Following are some of the most common types of spiders found in Montana.
Kingdom Animalia, Phylum Arthropoda, Class Arachnida, Order Araneae (Spiders)
Class Arachnida – 8 legs not 6. Two body parts, cephalothorax and abdomen, not three (insects have head, thorax, abdomen). Includes spiders, mites and ticks, scorpions, daddy-long-legs (they are not spiders), windscorpions, whipscorpions.
Order Araneae – Spiders (over 3000 species in North America)
Although many spider bites can be painful or annoying, The only truly poisonous spiders in Montana are the two black widow species (both very docile and non–aggressive unless the female is protecting the egg sac), and the aggressive house spider, also known as the Hobo Spider, a nonnative. The brown recluse and yellow-sac spider have not been found in Montana contrary to popular belief, according to the most reliable sources.
Following are the families of spiders that are represented in Montana, in alphabetical order by family.
Family Araneidae - Orb-weavers / Garden Spiders
Probably the most impressive spider we saw as kids were the giant corpulent spiders hanging in their webs stretched between branches or fences: the spiders we called “Cookie Spiders.” We called these “Cookie Spiders” growing up…because some seemed as big and decorated as a cookie. As kids often do, we’d squash them and an incredible amount of juice splurted out. Now I know better, that the orb-weavers or common garden spiders are our allies and friends in our struggle with the garden pests, and I feel bad about it. “Legs rather stout and spiny. All eight eyes small, sub-equal, and seemingly grouped into pairs. Web is an orb with a closed hub. Their retreat is often away from the web....Orb weavers (Araneidae) are often brightly coloured with rounded abdomens, some with peculiarly angled humps or spines. However, there is considerable variation in size, colour and shape in this group. They are easily recognized because of their beautiful, large, round webs, on which they rest, head downward, waiting for prey. The webs consist of a number of radiating threads crossed by two spirals. The inner spiral begins in the centre, winds outward, and is made of smooth threads like the radiating threads. It covers only the central 1/3 of the web. The outer spiral begins at the edges and winds inward. It is made of more elastic, sticky threads, coated with a liquid substance. …” ...“Garden Orb Weavers are NOT dangerous (but can bite as can most spiders) and rid your garden of many unwanted insects. They only live for one season and die off as Winter approaches, leaving their egg sacs behind to hatch out next Spring.”
Examples: Araneus spp. - Garden or Cross Spider (Araneus diadematus), Marbled Orb Weaver (Araneus marmoreus), Shamrock Spider (Araneus trifolium) (lots of webs covered with dew at sunrise), Araneus spp. prefer to build their webs among tall grasses and shrubbery. Large bulbous abdomen and legs often ringed. Web a spiraling orb, spider usually hangs downward near center of web, or nearby resting site connected by signal line that lets it know when a struggling insect on web. Each night web taken down and replaced. If I recall correctly, Charlotte (of Charlotte's Web) was a Barn spider (Araneus cavaticus), which prefers shady locations. Shamrock orb-weaver. Mountains of sw Montana. “Shamrock or Pumpkin Spiders as they are called in different places scientific name is Araneus trifolium. A. trifolium is a spider which builds an orb-web and is classified in a group of spiders called orb-weaver spider. Colour is a characteristic that may help to identify a spider. A. trifolium is orange (though it may show up in a yellowish green or purplish form). Its large, bulbous abdomen is similar to a pumpkin. Measuring a spider's length also helps in its identification. A. trifolium is large, compared to other spiders. Size is an important way of distinguishing one spider from another. The abdomen also contains the stomach or crop. In the fall the abdomen and the entire spider grows quickly. The high vegetation the spider prefers produces an abundance of insect food; and in the fall there is a growth spurt when food is most plentiful. This sudden increase in size may be cause for the spider's "sudden" appearance. In fact, the spiders have been present all-year, but were much smaller and simply less noticeable. The spider tends to show up around Halloween - and that is how it got its common name "Pumpkin Spider."” (http://www.spiderzrule.com/shamrock.htm)
Other orb-weavers: Araniella spp., Argiope spp., etc. Examples: Laurel Montana. 2006. Orb web on backyard playhouse. “The largest and most striking of the orb weaving spiders is the banded Argiope spider (Argiope trifasciata). It is found in late summer and early fall among shrubbery and in gardens where they make a highly symmetrical orb web. Females are generally silvery, with dark and yellow striping. Males are rarely observed and are much smaller than the females. The banded garden spider is harmless.” (http://www.spiderzrule.com/banded06.htm). Another banded argiope from se Montana, dry, tall grasses, sagebrush, prickly pear. Legs striped brown and yellow, about size of nickel. (http://www.spiderzrule.com/banded.htm).
Family Agelenidae - Funnel web weaver spiders
“Spinnerets long, two segmented, and conspicuous. Eyes small, sub-equal, and arranged in two relatively short rows. Web is sheet or platform-like with a tubular retreat leading off from the center or one edge.” Spin sheets of nonadhesive silk. Funnel off to one side as hiding place. Above is 3-d barrier web- when flying insect hits web, it falls down on sheet, spider rushes out and drags it back to funnel where it eats. Grass spiders (Agelenopsis spp.) etc. (http://davesgarden.com/community/forums/fp.php?pid=8060106#b)
The most infamous member of this family in Montana is the Hobo Spider or Aggressive House Spider (Tegenaria agrestis) aka (Agelenidae tegenaria-agrestis) “Swift-running spider distinguished from non-poisonous funnel web spiders by chevron shape on its abdomen and legs which are not banded like other funnel web spiders.” Nonnative, the hobo spiders are from Europe, but were first seen in Seattle in the 1930s, and have slowly been spreading eastward. I never saw any growing up in the 1960s or 1970s, but they had spread into western Montana by the 1980s. Hobo spiders had not made it to eastern Montana as of 2008, but they are in Montana. (http://pep.wsu.edu/pdf/PLS116_1.pdf)
Family Dictynidae - Dictynid Spiders
Dictyna major and Dictyna coloradensis - light gray with a dark stripe down their backs. Webs often light upside down pyramid. Many invasive plants have provided more places for these native spiders to nest, ex. Sulfur cinquefoil, spotted knapweed, leafy spurge. (http://www.loe.org/shows/segments.html?programID=11-P13-00039&segmentID=6)
(NOT IN MONTANA) Family Loxoscelidae – Violin / Recluse Spiders
I am only listing this spider here because so many people falsely believe there are brown recluse spiders here in Montana. “Distinctive violin-shaped marking on the cephalothorax. The six eyes are arranged in three pairs forming a semicircle.” They do not spin webs. Violin Spider aka Brown Recluse Spider (Loxosceles reclusa) Not in Montana.
Family Lycosidae – Wolf Spiders
“Eyes arranged in three rows with four large eyes on top and front of head and anterior, slightly curved row of four small eyes. Females carry the globular egg sac attached by the spinnerets. The fourth pair of legs is the longest and frequently held stretched out behind the spider.” These spiders do not use webs. They are some of the largest spiders in Montana and run around after their prey, using their speed and visual acuity, moving into houses in the fall. Most live on ground and hunt at night. Only one group spins web (Pardosa spp.), others live under rocks or holes in ground. Burrowing Wolf Spiders (Geolycosa spp.) - The one that pretty much stays in its burrow and only runs out to kill; hides in burrow if senses vibrations like someone walking. There are many species of running wolf spiders (Lycosa spp.)
Family Oxyopidae – Lynx Spiders
Little spiders that hide and wait with front legs often raised and jump in fields with tall grass and herbaceous plants, but do not make webs or retreats. Mostly tropical but at least one common type in the Rockies, the Jumping Lynx Spider (Oxyopes spp.)
Family Pisauridae – Nursery Web Spiders
Include fishing spiders that run across water, swim, etc. In Montana there is the Six-spotted Fishin Spider (Dolomedes triton) in slow-flowing streams and ponds, where it will go after aquatic insects, or even small fish and tadpoles; found scampering over waterside plants.
Family Salticidae - Jumping Spiders
I have a fondness for these little guys. Square-fronted cephalothorax bearing four very large anterior eyes. Legs usually short and stout with the first pair sometimes enlarged. Diurnal. They do not use webs, but run around, and jump, using their speed and visual acuity to capture prey. They are small, but their little faces often look as though they see you or are looking back at you, before they spring quickly to their next location. “Jumping spiders and wolf spiders have two eyes much larger than the other six, probably an adaptation to help them better see their prey. Jumping spiders are small to medium sized spiders, usually stout bodied, short legged and hairy. They frequently have contrasting black, reddish, or yellowish markings. They are very agile, pouncing and feeding on small insects about the home. They are often seen on screens or near doors or windows.”
The most common jumping spiders in Montana are probably the Metaphid Jumping Spiders (Metaphidippus spp.) which are gray and brown, and are more common among plants, and the Daring Jumping Spiders (Phidippus audax) which are black with a gray/white crossband and are often seen hunting in the house, along the windowsills and sashes.
Family Sparassidae (formerly Heteropodidae) - Huntsman Spiders (nonnative)
Also called giant crab spiders, because of their size and appearance, they aren’t native to Montana, but they are sometimes found in houses as they can come in with bananas and other fruit. For example, one was found in a home in a western mountainous forested area.
Family Tetragnathidae – Large-jawed Orb Weavers
Extra large powerful jobs; one species is spread throughout U.S. and Canada and so is probably Montana, the long-jawed orb weaver (Tetragnatha laboriosa)
Family Theridiidae – Comb-Footed Spiders
“Medium to small sized, glossy spiders with globular abdomens, thin legs bearing few spines, and eight relatively large, protuberant eyes.” I have at times had to do a double-take in a basement or outhouse, because the American House Spider (Achaeranea tepidariorum) or House spider (Steatoda sp.) looks small, dark and jewel-like, similar at first glance to a black widow. The house spiders are dark brown, unlike the black widow, and they don't have the red/orange hourglass that female black widows have under their abdomens. There are two species of black widow in Montana: Western Black Widow Spider (Latrodectus hesperus) and Northern Black Widow (Latrodectus variolus ).
Family Thomisidae - Crab or Ambush Spiders
They hold their legs out to the sides like a crab. Wander over ground and plants in search of prey. “First and second pair of legs distinctly longer and stouter than the third and fourth. Abdomen usually broad at the posterior. Crab spiders are commonly seen on flowers, do not construct a web, and are typically brightly colored.” “Crab or ambush spiders are somewhat crab-like in shape and walk sideways or backward. They are medium sized and often brightly colored, with abdomens that are usually wide at the posterior end. The two front pair of legs are usually longer and stouter than the two hind pair and crab spiders often hold their legs poised to trap insect prey. They have eight relatively small, well spaced, light colored eyes. Crab spiders are usually found outside in gardens and landscaping where they spin no webs but forage for their prey or lie in ambush on blossoms or other parts of plants; some on wood fences. They are able to gradually change colors to match flowers for camouflage.” Crab spiders in Montana include the Goldenrod spider (Misumena vatia), the Flower Spider (Mimusa asperatus), the Elegant Crab Spider (Xysticus elegans), and the Thrice-banded Crab Spider (Xysticus triguttatus). There is another group called Inconspicuous Crab Spiders (Philodrumus spp.) that rest on tree bark, and are sometimes separated into their own Family Philodromidae.
By the way, if you sometimes see what looks like a spider that doesn't move for a long time, and you start thinking maybe it's dead, these “dead” spiders often really only the moulted skin off a spider that grew and needed a change.
MSU Extension Service MontGuide, Spider Identification and Management, by Gary L. Jensen, Will Lanier, and Catherine E. Seibert. MT 199210 AG Reviewed 3/05 (http://msuextension.org/publications/AgandNaturalResources/MT199210AG.pdf)
U.S. Spiders Identification Chart (not all in Montana). http://www.termite.com/spider-identification.html