Crab spiders (family Thomisidae) are common outdoor inhabitants that sometimes wander into homes. These arachnids are ambush predators, meaning they do not spin sticky webs to catch prey. They typically enter structures while pursuing other insects or searching for shelter, often near windows and doors. Crab spiders are not considered dangerous to humans, which allows removal efforts to focus on non-toxic methods.
Identifying the Crab Spider and Assessing Risk
Identifying a crab spider is straightforward due to its distinctive physical features. They have a flattened body shape and a pair of long, robust front legs held out like a crab’s claws. This posture allows them to quickly grasp prey, and they can move sideways or backward, contributing to their crab-like appearance. Their coloration is highly variable, often ranging from white and yellow to green or brown, which allows them to camouflage perfectly on flowers or foliage.
Most crab spiders are small, typically measuring between 4 and 10 millimeters in body length. While they possess venom to paralyze insects, it is not medically significant to humans. A bite is extremely rare and would likely result only in minor, localized irritation comparable to a slight pinprick.
Immediate Non-Chemical Removal Techniques
For any crab spider visible inside your home, physical removal is the simplest approach. The classic method involves placing a glass cup over the spider, sliding a stiff piece of paper underneath, and releasing the animal safely outside. A quick alternative is using a vacuum cleaner with a hose attachment for hands-free removal. After vacuuming, immediately empty the canister or dispose of the sealed bag outside to prevent escape.
Sticky traps can be placed in undisturbed indoor areas, such as along baseboards or behind furniture, capturing the spider on a strong adhesive. On the exterior of the home, a strong blast of water from a garden hose can dislodge any spiders or insects congregating on entry points.
Long-Term Prevention and Exclusion Strategies
Achieving a lasting solution requires modifying the home environment to make it unattractive to crab spiders and their prey. Begin by meticulously sealing any structural gaps, as spiders can enter through extremely small openings. Use silicone caulk to seal cracks around window frames, door casings, and utility line entry points.
Exclusion efforts should also focus on modifying the immediate outdoor habitat surrounding the foundation. Trim back vegetation touching the house, as these act as bridges for spiders to access the structure. Reducing yard clutter, such as piles of wood or leaf litter, eliminates damp, dark hiding spots preferred by crab spiders.
Controlling the spiders’ food source is a highly effective prevention strategy. Minimize household pests by cleaning up food spills and using sealed containers for pantry items. Outside, consider switching bright exterior lights near doorways to yellow sodium vapor bulbs, which are less appealing to the flying insects that serve as prey.
For persistent issues, a residual insecticide can be applied to the home’s exterior perimeter as a final measure. Apply this product in a band approximately three to four feet up the foundation and three to four feet out onto the ground. This creates a chemical barrier that deters spiders from entering the home, but it must be used strictly according to the product label instructions.