Crab Spider: All You Need to Know for Easy Identification and Fascinating Facts

Crab spiders are fascinating creatures known for their unique appearance and hunting techniques. These spiders may display a variety of colors, such as greenish-yellow or yellow-brown, and have the ability to change their color to blend in with their environment, like the goldenrod crab spider.

These spiders are called crab spiders because of their crab-like shape, and their legs bend and extend sideways, similar to how a crab would walk. They are small to medium-sized spiders and are known for their hunting prowess rather than building webs.

Features of crab spiders:

  • Crab-like shape and leg orientation
  • Can change color to blend with surroundings
  • Spiny hairs covering their body
  • Excellent hunters

Characteristics of crab spiders:

  • Small to medium-sized
  • Solitary hunters rather than web builders
  • Can be found in various habitats, including flowers and foliage

By learning more about these fascinating arachnids, we gain a deeper understanding of the diverse and intriguing world of spiders that exists all around us.

Crab Spider Basics

Crab Spiders Vs Crabs

Crab spiders and crabs are quite different despite their similar names. To clarify:

  • Crab spiders are arachnids.
  • Crabs are crustaceans.

Thomisidae Family

Crab spiders belong to the Thomisidae family. They are also called “thomisid” crab spiders, or simply “thomisids.”

Physical Description

Size

Crab spiders are generally small in size, making them hard to notice.

Eight Eyes

Like most spiders, crab spiders possess eight eyes that help them detect their prey.

Front Two Legs

Crab spiders have longer front two legs compared to their back two pairs, which they use for hunting their prey.

Abdomen

These spiders have a distinct abdomen with unique patterns that can vary among species.

Comparison Table

Feature Crab Spiders Crabs
Classification Arachnids Crustaceans
Number of Eyes Eight Eyes Two Compound Eyes
Number of Legs Eight Legs Ten Legs (5 pairs)
Family Thomisidae Various Families
Habitat Gardens, forest, fields Aquatic environments

By understanding these basic features, you can easily differentiate crab spiders from crabs and appreciate their fascinating characteristics.

Species and Genera

Widespread Species

  • Misumena vatia (Goldenrod Crab Spider): A North American and European species known for its ability to change color from white to yellow, often found on blossoms. Females have an orange or reddish stripe on each side of the abdomen1.
  • Xysticus: A genus of crab spiders with many species found in North America, Europe, and Asia. They typically have a flat shape, with front two pairs of legs much longer than the back two pairs2.

Lesser-Known Species

  • Northern Crab Spider: This species has many spiny hairs covering its body and a great variety of possible color combinations. They can be difficult for even specialists to identify3.

Comparison Table

Species Distribution Coloration Key Features
Goldenrod Crab Spider North America, Europe White to yellow; orange or reddish stripe Color-changing, found on blossoms
Xysticus (genus) North America, Europe, Asia Varies Flat shape, long front legs
Northern Crab Spider North America Varies with many combinations Spiny hairs, challenging identification3

Behavior and Biology

Hunting Strategies

Crab spiders are ambush predators that utilize their legs and camouflage abilities for effective hunting. They mostly prey on insects such as flies, butterflies, and bees. Some examples of their hunting strategies include:

  • Lying in wait on flowers to catch unsuspecting pollinators
  • Staying motionless on tree bark or leaves to ambush passing insects
  • Moving sideways (similar to crabs) for quick capture of prey

Camouflage

Crab spiders have excellent camouflage, with their colors and patterns resembling their surroundings. They can be found in various habitats like meadows, woodlands, tropical rainforests, grasslands, and scrublands.

A few crab spider camouflaging features:

  • Ability to change color from white to yellow, depending on the blossom they inhabit (e.g., Goldenrod crab spiders)
  • Greenish-yellow or yellow-brown markings to blend in with foliage (e.g., Northern crab spider)
  • Spiny hairs covering their body for a more textured appearance

Predators and Self-Defense

Crab spiders have various predators, including birds, lizards, and other spider species like the huntsman spider (family Sparassidae). To protect themselves, they utilize their camouflage abilities and adopt self-defense mechanisms such as:

  • Retreating quickly when threatened
  • Biting when cornered, although their venom is generally harmless to humans
  • Protecting their egg sacs by building webs around them

Comparison Table: Crab Spider vs Huntsman Spider

Aspect Crab Spider Huntsman Spider
Hunting Strategy Ambush predators, wait on flowers or leaves Active hunters, chase down prey
Leg Position Legs extended to the sides Legs sprawled out and held close to the body
Camouflage Excellent, blend in with surroundings Moderate, rely more on speed for hunting
Habitat Meadows, woodlands, tropical rainforests, grasslands Mostly in tropical regions, under bark, and leaves

In conclusion, crab spiders exhibit impressive hunting strategies, camouflage abilities, and self-defense mechanisms, making them efficient predators in various habitats. Their behavior and biology are adapted to their environment, ensuring their survival and success in catching prey.

Reproduction and Life Cycle

Mating Season and Courtship

Crab spiders have a fascinating reproductive process. Their mating season varies according to their habitat and species. These spiders are known to adapt to their environment, allowing them to thrive year-round.

Males often engage in an elaborate courtship ritual to attract females. They perform a series of intricate movements and vibrations to communicate their intent. This cautious approach helps them avoid being mistaken for prey.

Egg-Laying and Spiderlings

Once the male successfully mates with the female, she begins the process of egg-laying. The female crab spider lays her eggs in a silk sac, creating a secure and protective environment for the developing spiderlings. The egg sac location is strategically chosen to minimize threats from predators and environmental factors.

The number of eggs laid can be in the hundreds, ensuring a high survival rate for the next generation.

  • Females: Larger than males, they protect their egg sacs fiercely.
  • Males: Smaller in size, their main goal is to find and mate with females.
  • Eggs: Encased in silk sacs, they are protected by the female until they hatch.
  • Spiderlings: Newly hatched spiders face various challenges before reaching adulthood.

A quick comparison between female and male crab spiders:

Feature Female Male
Size Larger Smaller
Lifespan Longer Shorter
Role in Reproduction Egg-laying and protection Mating and courtship

In summary, the life cycle of crab spiders is an intricate dance of survival, involving complex mating rituals, secure egg-laying, and vigilant protection by females. These spiderlings then grow and continue the cycle, contributing to the fascinating world of crab spiders.

Crab Spiders and Humans

Bites and Venom

Crab spiders possess venom, which is typically more potent than most spiders, allowing them to quickly subdue prey such as bees or flies. However, they are not known to bite humans and are generally considered harmless to people. Even if a bite does occur, it does not usually cause severe reactions in humans.

Managing Crab Spider Infestations

Crab spiders usually inhabit gardens and flower beds, as they feed on insects found in these areas. They do not build webs, instead, they are ambush predators that rely on their appearance to blend in with their surroundings. To manage an infestation, consider the following points:

  • Reduce clutter, especially in attics and basements, where arachnids tend to hide.
  • Seal gaps in your home to prevent entry.
  • Regularly clean both indoor and outdoor areas.

While controlling crab spider populations may not be necessary due to their ecological importance, these measures can help prevent infestations getting out of hand.

Ecological Importance

Crab spiders play a significant role in our ecosystem as their diet mainly consists of insects, many of which are considered pests. In gardens and landscape vegetation, crab spiders help in reducing harmful insect populations and promoting a balanced environment.

Major attributes of Crab Spiders:

  • Ambush predators.
  • Do not build webs.
  • Venomous, though not usually harmful to humans.
  • Feed on insects, providing ecological benefits.

Comparison Table: Crab Spiders vs. Other Spiders

Attribute Crab Spiders Other Spiders
Web Do not build webs Most build webs
Venom More potent than most spiders Varying potency
Attitude Not aggressive, harmless to humans Varying levels of aggression and toxicity
Color Can blend with surroundings Varying colors and patterns

In conclusion, while crab spiders might seem intimidating due to their appearance and venom, they generally pose no threat to humans. Instead, they prove to be beneficial members of our ecosystem, keeping the population of harmful insects in check. By understanding their habits and characteristics, we can coexist with these fascinating arthropods in a harmonious way.

Interesting Facts

Color-Changing Abilities

Crab spiders are known for their incredible ability to change color for better camouflage. For instance, the Goldenrod crab spider can switch between white and yellow tones, depending on the flower it’s residing on. This camouflage technique helps them to:

  • Blend in
  • Ambush their prey, such as butterflies and honeybees
  • Hide from predators

Noteworthy Species

Among the different crab spider species, two stand out in particular: the Northern crab spider and the Japanese spider crab.

Northern crab spider:

Japanese spider crab:

  • Claims title of largest crab
  • Leg span of 13 feet (4 meters)
  • Average weight of around 40 pounds (16-20 kg)
  • Adoptive homes include marshes and shores
  • Known to live up to 100 years
Species Leg Span Average Weight Lifespan
Northern Crab Spider Small Lightweight Unknown
Japanese Spider Crab 13 feet(4 meters) 40 pounds (16-20 kg) 100 years

Crab spiders are invertebrates, but generally not aggressive creatures. Their natural habitats range from wild flower meadows in summer to marshes and shorelines. Some large spiders, such as giant crab spiders, pose a threat to smaller creatures like shrews. While these critters may appear intimidating, they play an essential ecological role by controlling the population of their prey, which contributes to a balanced ecosystem.

Footnotes

  1. Goldenrod Crab Spider

  2. Crab Spiders of Kentucky

  3. Northern Crab Spider 2

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Eight Spotted Crab Spider from Sumatra

 

Subject: Yellow/orange, ladybug-like spider
Location: tangkahan, north sumatra
February 20, 2016 8:58 pm
This spider was found in Tangkahan, North Sumatra, Indonesia, February 2016,, close to sea level.
Signature: matthew brealey

Crab Spider:  Platythomisus octomaculatus
Crab Spider: Platythomisus octomaculatus

Dear Matthew,
This is a Crab Spider in the family Thomisidae, identified by the length of the first two pairs of legs, and the lack of a web.  Crab Spiders do not use a web to snare prey.  We quickly found a gorgeous image on Deviant Art taken by Melvyn Yeo that is identified as an Eight Spotted Crab Spider, 
Platythomisus octomaculatus.  According to Macrophotography in Singapore:  “The Eight-Spotted Crab Spider (Platythomisus octomaculatus) has been an elusive subject to many macro photographers, appearing in the Singapore macro scene a small handful of times per year, despite being possibly the largest of all Crab Spiders (Thomisidae) in Singapore.”  According to So Much Science:  “Platythomisus octomaculatus – a rare crab spider from Borneo about 3 inches long. They sit in flowers and wait for pollinators. These guys have been known to feed on bees in captivity and Borneo has the world’s biggest and longest bees.”  Thanks for submitting this rarity to our archives.

Letter 2 – Crab Spider: Possibly Bark Crab Spider

 

primitive looking spider
Sat, May 2, 2009 at 10:58 PM
I live in the middle of a woodland forest in Mendocino County, northern California. All types of bugs find their way in my house. I promptly put them in a jar and take them back into the woods, mostly beautiful wolf spiders. But this certain spider I’ve never seen before (please see photo). It looks primitive to me, almost crab-like. Can you identify it? That would be amazing! I’d love to know what it is.
nat
Mendocino County, CA, woodlands

Crab Spider
Crab Spider

Hi Nat,
This is most certainly a Crab Spider in the family Thomisidae, and we believe it is a Bark Crab Spider in the genus Bassaniana based on a photo posted to BugGuide.  BugGuide does not list this genus in California, but the range is quite great, from coast to coast.  Like Wolf Spiders, Crab Spiders do not build snare webs.  Rather they are hunting spiders.

Letter 3 – Flattie or Wall Crab Spider from China: Family Selenopidae

 

Spider from Guizhou, China
February 24, 2010
Hi there,
This is a spider that lives on my wifes farm in Guizhou, China (northern, near Chongqing). They are everywhere. They are quite thin (flat) and manage to squeeze behind almost anything that does not move often.
Any suggestions?
Thanks
Kerry
Anchang, Guizhou, China

Flattie from China

Hi Kerry,
This is a member of the family Selenopidae, which BugGuide refers to as the Flatties, a name that is quite appropriate considering your confirming description.  According to the Biodiversity Explorer website, they are also called Wall Crab Spiders, and they are harmless.  We don’t think we will be able to provide you with a species identification.

Letter 4 – Crab Spider with a horn from South Africa

 

Subject:  What is this?
Geographic location of the bug:  Johannesburg, South Africa
Date: 03/06/2018
Time: 04:18 AM EDT
Your letter to the bugman:  Found this bug outside my garage on a wall. Looks like a horn on the back with long antennas
How you want your letter signed:  J

Crab Spider with a horn

Dear J,
This is quite an unusual looking Spider, but we have not had any luck with its identity.  We will continue to research this matter.

Update:  Cesar Crash of Insetologia posted a comment indicating this looks like a Crab Spider in the genus Tmarus, but the FlickR posting he directed us to is not from South Africa, but rather from Portugal.  Though the submitted Spider is very delicate looking for a Crab Spider, the front two pairs of legs are considerably longer than the rear two pairs, which is a good indication the family Thomisidae is correct.

Letter 5 – Flattie from Panama

 

Subject:  Id spider please
Geographic location of the bug:  Panama, western highlands 5400 ft
Date: 02/10/2020
Time: 11:26 AM EDT
Your letter to the bugman:  Hi – help id this spider who was staying still on the floor of my house in western panama highlands. About 2+ inches as in pic
How you want your letter signed:  Nancy S

Flattie, NOT Giant Crab Spider

Dear Nancy,
This is a harmless Giant Crab Spider in the family Sparassidae.  Here is an image from Flickr of a Giant Crab Spider from Panama.  We are uncertain of your species.  Giant Crab Spiders are nocturnal and they do not spin a web to snare prey.  They hunt.

Correction Courtesy of Cesar Crash: 
I think it’s a flattie, Selenops sp.

Ed. Note:  See images of a Flattie from Costa Rica on Quaoar Power Zoo.

Letter 6 – Dinner and a Date: Mating Running Crab Spiders

 

Subject:  Male running crab spider mates with female while she eats and guards an egg sac
Geographic location of the bug:  Portland, Oregon
Date: 07/15/2022
Time: 12:49 AM EDT
Your letter to the bugman:  Hi Bugman, I thought you might enjoy these photos I took of this male Philodromus sp running crab spider I came across that was trying to mate with a female who was simultaneously feeding on a fly and guarding an egg sac. I’ve never seen anything like this before.
I hope you enjoy the photos!
How you want your letter signed:  Michael Davis

Mating Running Crab Spiders

Dear Michael,
We love your photos of Running Crab Spiders mating while she simultaneously watches eggs and eats.  We have always heard that women are better than multitasking than men, which your images clearly illustrate, and this randy fellow obviously has a one track mind.  We also love that we can tag this as both Bug Love and Food Chain.

Mating Running Crab Spiders
Mating Running Crab Spiders

Authors

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  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

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  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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8 thoughts on “Crab Spider: All You Need to Know for Easy Identification and Fascinating Facts”

  1. I was browsing to identify a spider that made it home in our camping gear (not alive). We live in Southern CA and went camping a few hours north of L.A in the Sierra Nevadas last weekend. A spider that looks exactly like this was laying in the bottom of a bowl, dead. It was strange; most spiders curl up when they die, this one still has his legs sticking straight out. But it looks exactly like this one. I’ve never seen them at home, just in the mountains (that was about 5K elevation I think)

    Reply
  2. Thank you so much for posting this! I’m battling Covid right now and this was a nice surprise that definitely brightens my day.

    Reply

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