also be found in Arizona.  The other two species are widespread.  The one I see most frequently is the Black-and-yellow Argiope (Argiope aurantia).

Female Black-and-yellow Argiope, dorsal side.

 Black-and-yellow Argiopes have a characteristic black and yellow pattern on the back of their abdomen, whereas the carapace is covered in silvery hairs.  The legs are mostly black but often have reddish or orangish coloration at the proximal end.  Black-and-yellow Argiopes also have distinctive yellow and black coloration on their undersides.  You can find this species of spider in old fields, wet meadows, riparian areas, and gardens.


Female Black-and-yellow Argiope, ventral side.

 The other widespread species is the Banded Argiope (Argiope trifasciata).


Female Banded Argiope, dorsal side.

 Banded Argiopes are identified by the yellow, black, and silvery-white stripes on the back of their abdomens.  Like the previous species, the carapace of this species is covered with silvery hairs.  The legs of the Banded Argiope are striped black and orangish-brown.  The underside of the abdomen of the Banded Argiope is also distinctively patterned with black and yellow.  You can find the Banded Argiope in grassy and shrubby areas that are usually a bit drier than where you find the Black-and-yellow Argiope, but the two can be found in the same area.


Female Banded Argiope, ventral side.

 One of my observational differences in the females of these two species is that the Black-and-yellow Argiope seems to drop from her web fairly quickly when I bump into it, whereas the Banded Argiope seems to hold her ground.

If you are one of those people who is deathly afraid of spiders, I hope that this at least gives you a better respect for the argiopes.  If you are one who likes spiders, be sure to get out in the next couple of weeks before it gets too cold to admire these large black and yellow arachnids.

Mid-winter Waterfowl Survey

On 9 January 2010, Brian Miller, Jason Hughey, Lindsay, and I participated in the Mid-winter Waterfowl Survey. Armed with binoculars, a spotting scope, and a clipboard with data sheets, we covered three sites along the St. Joseph River that had been surveyed in the past (Bercado Shores, Merrifield Park, and Veteran's Park); we also added two new sites (Mishawaka Riverwalk and St. Joseph's Lake at Notre Dame). As expected, the most abundant and frequent species that we encountered during our surveys was Mallard (Anas platyrhynchos, below).


We also saw Canada Goose (Branta canadensis) at four of the five sites, including nearly 600 at Merrifield Park. Our next most common observations were American Coot (Fulica americana), at two of the sites, and Hooded Merganser (Lophodytes cucullatus), at three of the sites. A handsome male "hoodie" in breeding plumage on St. Joseph's Lake is shown below.


Species that we saw less frequently included Lesser Scaup (Aythya affinis, at Veteran's Park), Bufflehead (Bucephala albeola, at Merrifield Park), Common Goldeneye (Bucephala clangula, at Merrifield Park), and Common Merganser (Mergus merganser, at St. Joseph's Lake). Pied-billed Grebe (Podilymbus podiceps) and Domestic Duck were also observed at several locations but were not on our data sheets. We also encountered at least two mature Bald Eagles (Haliaeetus leucocephalus), one at Merrifield Park (we also saw one at Mishawaka Riverwalk that we think was the same bird), and one at St. Joseph's Lake. While at St. Joseph's Lake, I had stopped to scope ducks and noticed that all of the Ring-billed and Herring Gulls (Larus delawarensis and Larus argentatus) that had previously been on the lake were instead in the air and appeared agitated. I mentioned this to Lindsay and asked rhetorically if there was an eagle nearby. Without missing a beat, she replied, "Yep, right there!" I looked in the direction of "there" to see a mature Bald Eagle, which proceeded to circle low over the lake and make several fruitless diving attempts at fish before flying out of view.

An added incentive to being outside and doing surveys such as this is the "bonus" species that you encounter that are not targets for your survey. While at St. Joseph's Lake, we heard a very distant rattle that we thought sounded like a Belted Kingfisher (Megaceryle alcyon). After several minutes, the rattle got closer and sounded more distinctly like a kingfisher. Shortly after, I found the male Belted Kingfisher shown below. In most bird species that exhibit sexual dimorphism, the male is the more colorful of the two sexes; this is not the case in Belted Kingfishers. The male is almost entirely blue and white, whereas the female has a rufous band across the chest (below the blue band) that extends down the flanks.


Although waterfowl were our target for the day, the most bizarre thing that we saw was a spider hanging out in the snow. We were amazed that this 3/4 inch long arachnid, shown in the photograph below, was out in 20 degree Farenheit weather, and without a hat and gloves nonetheless! According to Tom Murray on http://www.bugguide.net/, spiders tolerate the cold and can even be found on the snow. I think this is one of the longjawed orbweavers in the genus Tetragnatha, but if anyone can positively identify it, please do so.


Many people think that with the snow and cold weather comes an absence of wildlife, but this is not at all the case. Don't be scared off by sub-freezing temperatures; get out there and see what you can find!