Crab spiders are a common type of spider found throughout the world. They get their name from their crab-like appearance and sideways walk. Despite their unusual look, crab spiders are not considered dangerous or harmful to humans. In this article, we’ll take a closer look at crab spiders to understand if they pose any risks.
Quick Answers
Crab spiders are not aggressive – They do not attack humans unless provoked. Their venom is not considered medically significant to humans. Crab spiders help control insect populations. They are an important part of the ecosystem.
Appearance and Identification
Crab spiders belong to the family Thomisidae. There are over 2,000 species of crab spiders throughout the world. They are found on every continent except Antarctica.
Crab spiders have a flat, wide body and legs that extend out to the side like a crab. Their front two legs are usually larger than the back legs. They range in size from only a few millimeters to over 2 inches legspan. Their coloring can be white, yellow, green, brown or gray. This allows them to camouflage with their surroundings.
Here are some ways to identify crab spiders:
- Flattened body shape, wider than it is tall
- Legs extend out to the sides
- Front two legs larger than hind legs
- Ability to walk sideways or backwards
- Camouflaged coloring
- Often found in flowers and foliage
Crab spiders have eight eyes, with two large front-facing eyes. This gives them excellent eyesight to spot prey. The positioning of their eyes allows them to see in all directions.
Behavior and Habits
Crab spiders are ambush predators. They wait camouflaged in flowers and foliage for prey to come to them. Then they quickly strike, injecting venom to immobilize their prey. They do not use webs to catch food.
Some unique behaviors and habits of crab spiders include:
- Camouflaging themselves to blend in with surroundings
- Lying in wait for prey
- Swift ambush attacks
- Ability to walk sideways and backwards
- Nocturnal hunting
- Seasonal migration
Crab spiders are most active during spring and summer months. In cold climates, they migrate to sheltered areas and become inactive during winter. They are primarily nocturnal hunters.
Crab spiders do not build webs for catching prey. They rely solely on stealth and ambush tactics. Some species can change color over a period of days to better match their surroundings.
Diet and Hunting
Crab spiders are carnivorous and feed on a variety of small insects and other arthropods. Common prey includes:
- Flies
- Bees
- Butterflies
- Mosquitoes
- Beetles
- Moths
- Caterpillars
- Grasshoppers
- Ants
- Aphids
To hunt, crab spiders wait perfectly still in flowers and foliage for unsuspecting prey to land or crawl within striking range. Then they use their front legs to grasp prey and swiftly bite with their fangs to inject venom. The venom acts rapidly to paralyze and subdue prey.
Crab spiders are able to tackle prey much larger than themselves. Their diet is opportunistic based on what insects are available in their habitat.
Venom and Bites
Crab spiders do have venom that they use to subdue prey. However, their venom is not considered medically significant to humans. While crab spider bites can happen on rare occasions, they do not cause serious harm.
Here are some key facts about crab spider venom and bites:
- Venom is used primarily to paralyze arthropod prey
- Bites may cause mild pain and swelling in sensitive individuals
- Medical treatment is typically not required
- No records of life-threatening reactions to bites
- They rarely bite humans unless pressed against skin
- Non-aggressive spiders, not prone to defending themselves
If bitten, cleaning the bite area with soap and water is recommended. Applying ice and taking antihistamine can help relieve mild symptoms. Seek medical care if severe reaction occurs.
Population and Distribution
There are over 2,000 known species of crab spiders found around the world. They inhabit every continent except Antarctica. Below are some key facts about crab spider populations and distribution:
- Found on all continents except Antarctica
- Thrive in tropical, subtropical and temperate regions
- Most diverse populations in South America and Asia
- Over 560 species in North America
- Common across Europe, Africa and Australia
- Live in wide range of habitats from forests to grasslands
Crab spiders are adaptable creatures and can be found in many types of environments. They are common in areas that provide foliage, vegetation and flowering plants for camouflage and access to prey.
Habitat and Ecosystem Role
Crab spiders inhabit a diverse array of natural and human-made habitats. Anywhere that provides adequate hiding spots and prey availability can support crab spider populations. Some prime habitats include:
- Meadows
- Woodlands
- Grasslands
- Agricultural areas
- Gardens
- Backyards
- Orchards
- Fields
- Forests
Crab spiders play an important role in their ecosystem. As predators of insects and arthropods, they help naturally regulate populations of species that can spread disease or become agricultural pests if left unchecked. Crab spiders are an integral part of the food web.
Interaction with Humans
Crab spiders and humans frequently encounter each other, but crab spiders pose no risks to people. They may sometimes wander indoors, but are not adapted to live inside. Here are some key facts about crab spiders and humans:
- Non-aggressive, shy spiders that avoid humans
- Venom has no medical significance to humans
- Bites are very rare and only cause mild, localized reaction
- Help control insect pests like flies, mosquitoes and moths
- Do not infest homes or damage property
- Important part of the ecosystem and food web
While startling if they suddenly appear, crab spiders should not be killed as they provide free pest control services. Simply transport them gently back outside if found indoors. They play a valuable role in nature.
Threats and Predators
While crab spiders may seem menacing to insects, they also face their own set of threats from predators. Common crab spider predators include:
- Insects – predatory wasps, assassin bugs, praying mantises
- Arachnids – lynx spiders, jumping spiders
- Amphibians – frogs, toads
- Reptiles – lizards, snakes
- Birds – shrikes, mockingbirds, warblers
- Rodents – mice, shrews
Crab spiders employ camouflage, concealment, speedy retreats, and threat displays like rearing up on legs to avoid becoming prey. However, they occupy an important middle level in the food chain, serving as both predator and prey.
Reproduction and Life Cycle
Crab spiders undergo a simple metamorphosis with an egg, spiderling, and adult stage. The life cycle spans approximately one year for most species. Here are key facts about their reproduction and development:
- Males attract females by waving front legs
- During mating, male crab spiders transfer sperm to female’s genital opening using pedipalps
- Females lay 20 to several hundred eggs encased in silk egg sac
- Females guard the egg sacs by carrying them in their jaws
- Spiderlings hatch after 10 to 30 days
- Spiderlings molt and mature to adulthood in 2 to 6 months
- Adults live for about 1 year
Interestingly, female crab spiders can store sperm and produce multiple egg sacs from one mating. The egg sacs are often cleverly camouflaged or hidden during the maternal care period.
Taxonomy and Classification
Crab spiders belong to the arachnid order Araneae which contains over 47,000 species of spiders. Here is their complete scientific classification:
- Kingdom: Animalia
- Phylum: Arthropoda
- Subphylum: Chelicerata
- Class: Arachnida
- Order: Araneae
- Family: Thomisidae
Within the Thomisidae family, there are 175 genera containing over 2,000 species of crab spiders. Some notable crab spider genera include:
- Thomisus – flower or flowering crab spiders
- Misumena – flower crab spiders
- Xysticus – ground crab spiders
- Ozyptila – woodlouse hunter spiders
- Coriarachne – flat bodied crab spiders
This classification helps differentiate crab spiders from other spider families like jumping spiders (Salticidae) and wolf spiders (Lycosidae). Taxonomy remains a dynamic field as scientists continue documenting Earth’s biodiversity.
Conclusion
In summary, crab spiders are not harmful to humans. They have unique crab-like features and behaviors, but their venom is mild and non-threatening. Crab spiders are timid creatures that play an important ecological role as insect predators. They may look intimidating, but in reality crab spiders are harmless companions in backyards and gardens around the world.
