Crab spiders are part of the large Thomsidae family of arachnids, with more than 3,000 types of crab spiders, having this name because they have legs of different sizes; those in the front are larger than the ones in the back, mimicking the movement of crabs. Learning to identify this type of spider by appearance and habitat can help detect and deal with an arachnid from the Thomsidae family when you encounter one.
Method 1 of 3: Identifying a Crab Spider
Step 1. Notice what the spider's legs look like
The most notable aspect of this type of spider is its legs, which are longer in front than behind (both sides have four legs). Sometimes the front legs look different from the others, being darker in color or more hairy than the hind legs. Like a crab, the two forward legs have very strong claws used to capture their prey.
Step 2. Observe the spider's movement
While the legs of the crab spider resemble a crab, it is the movements and gait that make them more similar to the crustacean. By carefully teasing this type of spider, you'll notice that it moves sideways, like a crab on a beach. This is due to the rotation of the legs, which occurs at the base, causing lateral movement similar to those of crabs.
Step 3. Note the color of the spider
Unlike some species of arachnids, such as the brown spider, the shared characteristic in relation to the coloration of crab spiders is the distinct coloration. Instead of looking for a common color, such as the brown or the red and black of a black widow, arachnids in this family show exotic colorations that blend in with their surroundings. As they camouflage, they can look bright and colorful, like a flower or fruit, showing various colors and “blending” with tree branches or leaves.
Step 4. Note the size of the spider
With over 3,000 species of Thomsidae spiders, it is nearly impossible to determine a standard size for this arachnid. However, the vast majority of species range from 4 to 10 mm (the size of the body, not including the legs). Females are almost always larger than males, especially when storing hundreds of egg bags. Also, some males are only 1/4 to 1/3 the size of their females. Another option is to analyze the size and shape of the spider's abdomen, as arachnids of this type generally have rounder, more robust abdomens than other species.
Step 5. Analyze the spider's eyes
Getting close to a spider to see its eyes is dangerous for some, but you can see how distinct they are; unlike other insects, they have eight round, soft eyes rather than two eyes made up of multiple surfaces, like the outside of a golf ball. Typically, crab spiders have two large frontal eyes and very good eyesight. The most common species in the Thomsidae family has glowing eyes around the two largest, or an easy-to-see crest just below them.
Method 2 of 3: Recognizing Crab Spider Habitats
Step 1. Find out if this species lives in your region
With more than 3,000 species, there is a wide range of climate zones that this type of spider supports and, although they have been found almost everywhere in the world, they are easier to find:
- In northeastern Europe.
- In North and East Australia.
- In North America.
Step 2. Know where to look for crab spiders
When living in a place where these spiders are easily found, the next step is to identify the environments where they settle. As they use “camouflage” to blend in with their surroundings, they will nest in places where they can be well hidden. Although habitats can vary depending on the species of spiders, it is more common for them to install nests in:
- Lots of fruit.
- Plant leaves.
- Thickets of grass.
- Flowers, especially colored ones.
- Plants that produce pollen.
Step 3. Watch how the spider hunts
Crab spiders are considered hunters; however, the vast majority of them are not active hunters. This means that, instead of chasing prey, they prefer to remain camouflaged in their nests for days or weeks until the “food” walks closer to them. The claws they have on the front of their paws are very strong and long, allowing them to catch insects with some ease, pulling and injecting venom that immobilize them. This is all done without moving their bodies and smaller hind legs.
Step 4. Note the spider's behavior
Unlike other species, the crab is not aggressive; not only are they passive when hunting, they are also fearful of predators and “shy”. The different size of their legs makes their movement quite uncoordinated in relation to other arachnids, making them very susceptible to their predators. Instead of attacking a possible predator, they prefer to flee to the other side of the nest or even abandon it when they detect a threat.
Step 5. Check for egg bags
Crab spiders are unique in that they do not create webs like other species; instead, they lay their eggs on whatever surface they camouflage on, pinning the eggs to the surface using silk. When you find silk-covered eggs, with a flat appearance and connected at the center, it is probably a crab spider's nest. Remember that females will stay close to these bags to protect them from predators, including you!
Method 3 of 3: Dealing with Thomsidae Spiders in Your Area
Step 1. Identify a crab spider bite
The bites of any arachnid family are shaped like two needles, side by side, caused by the fangs that all spiders use to inject venom into their prey. The crab does not have a venom strong enough to cause problems in humans, and it rarely breaks the skin with its prey. However, there are some species in this family, such as the giant crab spider (Olios giganteus), which can pierce the skin, in addition to causing a lot of pain.
Step 2. Know what to do when encountering this type of spider
Due to the preferred habitat of crab spiders, it is rare to find it indoors; should this happen – and you don't get too scared – it is recommended that it be carefully captured by holding it in a cup, covering it and releasing it outside the house. They are not dangerous to humans and even help to reduce the number of wasps, mosquitoes, mosquitoes and bees in the surroundings. Other tips to reduce the amount of spiders of this type in your home are:
- Check all flowers and plants. See if they contain spiders of this type before putting them indoors, especially on freshly cut flowers in a garden.
- Capture and discard or place them elsewhere on entry as they reproduce quickly.
- Remove or analyze all plants and flowers indoors, as these are the most suitable places for a crab spider's nest.
Step 3. Deal with crab spiders outside the house
As they are not harmful to humans, it is advised that they are not eradicated, unless the infestation is very large. Remember that this species of spider helps keep your home free from bees, wasps, mosquitoes, mosquitoes, and many other insects; however, if you prefer to reduce the number of spiders outside the house, do the following:
- Remove all stacked plant debris such as leaves, sticks, and cut grass.
- Grassy areas near your home should be kept very short.
- Avoid plants that produce pollen.
- Remove spider nests regularly, using a broom or a strong jet of water.