How to Identify Spiders in Oregon

How to Identify Spiders in Oregon
In Oregon, observant naturalists can find four main types of spiders: jumping spiders and crab spiders (which are non-web building spiders, also called "wandering" spiders) and cobweb-weavers and funnel-web spiders (the web-building spiders). Identifying individual species is difficult without a complex identification key---over 300 species of jumping spider alone are found in North America. If you'd like more than a general classification, take notes in the field about size, coloration, location and behavior and consult an identification key when you get home. But distinguishing between the four general types of spider in Oregon is relatively easy.

Instructions

Difficulty: Moderate

Jumping Spiders

Things You’ll Need:
  • Plastic sandwich baggie Ruler Magnifying glass Notebook Pencil or pen
  • Plastic sandwich baggie
  • Ruler
  • Magnifying glass
  • Notebook
  • Pencil or pen
Step 1
Watch the spider move. Jumping spiders walk quickly in a halting motion on short legs---move several lengths, stop a bit, repeat. These spiders hunt their prey by sneaking up on it and then pouncing. If they come to a gap, they will jump across it, towing a safety cable of silk long enough to reach their landing. If threatened, they may also leap away. They can jump up to 25 times the length of their own bodies.
Step 2
Look at the spider's eyes. Jumping spiders have two eyes that are prominent in the front of their large, squarish cephalothorax (head), two smaller eyes to the sides, and a row of four tiny eyes on top of the carapace. This arrangement gives the jumping spiders the appearance of having a recognizable face with a few extra eyes. These spiders are known for their excellent eyesight.
Step 3
Approach the spider with your finger or a pencil. Jumping spiders will sometimes hold their ground, raising their forelegs in a threatening posture. The other response is backing away from the perceived threat in short bursts or leaping to safety.
Step 4
Observe the coloration. Small black and white striped jumping spiders commonly found on house siding are called zebra spiders, species Salticus scenicus. Other species found in Oregon can be green, earth-toned, shiny metallic or red and black.

Cobweb Builders

Step 1
Observe the type of web. Orb weaving spiders make the classically shaped round spider's web with spokes and rows of sticky silk to trap flying prey. Common orb weavers in Oregon include the orange-brown colored garden spider (Araneus diadematus), similar in appearance to the European garden spider. Fully grown, this intimidating-looking spider has an abdomen the size of a dime, with long spiky legs. Typically they sit in the center of their web, but when disturbed will either vibrate the web by bouncing or run up one of the guywires and hide. Orb weavers hunt at night, reducing the mosquito population and eating many other insects.
Step 2
Test the strength of the silk in the web. If you find a messy-looking collection of silk threads in a dark corner or underneath a rock pile, but see no spider, tug gently on one line. Strong, rope-like, tough, unbreakable silk could indicate you've found a black widow's nest. The western black widow (Latrodectus hesperus) is found throughout Oregon but is more common outside the Willamette Valley, in drier regions. With her swollen black abdomen and long slender black legs, she is easily distinguishable from all other spiders. Generally they hang upside-down, exposing the bottom of the abdomen. The absence of a red hourglass is not an indication she is not dangerous---some adults do not develop the hourglass.
Step 3
Note the shape and size of the abdomen. Cobweb spiders generally have rounded abdomens, housing the silk glands needed to build cobwebs. Orb weavers, black widows and common house spiders (Steatoda species) all follow this pattern. Cellar spiders (Pholcus phalangioides), however, are skinny-looking and are often called "daddy long legs," a common name also awarded to harvestmen (not actually spiders), of the order Opiliones. Cellar spiders are most often found in human habitations and are difficult to find on the trail.

Crab Spiders

Step 1
Look at the legs. Crab spiders hold their first two pairs of legs out to the side, giving the appearance of a crab. These first four legs are longer than the hindmost four legs.
Step 2
Observe the behavior. Unlike jumping spiders, crab spiders hold very still and wait for their prey to come to them, often hiding inside flowers or on leaves and stems. If startled into walking, this spider can move forward, backward or sideways, much like a crab.
Step 3
Note the color of this spider. Crab spiders come in many shades, often matching their preferred habitat for camouflage.

Funnel-web Dwellers

Step 1
Measure the spider. Three species of large funnel-web spiders are common in Oregon: the giant house spider (Tegenaria duellica), the barn funnel weaver (Tegenaria domestica), and the hobo spider (Tegenaria agrestis). Size alone will not distinguish the three species from each other, but they are all an inch or more in diameter, legs included. Funnel-web dwellers prefer being on the ground, trapping prey on a sheet-like web spread out from their funnel-home.
Step 2
Look for stripes on the cephalothorax (head). If the spider has stripes, it is either an Agelenopsis or Hololena spider or maybe a wolf spider.
Step 3
Look for dark rings around the legs. If there are dark rings around the legs and no stripes on the cephalothorax, this could be a barn funnel weaver or a Hololena. If the legs do not have dark rings, this could be a hobo spider.
Step 4
Peer closely at the abdomen (the hind end, not the underside) with your magnifying glass. Is there a repeated chevron pattern, a herringbone pattern, or is the coloration solid and plain? Hobo spiders have a herringbone pattern of repeated chevrons on their abdomen. Plain or patternless abdomen means the spider is not a hobo. Orange to mohagany in color with smooth legs could be one of many species of Callobius spider.

Tips & Warnings

 
When out on the trail, catch a live spider in a plastic baggie for observation. Try not to disturb the web. For some species, you'll need to be quick. Let your beneficial bug-eater go when you are done observing. Look at the tips of the pedipalps, the antennae-like limbs near the mouthparts. Male spiders will have bulbous ones. They use their enlarged pedipalps to transfer their sperm packets to the female.
 
When out on the trail, catch a live spider in a plastic baggie for observation. Try not to disturb the web. For some species, you'll need to be quick. Let your beneficial bug-eater go when you are done observing.
 
Look at the tips of the pedipalps, the antennae-like limbs near the mouthparts. Male spiders will have bulbous ones. They use their enlarged pedipalps to transfer their sperm packets to the female.
 
Darwin K. Vest of Eagle Rock Research advises that in the event of a spider biting a person only an arachnologist (spider scientist) or other qualified person should attempt positive identification of a spider as a hobo spider.

Article Written By Kelly Schaub

A former zookeeper turned writer and copyeditor in 2006, Kelly Schaub has published dozens of non-fiction articles on pet care and other topics. Schaub is a member of Willamette Writers, the Editorial Freelancers Association, and Romance Writers of America. Schaub earned a Bachelor of Science degree in Zoology from Oregon State University and edits fiction professionally.

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