Identify a Crab Spider

Crab spiders are part of the large Thomisidae family of arachnids, with over 3,000 different kinds of crab spiders within this family. They are called crab spiders because they have uneven legs that are longer in front than in the back, which gives them the appearance and movements of a crab. Learning to identify a crab spider by its appearance and its habitat can help you to detect a Thomisidae arachnid. It can also help you know how to deal with a crab spider if you ever find one.

Steps

Identifying a Crab Spider

1. Take note of the spider’s legs. The most notable feature of a crab spider is its legs, which have longer front four legs than the back four legs. Sometimes these front legs also appear different than the other legs and are darker or hairier than their back counterparts. Like a crab, the crab spider’s front 2 legs also have incredibly strong claws which they use to grab their prey.
2. Watch the spider move. While the crab spider’s legs resemble those of a crab, it is really their gait and movements that make them most similar to their namesake. If you gently provoke a crab spider, you will see that it moves sideways like a crab on the beach. That is because their legs have something called “laterigrade leg orientation,” which means that their legs are rotated at the base, causing them to move sideways like crab.
3. Observe the color of the spider. Unlike some spider species like the brown recluse spider, the shared characteristic of crab spiders’ coloring is that it’s incredibly varied. Instead of looking for an all over color, as with the brown recluse, or the distinctive black and red coloring of a black widow spider, crab spiders are colored extravagantly to blend into their surroundings. Because crab spiders can camouflage themselves, they can be bright and vibrantly colored like a flower or a fruit, or they can be multicolored to blend into tree branches or leaves.
4. Note the size of the spider. With over 3,000 types of crab spiders, assigning a standard size to this type of spider is difficult. However, the vast majority of these species range from about 4 - 10 mm (which is the length of the body not including the legs). The female crab spiders are always larger than the males, especially when they are storing hundreds of egg sacs, and some male crab spiders are only 1/4 to 1/3 the size of their female counterparts. You should also look at the size and shape of the spider’s abdomen, as crab spiders typically have much more bulbous and round abdomens than other spider species.
5. Look at the spider’s eyes. While the prospect of getting close enough to a spider to check out its eyes can be unnerving to some, crab spiders have distinct eyes. Unlike other insects, spiders have eight eyes that are round and smooth instead of two compound eyes that have numerous surfaces like the outside of a golf ball. Crab spiders normally have two big front eyes and have excellent eyesight. The most common species of crab spiders are brightly colored around these two front eyes, or they have a noticeable ridge below these eyes called a “clypeal carina.”

Recognizing Crab Spider Habitats

1. Find out if crab spiders live in your area. With over 3,000 species of crab spiders, there is a fairly large range of climate zones that these spiders can withstand. While a few sighting of crab spiders have been noted in most parts of the world, they are most commonly found in:
   • Northwest Europe
   • Northern and eastern Australia
   • North America
2. Know where to look for crab spiders. If you live in an area where crab spiders are commonly found, the next step in identifying a crab spider is to recognize their preferred environments. Because crab spiders hunt by blending in with their surroundings, they will make a home wherever they blend in the best. While these habitats can vary depending on the specific species of crab spider, they most commonly make nests in:
   • Bunches of fruit
   • The leaves of plants
   • Thickets of grass
   • Flowers, especially brightly colored varieties
   • Pollen-producing plants
3. Watch how the spider hunts. Crab spiders are considered a hunter spider; however, the vast majority of crab spiders are not active hunters. This means that instead of actively pursuing prey, most crab spiders sit camouflaged in their nest for days or weeks at a time until an unsuspecting prey wanders too close. The clawed front legs of the crab spider are incredibly strong, and they use the additional length of these legs to reach out and grab insects. They then pull their prey in with their front legs and inject them with immobilizing venom, rarely moving their body or shorter back legs at all while hunting.
4. Note how the spider behaves. Unlike some other spider species, the crab spider is a non-aggressive spider. Crab spiders are not only passive while hunting, they are also incredibly timid and fearful of predators. Their uneven leg lengths make them fairly uncoordinated in comparison to other arachnids, which can leave them vulnerable to prey. Rather than attacking a predator, crab spiders will flee to the other side of their nest or abandon their home completely if they spot a predator nearby.
5. Search for any egg sacs. Crab spiders are unique in that they do not create webs like other species. Instead, crab spiders lay their eggs on whatever surface they’ve camouflaged themselves with, fastening the eggs to the surface with their silk. If you see any silken egg sacs that appear flat and are joined at the center, you most likely have identified a crab spider nest. Just keep in mind that female crab spiders will commonly remain near these egg sacs in order to protect them from predators, including you!

Handling Crab Spiders in your Area

1. Identify a crab spider bite. Spider bites from any arachnid family look like two distinct puncture marks. These puncture marks are caused by the hollow fangs that all spiders use to inject venom into their prey. A crab spider’s bite is not dangerous to humans because the venom is not potent enough and most crab spiders are not big enough to break the skin with their fangs. However, some species like the giant crab spider (Olios giganteus) are big enough to puncture the skin, and the bite from the larger crab species is said to be pretty painful.
2. Manage crab spiders when found indoors. Due to the crab spider’s preferred habitat, it is very unlikely to find this type of spider inside. If you do happen to find one inside though (and you’re not too scared!), it is recommended that you gently capture the spider by scooting it into a cup, covering it, and releasing it outside. They are not harmful to humans and are a great way to control the population of other insects like bees, wasps, mosquitoes, and flies. Some other tips for reducing the number of crab spiders in your home include:
   • Check all flowers and plants for crab spiders before you bring them inside, especially flowers recently cut from a garden.
   • Capture and discard or relocate individual spiders that have wandered inside because they reproduce rapidly.
   • Remove or regularly inspect any potted plants and flowers inside the home as this is the most likely spot a crab spider would reside in indoors.
3. Cope with crab spiders outdoors. Crab spiders are harmless to humans, so eradicating them from your outdoor area is not advised unless there is an extreme infestation. Try to see the crab spider as helping to keep your home free of bees, wasps, mosquitoes, flies, and other pesky insects. However, if you prefer to reduce the number of crab spiders in your outdoor area, you can:
   • Remove all piles of plant debris, like piles of kindling, grass clippings, or mulch.
   • Keep grassy areas near your home cut short.
   • Avoid planting pollen-producing plants.
   • Periodically remove crab spider nests with a broom or a hard spray of water.

Warnings

• If you are bitten by a spider (crab spider species or otherwise) and the area surrounding the two puncture marks becomes red, painful, or swollen, seek medical attention. If you can, bring the spider with you or try to remember what it looked like so you can describe it to the doctor.

Related Articles

• Identify a Nursery Web Spider
• Identify a Hobo Spider
• Keep Spiders As Pets

Sources and Citations

See also

• Make Your Food Bear Safe when Camping
• Stop a Bee from Stinging You
• Avoid a Rattlesnake Attack
• Identify Insect Bites
• Escape from Dangerous Forest Animals
• Kill a Tick
• Avoid Mosquito Bites
• Avoid Bee or Wasp Stings
• Identify a Trapdoor Spider
• Survive a Bear Attack

Read more ...

What links here

• Identify a Barn Spider
• Identify a Nursery Web Spider