Introduction
Note: This article deals only with the poisonous and venomous arthropods, not the ones that spread disease.
The purpose of this article is to assist you in determining whether the “bug” or spider you have found is potentially dangerous.
This article covers all of the potentially “dangerous” arachnids (spiders and their kin) and insects found in the United States.
Many people think that “bugs” are out to get them, which is completely untrue. Almost all “bugs” are harmless and are actually beneficial and only a few species are potentially harmful.
One thing to remember about “bugs” is you don’t bother them and they won’t bother you; however, if you need to remove an unwanted insect or spider, place a clear cup over it and slowly slide an index card underneath the cup.
Do not try to pick up the insect or spider, rather learn and observe without touching.
All of the arachnids and insects listed here are normally docile and are not aggressive. However, if you try to pick it up, or otherwise disturb it, some of the arachnids and insects will feel threatened and will defend themselves. Some of these defense mechanisms can be painful, or even harmful.
How to use
For a larger picture, click on the thumbnail. For more pictures, click on the
More Pictures links. For more information about a particular topic, click on the underlined links listed in the reference section below each topic. Also please check the
Guide Page links, as they will have more information about the range, habitat, and typical size of the specific arachnid /insect.
If you do not find your specimen listed here, then it is probably not dangerous.
If you are still unsure and would like confirmation, please submit your images
to the
ID Request page.
If your specimen is listed below, and you have additional questions, check the
General Discussion forum and post your question there.
All of the arachnids and insects shown here bite and sting only in defense, they will not bite/sting unless provoked.
Table of Contents:
Arthropods
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Centipedes
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Millipedes
Arachnids
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Scorpions
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Spiders
Insects
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Ants, Bees, & Wasps
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Beetles
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Flies
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Moths & Butterflies
Arthropods
Millipedes
More Pictures Guide Page
Many millipedes with bright color patterns secrete a compound containing cyanide. Wash your hands after handling them and do not allow children to pick them up.
A fact sheet on millipedes
A fact sheet on centipedes and millipedes
Centipedes - Larger species can inflict a painful bite on humans, but only if handled.
More Pictures Guide Page
Compare to
this image of a millipede
Centipedes only have one pair of legs per segment and have large antennae compared to millipedes, which have many legs per segment and very small antennae.
A fact sheet on centipedes
Another fact sheet on centipedes
A fact sheet on centipedes and millipedes
Arachnids
Spiders
Spiders are important controllers of pests and
only a very small number of species can or will bite humans even if provoked.
You have a better chance of dying from a bee sting than from a spider bite.
The only spiders in this article that are truly “dangerous” are the Black Widow and the Brown Recluse. Other than those, the bite of most spiders are comparable to a bee sting.
If you are ever bitten by any spider, capture it for identification as it can be important in determining the course of treatment.
Orb Weavers - Very common –
Extremely important controllers of pests - The chances of getting bitten by any species of orb weaver are slim to none
More Pictures Guide Page
Most orb weavers can or will not bite humans. The few species that will bite will only do so if squeezed or otherwise provoked. Typical reactions include localized pain with slight redness, which quickly subsides.
Wolf spiders –
Very important controllers of pests - The chances of getting bitten by any species of wolf spider are slim to none –
Wolf spiders will only bite if provoked
More Pictures Guide Page
The venom of wolf spiders is not very harmful to humans.
Wolf spiders will bite only if handled or if trapped next to the skin. Typical reactions include initial pain and redness subsiding with time.
References
“Commonly Encountered Pennsylvania Spiders” Covers several spiders found throughout the U.S.
Jumping Spiders –
Very important controllers of pests - The chances of getting bitten by any species of jumping spider are slim to none –
Jumping spiders will only bite if provoked
More Pictures Guide Page
Most jumping spiders can or will not bite humans. However, several species in the genus Phidippus are capable of biting. The bite results in localized swelling and redness.
References
“Commonly Encountered Pennsylvania Spiders” Covers several spiders found throughout the U.S.
Sac spiders - Chiracanthium inclusum - Chiracanthium mildei - Trachelas tranquillus
Several species of sac spiders are suspected of being responsible for most indoor spider bites to humans.
Like most spiders, sac spiders typically do not bite unless they are trapped against the skin or provoked. Sac spiders are nocturnal, therefore bites are most likely to occur at night.
Chiracanthium inclusum - Chiracanthium mildei
Chiracanthium mildei
More Pictures Guide Page
Chiracanthium inclusum is native to much of the United States, except for the northernmost states.
C. mildei is an introduced species from Europe. As of 1978, it was found throughout much of the Northeast; however, it is likely that it has greatly increased its range since then.
The bite of a yellow sac spider usually results in instant, intense, stinging pain, similar to the sting of a bee or wasp; localized redness; and a burning sensation lasting for up to an hour, with rash and blistering occurring during the next 1-10 hours. There is slight swelling at the site of the bite for a day or two. Sometimes an ulcerated lesion develops at the site of the bite. This ulceration normally heals itself within several weeks.
Trachelas tranquillus
Trachelas sp.
Trachelas tranquillus
More Pictures Guide Page
This spider ranges from New England south to Georgia and Alabama and west to Kansas and Minnesota.
There are records of severe secondary infection associated with the bite, which may result from the spider's propensity for feeding on dead arthropods. Typically, the bite results in redness and some swelling, similar to a bee or wasp sting.
References
Information on sac spiders
Information about the yellow sac spiders
“Commonly Encountered Pennsylvania Spiders” Covers several spiders found throughout the U.S.
More information on yellow sac spiders
Tarantulas –
Will not bite unless provoked – Their venom is no worse than most bee stings; however, some tarantulas can release a cloud of hairs that irritate the mucous membranes of mammals
More Pictures Guide Page
Tarantulas are huge spiders, with a distinctive, menacing appearance, which has given them an undeservedly sinister reputation.
A fact sheet on tarantulas
Black Widow – The bite of the adult female can be fatal -
Will not bite unless provoked
Female - Bottom view
Female - Side view
Female (on the left) and male (on the right) - Top view
More Pictures Guide Page
Black widows are nocturnal. During the day the female will hide in a secluded corner of her web. At night she will hang upside-down in the web which is built close to the ground.
The male black widow is not dangerous. The adult female black widow has a red hourglass (or part of) on the underside of the abdomen. The female black widow may also have red or white marking on the top of the abdomen.
The shape of the female black widow is distinctive and the spider has a smooth, hairless appearance.
Female black widows are only aggressive when they are protecting an egg sac, otherwise they will try to flee.
The female black widow has a notorious habit of eating the male after mating, but there are exceptions if the female is already well fed.
This is the most venomous spider in North America, but almost all healthy people who are bitten will recover in a few days. Very few deaths from black widow spider bites are reported in the U.S., but the risk of death from a bite remains.
The bite of a black widow may feel like a pin prick or the victim may feel nothing at all. Two red marks may appear where bitten, along with minor swelling. Pain will become intense within 1 to 3 hours, continuing for up to 2 days, and can spread from a bitten limb into the abdomen or back. Severe cramping or rigidity may occur in the abdominal muscles. The victim may also exhibit other symptoms including nausea, vomiting, shaking, profuse perspiration, and labored speech and breathing, possibly progressing to a weak pulse, clammy skin, unconsciousness, and convulsions. Symptoms often diminish after about a day and are gone after several days. Serious long-term complications or death from a black widow bite are very rare.
References
A fact sheet about the Black Widow
Information about the widow spiders
A fact sheet on the Black Widow, its bite, habitat, and how to get rid of it
Information about the widow spiders, their bite, symptoms of the bite, web, and life cycle
“Commonly Encountered Pennsylvania Spiders” Covers several spiders found throughout the U.S.
Steatoda grossa –
Will not bite unless provoked
More Pictures Guide Page
The bite of this spider can produce symptoms that are similar, but much less severe than those of a black widow bite. In some cases blistering may form at the site of the bite along with physical discomfort that lasts for several days.
References
Information about Steatoda spiders
“Steatoda spiders as competitors/predators of the Hobo spider”
“Commonly Encountered Pennsylvania Spiders” Covers several spiders found throughout the U.S.
Recluse spiders – Genus Loxosceles –
Will not bite unless provoked
Loxosceles sp.
Guide Page
Several species of recluse spiders are found in the U.S.; best known
is the infamous
Brown Recluse
If you do not live in any of the colored areas on the maps below, then it is quite unlikely that you have a recluse spider. Recluse spiders are only rarely transported outside of their range on or in furniture, boxes, and plants.
See
this map for the distribution of recluse spiders in the U.S.
See
this map for the distribution of the Brown Recluse.
The Brown Recluse has uniformly colored legs covered with fine hairs. The legs have no stripes, banding, or spines on them. The abdomen is also uniformly colored.
The body of the Brown Recluse is under half an inch in length.
Some species of recluse spiders have a well-defined dark violin-shaped marking on the “head” region of the spider with the neck of the violin pointing toward the abdomen; however this is not a conclusive way to identify a recluse spider. All recluse spiders have
six eyes whereas most spiders have eight (this can only be determined with the use of a microscope.)
For more information on how to identify a Brown Recluse see this link.
Recluse spiders are nocturnal, therefore most likely encountered at night when they are foraging for food. During the day recluse spiders hide in secluded places.
Little is known about the venom and bite of the lesser-known species of recluse spiders.
“Although there are suspected variations in virulence among the species, all Loxosceles spiders should be considered potentially capable of producing dermonecrosis (skin necrosis) to some extent.”
(1)
Most Brown Recluse bites result in only a small red mark and heal without serious complications.
An interesting fact is the Brown Recluse cannot bite through clothing because of its small fangs.
The bite of the Brown Recluse is usually painless and many go unnoticed for as long as 2 to 8 hours or the victim may feel a stinging sensation later followed by intense pain. A small white blister develops at the site of the bite, followed by swelling of the area. This swollen area enlarges and becomes red. The site becomes painful and hard to the touch. A necrotic lesion develops and the affected tissue dies and slowly sloughs away exposing the underling tissue. This necrotic ulcer may persist for several months and heals slowly, leaving a sunken area of scar tissue.
It is exceedingly hard for a physician to correctly diagnose a "brown recluse bite" based simply on the wound characteristics.
In extremely rare cases, a systemic reaction may occur. Systemic symptoms resulting from a brown recluse bite are kidney failure, black urine (from high levels of hemoglobin in it), and disseminated intravascular coagulation (small blood clots throughout the body).
References Cited
1 Vetter, R. S.
Arachnids Submitted as Suspected Brown Recluse Spiders
(Araneae: Sicariidae): Loxosceles Spiders Are Virtually Restricted to
Their Known Distributions but Are Perceived to
Exist Throughout the United States J. Med. Entomol. 2005; 42(4): 512-521
References
“How to Identify and Misidentify a Brown Recluse Spider”
Information about the Brown Recluse
A fact sheet on the Brown Recluse
A fact sheet on the Brown Recluse with information on how to get rid of it and about the bite
Information about the Brown Recluse and the misidentification of it and its bite
Myths about the Brown Recluse
More about recluse spiders and their bite
This image shows the eye arrangement of recluse spiders
More information on recluse spiders
A picture of the Brown Recluse
“Commonly Encountered Pennsylvania Spiders” Covers several spiders found throughout the U.S.
“Causes of Necrotic Wounds other than Brown Recluse Spider Bites”
Hobo spider
More Pictures Guide Page
The Hobo spider is native to Europe. In the U.S., it is commonly found in the Pacific
Northwest (See
this map).
It is very hard to positively identify a Hobo spider. If you think you have found a Hobo spider take it to a specialist.
“…evidence for hobo spider envenomation causing necrotic ulcers consists of one verified bite in a patient with a pre-existing medical condition known to cause ulcer disease, rabbit model bioassays, and many purported envenomations that could easily be ascribed to other etiologies.”
(2)
References Cited
2 Vetter, R. S., and Isbister, G. K.
Do Hobo Spider Bites Cause Dermonecrotic Injuries?
Ann Emerg Med. 2004; 44:605-607.
References
The Hobo spider website (Contains some out of date information)
“Steatoda spiders as competitors/predators of the Hobo spider”
“How to Identify (and Misidentify) a Hobo Spider”
Scorpions –
Will not sting unless stepped on or otherwise provoked
More Pictures Guide Page
In the United States, scorpions are most abundant in the semiarid regions of the Southwest.
The sting of most scorpions is not serious and usually results in localized pain, swelling, tenderness and some discoloration.
However, the sting of one scorpion,
Centruroides exilicauda, can be fatal. Most healthy adults are not at significant risk; the ones most at risk of dying from a sting by
Centruroides exilicauda are children. The site of the sting does not become discolored.
Centruroides exilicauda is found in southeastern California, Arizona, Nevada, southern Utah, and southwestern New Mexico.
References
A fact sheet about scorpions and how to get rid of them
Information about scorpions and their sting
Information about scorpions, their biology and how to get rid of them
An image of Centruroides exilicauda
Information about scorpions, their life cycle, and how to get rid of them
Insects
True Bugs – The larger ones can inflict a painful bite - The chances of getting bitten by any species of true bug are slim, unless you handle one.
More Pictures Guide Page
A small number of true bugs feed on the blood of vertebrates; aside from these, only the larger ones can bite humans, but only if handled
Ants, Bees, & Wasps – Order Hymenoptera
In ants, bees, and wasps the stinger is a modified egg-laying apparatus, so only females can give a venomous sting.
Bee and wasp stings account for almost all of the deaths by insects and arachnid bites/stings in the U.S.
Ordinarily,
Hymenoptera venom will only cause local pain and swelling.
However, some individuals, like me, may be allergic to
Hymenoptera stings. An allergic reaction to
Hymenoptera stings occurs once the victim becomes sensitized to the venom from a previous sting. The allergic reaction is caused by the immune system, which has now been oversensitized to the venom and releases histamines into the bloodstream. Histamines dilate blood capillaries, causing the skin to appear red and feel warm, and also makes the capillaries more permeable, which allows fluid to escape into the tissues. This causes swelling, which is manifested as rapidly appearing hives, accompanied by severe itching. In a severe allergic reaction called anaphylactic shock, the tissues of the throat swell and the victim may have difficulty breathing and, unless promptly treated, death may result
Ants, bees, and wasps will only sting if stepped on, handled or otherwise provoked.
Ants
It is very hard to separate the stinging and biting ants from the many species of harmless ants.
Harvester Ants
Harvester Ants
If the nest is disturbed, these ants bite the intruder and hang on tenaciously while inflicting a very painful sting. The reaction to the sting spreads along the lymph channels with pain lasting for several hours. There are 22 species of harvester ant in the U.S., with only one species (
Pogonomyrmex badius – Florida harvester ant) found east of the Mississippi River.
Fire Ants - Can inflict a painful sting
Red Imported Fire Ants
The Red Imported Fire Ant is the most notorious fire ant in the U.S. It was introduced from South America into the United States between 1933 and 1945. Fire ants get their name from their painful stings.
If their nest is stepped on, the workers rush out and sting the feet and legs of the intruder. Each sting results in a small, acutely painful wound that develops into a pustule in 24 to 48 hours. As the pustules heal they become itchy and can become infected.
Field Ants
Field Ants
These are medium-sized ants that occur throughout the United States and are quite common. When they bite they inject a secretion into the wound; because of this their bites are very painful.
References
Information on the Florida harvester ant
Information on Red harvester ants
“The ABC’s of Fire Ants and Their Management”
Information about biting and stinging ants
Information on the Red Imported Fire Ant
More information on the Red Imported Fire Ant
Yet more information about the Red Imported Fire Ant
Information on the Red Imported Fire Ant and how to get rid of it
Bee and wasp stings account for almost all of the deaths by insects and arachnid bites/stings in the U.S.
Bees - Can be deadly if the person is allergic to the venom.
Honey bees
Bumble bees
More Pictures Guide Page
Africanized honeybees (Killer bees) are more aggressive than ordinary honeybees. They guard a larger area around their hives, become upset more easily by humans and machinery, and respond faster and in larger swarms. They will chase threatening humans and animals for as much as a quarter of a mile. Africanized honeybees are from the southern part of Africa. They were brought to southern Brazil, and have since spread as far north as the southwestern U.S.
References
“Africanized Honey Bee Information In Brief” Deals manly with Africanized honeybees in California
Information about bees
A fact sheet about bee and wasp stings
Information about bee stings
Information about bee and wasp stings, allergic reactions to bee and wasp stings, and multiple stings
Information about how to avoid getting stung by bees and wasps
Information about bee sting allergies
Wasps – Can be deadly if the person is allergic to the venom.
Wasps have a smooth, lance-like stinger, meaning that they can sting repeatedly.
Paper wasps
Hornets
Yellowjackets
More Pictures Guide Page
Velvet Ant – (A kind of wasp) - Can give an excruciating sting if handled
More Pictures Guide Page
Tarantula Hawks
Tarantula Hawks can give an excruciating sting that acts more as a deterrent; causes intense pain but almost no damage at all.
Cicada Killer - Can give a very painful sting if handled or otherwise provoked.
Female with prey
Male
Guide Page More Pictures
Male Cicada Killers are very territorial, and will patrol almost constantly in a small area near a nest, flying at anything passing by.
The female hunts for cicadas and when she finds one she will capture and then sting it. The sting only paralyzes the cicada and the female wasp lays an egg on the cicada and then buries it alive as food for the larva. Females may have multiple underground chambers in a single nest with one larva in each chamber. Female Cicada Killers are not aggressive and will not sting unless grabbed or otherwise provoked.
References
A fact sheet on Cicada Killers
Information about wasps
A fact sheet about bee and wasp stings
Information about bee and wasp stings, allergic reactions to bee and wasp stings, and multiple stings
Information about how to avoid getting stung by bees and wasps
Beetles
Blister beetles
More Pictures Guide Page
Pressing or rubbing adult blister beetles may cause them to exude some of their
hemolymph (“blood”), which contains Cantharidin. Cantharidin causes blistering of the skin, thus the name blister beetle.
References
“Blister beetles in alfalfa” Also has information about blister beetle toxicity
Information about blister beetles and their effects on livestock
Moths & Butterflies
Some caterpillars, mainly those of moths, have stinging “hairs” that can cause an irritating reaction when touched.
Saddleback caterpillar
Buck Moth
Io Moth
Puss Caterpillar
Spiny Oak Slug Moth
Hag Moth
Stinging Rose Caterpillar
Hickory Tussock Moth
Family Arctiidae - Tiger Moths
Browntail Moth
An invasive species which, if touched, can cause a rash similar to that of poison ivy. The rash is the result of a toxin in the hairs and the barbed hairs becoming embedded in the skin. In sensitive individuals, the rash may be severe and persist for several weeks. If the hairs are inhaled, respiratory distress may result. In the U.S., the Browntail moth is found in many of the New England states.
References
Information about stinging caterpillars
A fact sheet about stinging caterpillars
More information about stinging caterpillars
Flies
Horse fly larvae – If they are handled roughly or trodden upon with bare feet they can inflict a very painful bite, but their venom is not dangerous to humans
Most horse fly larvae are found in water or moist soil. They are fierce predators, capturing their prey with their sharp sickle-shaped mandibles and paralyzing it with an injection of venom.
Note: Female horse flies feed on the blood of livestock, humans, and other large mammals and in doing so give a painful bite. Male horse flies feed only on nectar.
References
Information on horse and deer flies
More information on horse and deer flies
