Poisonous Spiders in Colorado?

For a lot of travelers, the mere mention of spiders is a bit concerning. The whole idea of a creature with two eerie body parts, an cephalothorax and abdomen, made up of an exoskeleton and jointed appendages creates trepidation.

In some cases of envenomation, a component in the venom (an enzyme) called sphingomyelinase D breaks down the sphingomyelin found in our tissue cell walls. Photo: Eran Finkle The yellow sac spider is a nocturnal creature, preferring to stalk its prey under the cover of darkness.

These are quite harmless, however, they spin a heavy silk web which could incite a pretty active reaction if you walked into one. Photo: patrickkavanagh The wolf spider is one that refuses to spin a web, preferring to stalk its prey. Photo: Allan Hopkins The banded garden spider is pretty true to its name, preferring to occupy space between plants in garden-style settings.

Another unusual aspect of this little critter, is that it keeps its dark underside pointed south, believed to allow it to absorb extra solar energy. If you are bitten, it will likely be painful because of these fangs, but it shouldnt require more medical attention than keeping the site clean to avoid infection. Photo: Judy Gallagher The running crab spider prefers to chase its prey down rather than spin a web and wait.

These spiders will run away when you approach and unless you intentionally grab one or pose a threat to a mother protecting her young, the likelihood of being bitten is slim. Photo: Elizabeth Nicodemus The eastern parsons spider is another nocturnal hunter preferring to hide in small cracks or under rocks during the day. As you explore the great outdoors of Colorado or settle into a new home, be confident that most spiders you might see are fairly friendly guests to have around, just like most snakes are harmless.

Does Colorado have any poisonous spiders?

There are really only two species of dangerous Colorado spiders that can do damage to a person with a bite. And of those two species, only one that truly calls Colorado home – the Black Widow.

Can brown recluse be found in Colorado?

The brown recluse, and all other recluse spiders, are extremely rare in Colorado. Confirmed specimens at the Denver Museum of Nature and Science collection include only one specimen of Loxoceles reclusa collected from the state (Boulder County, 1996).

What do spider bites look like in Colorado?

A red (or orange) hourglass-shaped marking on its under-side. Causes immediate local pain and swelling. Sometimes, you can see 2 fang marks at the bite site. Severe muscle cramps (especially stomach cramps) occur within 1 to 6 hours.

Are Colorado jumping spiders poisonous?

All jumping spiders have noticeably large front eyes, incredibly good eyesight, hunt during the day (unlike the majority of spiders, which are nocturnal). These guys would rather jump away from things as large as a human and are not known to be harmful. They can bite, but their venom is not dangerous to humans.

There are really only two species of dangerous Colorado spiders that can do damage to a person with a bite. And of those two species, only one that truly calls Colorado home the Black Widow.

It can also be beneficial to control other insects on your property, such as cockroaches, in order to remove a food source for the widows and prevent them from becoming abundant around your home. Unlike the neurotoxin effects seen in widow spider bites, the venom of a brown recluse causes tissue death.

However, in a small percentage of cases, a few hours after the bite, a bluish patch may begin to form and develop into a blister. However, the best known of the recluse spiders found in the U.S. Loxosceles reclusa occurs in many of the midwestern and south central states, and can be very common in and around homes in eastern Kansas, Missouri, Arkansas, Louisiana, Oklahoma, and parts of Texas.

Brown recluse and related recluse spiders (Loxosceles spp., Family Sicariidae) are, by far, the most commonly misidentified spiders in Colorado. Unfortunately, also greatly overdiagnosed are purported spider bites caused by brown recluse spiders a situation perpetuated by many in the Colorado medical establishment as well as through self-diagnosis.

The arrangement of the eyes on the recluse spiders is one pair in the front, the other two along the sides, forming a semicircle. On the cephalothorax (the body region including the head and legs) a brown marking is usually present.

The legs have a silky appearance, covered with fine hairs and large spines are not present. Eyes3 pairs, of approximate equal size, arranged in semicircular pattern.CephalothoraxOverall color uniformly brown; Darker brown pattern in center, somewhat resembling a violin, usually present.AbdomenOverall color uniformly brown, without any patterning.LegsUniformly colored, without any banding or patterning; Silky appearance due to fine hairs; no spines present.ActivityActive at night; restricted to web-lined refugia during day.WebsWebs are not produced in open areas where they are readily seen. In addition, the Mediterranean recluse, Loxosceles rufescens, is occasionally introduced and likely now established in many parts of the country, although nowhere is it considered to be common.

Specimens of Loxosceles that are collected from Colorado currently can be identified by personnel at the Denver Museum of Nature and Science. Nine protein fractions have been identified in the venom with most attention given to the enzyme sphingomyelinase D, considered the main contributor to cell injuries resulting from bites by these spiders. However, it has been suggested that bites of the common South American species, L. laeta , are potentially even more dangerous.

Conversely, only very few cases of complications are reported from the ubiquitous Mediterranean recluse ( L. rufuscens ) and the native southern California species, L. deserta, suggesting that these are less important medically. Brown recluse bites initially may be felt as a slight pinprick or not noticed at all. This may progress into an irregular lesion, an inch or two in diameter, with surrounding redness and sensitivity to touch.

This ulcerated area is dry, since capillaries are sealed by the effects of the venom, but it may take a couple of months to heal with permanent scarring sometimes produced. Clearly incidence of these spiders in Colorado is incidental, resulting from occasional transfers coming from chronically infested areas of the country. (There are two fairly credible reports of some species of Loxosceles established in a basement area; one each in Pueblo and Prowers counties.

CA-MRSA outbreaks are occurring with ever increasing frequency throughout the country in hospitals, prisons, and among members of athletic teams. This bacterial strain can result in lesions similar to those caused by bites of Loxosceles reclusa . Medical conditions with symptoms sometimes confused with brown recluse spider bites (adapted from Vetter 2000).Bacterial Methicillin-resistant Staphylococcus
aureus (MRSA or false spider bite diagnosis)
Other Staphylococcus infections
Streptococcus infection
Gonococcal arthritis dermatitis
Cutaneous anthrax Reaction to drugs
Warfarin poisoning Viral Infected herpes simplex
Chronic herpes simplex
Varicella zoster (shingles) Arthropod-induced Lyme disease
Rocky Mountain spotted fever
Ornithodoros coriaceus bite (soft tick)
Insect bites (flea, mite, biting fly) Fungal Sporotrichosis
Keratin cell mediated response to fungus Topical Poison ivy/poison oak
Chemical burn Lymphoproliferative disorders Lymphoma
Lymphomatoid papulosis Underlying disease states Diabetic ulcer Vascular disorders Focal vasculitis
Purpura fulminans
Thromboembolic phenomena
Polyarteritis nodosa Miscellaneous/Multiple causative agents Pyoderma gangrenosum
Pressure ulcers
Stevens-Johnson syndrome
Erythema multiforme
Erythema nodosum
Toxic epidermal necrolysis
Lyell syndrome

Several spiders found in Colorado and some other arachnids are commonly mistaken for brown recluse. Indoor migrations are greatest in late summer and early fall as the mature spiders wander in search of mates and cooler outdoor temperatures. The majority of these migrants are males, which possess conspicuous, paired bulbous structures from the head region that superficially may appear as fangs.

However, they can readily be distinguished based on several features: body is hairy; four pairs of eyes; and legs that are often are banded or patterned. Funnel weaver spiders common in the state usually are in one of three genera: Tegenaria spp., Agelenopsis spp., Hololena spp. Particularly common around homes in Colorado are the species Tegenaria domestica, Agelenopsis pennsylvanica , and Hololena hola .

The two types of cellar spiders found in Colorado that are sometimes mistaken for brown recluse are Pholcus phalangioides and Psilochorus spp. Along with funnel weavers, the wood louse hunter, Dysdera crocata , is also commonly mistaken for a brown recluse. These are densely clustered in a small area in the center of the head, not spread out on the cephalothorax in three pairs as with the recluse spiders.

However, the following features are useful to distinguish these from recluse spiders: very large jaws tipped with long fangs; cephalothorax and legs uniformly colored reddish brown; and the abdomen is uniformly of lighter brown or tan color. The running crab spiders are active hunters normally found searching for insect prey among plants, but they occasionally wander into homes. Their body form is somewhat similar to the more common crab spiders (Thomisidae family) with a generally rounded abdomen and the front two pairs of legs being longer than the others.

They are variable in color but some have dark markings that may cause confusion with the violin pattern of the recluse spider. The running crab spiders can be distinguished from recluse spiders by: second pair of legs is longer than the other legs; four pairs of eyes, in two rows; somewhat flattened body form; and dorsal marking, if present, is often located on the abdomen and is not distinctly a violin pattern. Sunspiders are readily distinguishable from spiders by the presence of long leg-like pedipalps arising from near the front of the body.

Medical myth: idiopathic wounds are often due to brown recluse or other spider bites throughout the United States.

The Hobo Spider isn’t considered a particularly venomous species, but there are some scientists that say it can become very aggressive if someone was to get near it’s eggs. The CDC may not consider it a dangerous spider, but I’d still want to stay away. It can be found throughout the entire state.

Benefits and Dangers of Spiders

Spiders are predators that either trap their prey in webs or actively hunt their insect prey. Spiders are very beneficial though, especially when they hunt and entangle other pests. So, if you’re one who becomes horrified at the thought of spiders, let’s see if we can give you a new perspective of how these eight-legged critters help us.For most, the least desirable way to be introduced to these hunters is to wander through one of their webs. However, spiders are not seeking human contact and would rather avoid it if possible. Encounters with these wildlife creatures in Colorado don’t occur every day and they can definitely be avoided.If you keep a watchful eye out for their webs and avoid areas where spiders like spinning them, your exploration of this beautiful state can be enjoyed without any unwelcome introductions to the many species of spiders considered native to Colorado. Learning about them should help you feel a little less anxious if you spot one.

Spiders Found in Colorado

The lists below contain some of the spiders found in Colorado, starting with some of the more dangerous ones. It’s worth mentioning that some spiders end up in the area by accident, after climbing into things like suitcases and cars. So, it’s possible, but incredibly unlikely, you could find a completely new spider species along your journeys.The following spiders can be encountered in Colorado. They may startle you on occasion or deliver a minor bite that requires cleaning, but other than that they are mostly harmless to humans.

Black Window Spider

*The brown recluse is neither native nor common in Colorado but has been found here. We list it because other species of spiders are often misidentified as brown recluse since they share a similar color and pattering. The brown recluse has a unique violin-shaped marking on its back. Very unique to this spider is that they have three sets of eyes, with one in the front and two on the sides. Most local Colorado spiders have four sets.Their venom is quite potent, but generally not fatal. If you’re bitten, Dr. Paula E. Cushing, Senior Curator of Invertebrate Zoology, Denver Museum of Nature & Science, past president American Arachnological Society and International Society of Arachnology, shares this:

Yellow Sac Spider

The yellow sac spider is a nocturnal creature, preferring to stalk its prey under the cover of darkness. The only web this spider spins is a small sac-like web to sleep in snug as a bug. Not really preferring to hang around humans, this spider will bite if it feels threatened. The bite can become red, irritated, and be painful for a short time (one or two hours). The bite will heal on its own, so keeping the bite clean should suffice.

Tarantula Spider

The tarantula is a large, hairy spider which some people keep as a pet. The bite from these critters can cause some discomfort and the hair-like setae can be irritating if it gets on your skin. These guys are not known to cause any real harm to humans even though they are a bit scary looking.

Funnel Web Spider

The funnel weaver or funnel web spiders are pretty common in and around the home. These are quite harmless, however, they spin a heavy silk web which could incite a pretty active reaction if you walked into one. These guys are often confused with their lighter brown cousins, the Brown Recluse (mentioned above).

Wolf Spider

The wolf spider is one that refuses to spin a web, preferring to stalk its prey. It is quite aggressive towards those insects it views as food, however, this guy really doesn’t want to be around you…at all. This spider can bite and cause some localized numbness, however, the venom does not pose a danger to humans. Keeping the bite area clean to avoid infection should be all you need. Colorado is home to multiple variants of the Wolf Spider, so keep an eye out for them. They’re so big sometimes they are mistaken for tarantulas.

Banded Garden Spider

The banded garden spider is pretty true to its name, preferring to occupy space between plants in garden-style settings. It spins its web low to the ground and in the shape of an orb which makes it fairly unique as well. Another unusual aspect of this little critter, is that it keeps its dark underside pointed south, believed to allow it to absorb extra solar energy. Often, this spider sits with its legs in pairs, making it appear as if it has four thick legs, rather than eight skinny ones. This spider is not dangerous to humans and is a gardener’s favorite as it helps control bugs within garden plants and shrubs.

Apache Jumping Spider

The apache jumping spider does not await their prey, choosing to pounce on their intended victims. All jumping spiders have noticeably large front eyes, incredibly good eyesight, hunt during the day (unlike the majority of spiders, which are nocturnal). These guys would rather jump away from things as large as a human and are not known to be harmful. They can bite, but their venom is not dangerous to humans.

Woodlouse Spider

The woodlouse spider or “roly-poly hunter”, feeds primarily upon woodlice. As the secondary common name implies, this spider can pick up nicknames based upon the things they might be feeding on when they are seen. If you are not actively picking up logs, rocks and bricks, the likelihood of finding one of these arachnids is pretty remote. These spiders have fairly large fangs considering their size. If you are bitten, it will likely be painful because of these fangs, but it shouldn’t require more medical attention than keeping the site clean to avoid infection.

Running Crab Spider

The running crab spider prefers to chase its prey down rather than spin a web and wait. So as you can imagine, they are quite fast, easily out-maneuvering your hand should you feel the urge to catch one. A well-camouflaged mottled brown coloring on this critter makes it hard to see, but that’s okay, this species is not harmful to humans.

Striped Fishing Spider

The striped fishing spider lives around lakes and docks giving it the nickname of “dock spider”. This critter skims along the water’s surface hunting insects, tadpoles and very small fish. These spiders will run away when you approach and unless you intentionally grab one or pose a threat to a mother protecting her young, the likelihood of being bitten is slim. Although it is a rather large spider, it is not considered harmful to humans.

Eastern Parsons Spider

The eastern parsons spider is another nocturnal hunter preferring to hide in small cracks or under rocks during the day. It’s generally found in woodpiles and around rocky terrain, though it will be enticed into the home if there are plenty of insects to hunt. This spider’s bite can break the skin but it is no threat to humans.

Bridge Orb Weaver

The bridge orb weaver is a spider that prefers to reside on steel objects. Bridges and other steel structures, particularly near lights, are its most favored locations. Its bite can break the skin, however, the toxicity of their venom won’t cause any damage to humans.

Cellar Spider

The cellar spider, or more often called daddy long-legs spider, is really common. Preferring to eat ants, these creatures will also hunt other insects including other spiders. These house-dwellers appreciate a warm and “inviting” home that protects them from the weather. They can be found most anywhere though, such as rock piles and loose mounds of leaves. One big misconception is these guys are harmful to humans. They do have venom, though it is not considered harmful to humans.

Identification

Brown recluse and related recluse spiders (Colorado hosts a great many kinds of spiders that are brown or have some patterning that may superficially resemble brown recluse spiders. However, close examination can readily distinguish them (see Table 1).

Recluse Spiders in the United States

There are 10 native recluse spiders (Identification of the various Loxosceles to the species level can only be done by an expert. Specimens of Loxosceles that are collected from Colorado currently can be identified by personnel at the Denver Museum of Nature and Science. The best known of the recluse spiders found in the U.S. is the brown recluse, Loxosceles reclusa. It occurs in many of the midwestern and south central states, and can be very common in and around homes in eastern Kansas, Missouri, Arkansas, Louisiana, Oklahoma, parts of Texas, and some other states. Occasionally it is transported out of its normal range, but it rarely survives and establishes outside the area.Most, if not all, of the recluse spiders have venom that can cause tissue death (cytotoxins). Nine protein fractions have been identified in the venom with most attention given to the enzyme sphingomyelinase D, considered the main contributor to cell injuries resulting from bites by these spiders.The amount of venom introduced during a bite, and possibly the toxicity of the venom, varies among the recluse spiders. For example, the medical importance of the brown recluse is well documented in the literature. However, it has been suggested that bites of the common South American species,

Symptoms of Brown Recluse Bite

Brown recluse bites initially may be felt as a slight pinprick – or not noticed at all. The majority of bites result in no further effects. Even if bitten, spiders may not introduce any venom which results in a dry bite.In a small percentage of cases, an irregular red area develops around the bite area within 2 to 8 hours and the site becomes painful and itchy. A small blister may develop at the bite site. Typically this heals normally with no further effects.In a small fraction of these cases, further complications can develop. A bluish sinking patch, with the central blister, may occur within 24 to 72 hours after a bite. This may progress into an irregular lesion, an inch or two in diameter, with surrounding redness and sensitivity to touch. This can further expand exposing underlying tissues as the dead cells slough away. This ulcerated area is dry, since capillaries are sealed by the effects of the venom, but it may take a couple of months to heal with permanent scarring sometimes produced.

Recluse Spiders in Colorado

The brown recluse, and all other recluse spiders, are extremely rare in Colorado. Confirmed specimens at the Denver Museum of Nature and Science collection include only one specimen ofClearly incidence of these spiders in Colorado is incidental, resulting from occasional transfers coming from chronically infested areas of the country. Establishment and sustained breeding of these spiders in Colorado is much rarer, if it occurs at all. (There are two fairly credible reports of some species ofDespite the near total lack of

Colorado Arachnids Mistaken for Brown Recluse Spiders

Several spiders found in Colorado – and some other arachnids – are commonly mistaken for brown recluse. These include the following:Funnel weavers also very commonly enter homes. Indoor migrations are greatest in late summer and early fall as the mature spiders wander in search of mates and cooler outdoor temperatures. The majority of these migrants are males, which possess conspicuous, paired bulbous structures from the head region that superficially may appear as fangs. However, these structures are pedipalps, used only to transfer sperm.Funnel weaver spiders are the group most commonly mistaken for recluse spiders in Colorado. However, they can readily be distinguished based on several features: body is hairy; four pairs of eyes; and legs that are often are banded or patterned.Funnel weaver spiders common in the state usually are in one of three genera: Tegenaria spp., Agelenopsis spp., Hololena spp. Particularly common around homes in Colorado are the speciesConfusion of these spiders with the brown recluse sometimes occurs because of patterning that may be found on the body, superficially resembling the violin pattern notable on the brown recluse. However, the cellar spiders commonly encountered can readily be distinguished based on several features: very long legs; body form that is longer than wide; eight eyes, often in two clusters of three eyes with a pair of eyes in between; and they are almost always associated with a web.The two types of cellar spiders found in Colorado that are sometimes mistaken for brown recluse areThis is one of the very few spiders, along with the recluse spiders, that also have three pairs of eyes. These are densely clustered in a small area in the center of the head, not spread out on the cephalothorax in three pairs as with the recluse spiders. However, the following features are useful to distinguish these from recluse spiders: very large jaws tipped with long fangs; cephalothorax and legs uniformly colored reddish brown; and the abdomen is uniformly of lighter brown or tan color.Two genera of running crab spiders most commonly cause confusion with recluse spiders,Most wolf spiders are drab colored, but some may have darker patches on the body. These typically are in the form of two longitudinal stripes, but they are sometimes confused with the violin pattern of the recluse. Wolf spiders can be separated from recluse spiders by several features: four pairs of eyes with the two upper pair much larger than the lower pair ; hairy body form; and an abdomen that is longer than it is wide.The most commonly encountered species around homes are those in the generaSunspiders are readily distinguishable from spiders by the presence of long leg-like pedipalps arising from near the front of the body. This gives them the appearance of having five pairs of legs. Sunspiders also have a very large cephalothorax with prominent forward-projecting jaws. These are used to capture and crush insect prey. Sunspiders do not possess venom glands.