Are Crab Spiders Poisonous? Facts on Identification & Bites

Are crab spiders poisonous? It’s an important question to answer. Crab spiders belong to the family Thomisidae. Usually, they aren’t dangerous to us humans. However, a few species may cause minor to serious skin irritations. Hence, it’s essential to be aware of their habits and habitats before handling them. To be on the safe side, it’s best to take precautions when dealing with crab spiders.


Types of Crab Spiders

Crab spiders, or Thomisidae, come in all shapes, sizes, and colors. In forests, deserts, and other natural areas, they are quite common. Amazingly, they can camouflage, making them hard to spot!

Let’s explore the different types of crab spiders and if they are venomous:


Thomisidae (Flower or Crab Spiders)

Thomisidae, also known as crab spiders, is a family of spiders found all around the world. They are commonly seen in temperate regions of the Northern Hemisphere. These spiders have short bodies and elongated legs, and come in various colors.

Approximately 2000 species belong to this family. Not all of them contain venom that is harmful to humans. Crab spiders hunt their prey instead of using webs or other methods, like jumping spiders. They prefer dry habitats, like shady spots near trees or flowers. These can be found in gardens or wooded regions that are left undisturbed for long periods of time.

Unlike many other spider species, adults and juveniles of crab spiders can be seen in the same place during summer months. This is because adults look after their offspring until they reach adulthood. The young adults molt several times before leaving to lay eggs in other places.

Crab spiders don’t use webbing. Instead, they ambush their prey with poison from their chelicerae (frontmost sections) and bite it with their fang-like structures near their pedipalps and cephalothorax (spider’s head).


Philodromidae (Running Crab Spiders)

Philodromidae, or running crab spiders, are a well known family. They have short legs and flat soles that help them move fast on flat surfaces. There are around 520 species worldwide and 64 in the United States.

Most belong to the genera Tibellus, Diaea, Phrynarachne, Xysticus and Philodromus. Others are Ebo and Trite. These spiders measure 5 to 8 millimeters in length, making them an intermediate size.

They have small oval-shaped bodies with large eyes, ranging from yellow to white. Most species have brownish-yellow bodies with white markings or black stripes on their abdomen. Their first pair of legs is longer than the other four. This helps them see potential prey.

Female crab spiders can hunt both insects and arachnids. They also have a special respiratory system made up of book lungs and tracheae. Males rarely hunt, so they have weak hunting structures or none at all.

When threatened, they can raise their front two pairs of legs. If disturbed, they may bite. So if dealing with home infestations, be careful when in contact.


Dysderidae (Wood or Cellar Spiders)

The Dysderidae, or Wood and Cellar spiders (Dysdera crocata), are a large family of spiders. They get their name from living in dark, damp places like in cellars, attics, barns and moist woodlands. They also lurk outdoors, under logs and stones, or even in your garden! These spiders are usually brown, but can also come in yellow and green shades.

Wood and Cellar spiders can grow to 1/3 an inch long. They have six eyes arranged in a semi-circle, like a horseshoe. These spiders actively hunt their prey, but they also wait patiently for it. They feed on bees, flies, moths, or beetles.

Wood and Cellar spiders have venom, which they use to paralyze their prey. It is harmless against humans, but they may bite when disturbed. So take caution when handling them. Respect these arachnids as you would any other.


Are Crab Spiders Poisonous?

Crab spiders – a family of arachnids found globally. Although varying in shape and size, they are easily recognized by their elongated front legs. Generally considered harmless, they may be venomous.

Now, let’s explore the facts of these spiders and their potential toxicity.


Thomisidae (Flower or Crab Spiders)

The Thomisidae family, otherwise known as flower or crab spiders, consists of roughly 1300 species. They typically dwell in webs across Europe, Africa, Asia, and North America. These spiders are identified by their forward appendages pointing toward their body.

Are they venomous? In most cases, their venom is not considered medically significant for humans and cats, and non-venomous for dogs. Yet, some bites may cause minor irritation or swelling in certain animals. Also, certain species do not have venom at all.

Thomisids are mostly harmless to people and large animals. Except for a few cases, where defensive glands may spray a pheromone-like liquid when disturbed. If inhaled, this could cause an allergic reaction with minor respiratory issues, depending on sensitivity. Furthermore, female Thomisids may bite defensively if feeling uncomfortable. Such bites result in local swelling, depending on individual sensitivity. These reactions are mild and last a few minutes to several hours.


Philodromidae (Running Crab Spiders)

Philodromidae, known as running crab spiders, are the largest and most diverse family of crabs. They are found on all continents. These spiders have flat bodies with long legs standing horizontally. They range from 0.2 to 3.2 mm (0.009 to 0.126 inches).

They feed on insects and can also scavenge leftovers or nectar from flowers. Their main defense is camouflage. But, if they feel disturbed or threatened, some species have venom that can be harmful. So, it’s best to use caution when handling these spiders.


Dysderidae (Wood or Cellar Spiders)

The Dysderidae family, otherwise known as woodlouse spiders, are a large species of crab spiders. About 1,000 species exist globally. Most tend to live on the ground or within soil and hunt at night. They inject venom into their prey, paralyzing then consuming them.

This family is split into two subfamilies – land-dwelling and freshwater-dwelling. Their sizes range from 0.5 to 2 inches (1 to 5 centimeters). Land-dwellers have a variety of color patterns: light brown, grayish-black, and some with reddish patterns.

Woodlouse spiders rarely bite humans, but caution should be taken. The Mediterranean thinlegged crab spider has a powerful venom that can cause serious medical problems. It’s best to avoid them, especially when outdoors or near freshwater sources.



Reviewing sources reveals some crab spider species have venom which causes serious reactions in humans. These may include swelling, pain, rashes and fever.

Avoid these spiders when possible and seek medical help if bitten.

Though many crab spider species are not considered dangerous, there’s not enough info to conclude all species lack the ability to harm humans. Best to be careful when handling any spider. If bitten by a potentially dangerous crab spider, seek medical attention immediately.


Frequently Asked Questions

Q: Are Crab Spiders Poisonous?

A: No, crab spiders are not poisonous. They do not have any venom and they will not bite humans. They are harmless to humans.

Q: What do Crab Spiders Eat?

A: Crab spiders mainly eat other insects such as flies, bees, and moths. They also feed on small spiders and occasionally other small invertebrates.

Q: How Big do Crab Spiders Grow?

A: Crab spiders can grow up to 3mm in length. They have long legs and small bodies.