Crab Spiders

Description

Spiders of this family do not spin webs for hunting, only for travel or reproduction. Most are ambush hunters, and the best known use known as flower crab spiders because they use camouflage to hide on flowers and eat pollinators. Some wait on other plant parts or in the open, and some are even active hunters.

The name crab spider comes from their elongated first and second legs, giving a crablike appearance. While many spiders have the capacity to change color based on their diet, some crab spiders are apparently able to change their color for the specific purpose of camouflage with their surroundings.

Species

Mecaphesa asperata

"Northern Crab Spider"

Description

This spider is able to change its coloration noticeably and may be green or yellow overall. However, it is distinguished by a pair of dark vertical stripes on its dorsal prosoma and, usually, reddish coloration on the middle parts of its elongated first and second legs. The opisthosoma may be a brighter yellow with mirrored reddish markings.

Notes

This spider is widely found in North America and can commonly be seen in wait on flowers or leaves.

Images of Northern Crab Spider

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Yellow Mecaphesa asperata waiting for prey on a flower, with a very small ant approaching. Note the faint dark stripes on the opisthosoma.
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The same M. asperata pictured from the side. While the legs are uniformly colored, the leg spines and opisthosoma markings give this species away.
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A greenish northern crab spider on a sunflower. This species can take several days to change color, so this specimen may be in the process of improving its camouflage.

Mecaphesa celer

"Swift Crab Spider"

Description

This spider is highly variable in coloration, and displays extreme sexual size dimorphism, with females being up to twice the size of males. The first two pairs of legs are significantly longer than the last two pairs. Legs and body are covered in stiff black spines (setae). Typically this species ranges from pale green to yellow to white in color. Opisthosoma markings are variable but typically appear as symmetrical pairs of dark spots or triangles.

Images of Swift Crab Spider

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A very small, perhaps juvenile crab spider pictured through a jeweller's hand lens. This specimen is likely the Swift Crab Spider based on the opisthosoma patterning, but members of Mecaphesa can be difficult to identify due to high variation.
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More of the same M. celer specimen, a dark yellow but partially transparent crab spider with distinct black setae (often called bristles or hairs) all over.

Xysticus Ferox

"Tan Ground Crab Spider"

Description

Although females are indeed pale tan and distinguished from other Xysticus species in that way, males tend to be quite dark and look similar to other members of the genus. Legs and opisthosoma have many dark markings. This species has pale lines crossing the opisthosoma but otherwise smaller tan markings than the very similar (in males) X. elegans. This species bears a dark spot toward the rear of the prosoma, characteristic of the genus, as well as slight pale outlines on the raised central portion of the prosoma.

Images of Tan Ground Crab Spider

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This adult male Xysticus ferox was spotted crossing a paved path at night and quickly put up a defensive posture upon approach. Its first and second legs are raised, but it is missing the first and fourth legs on the right side.
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The same specimen photographed from behind for a clearer view of its markings. Although this specimen has large tan patterning on its opisthosoma, the paleness of the rear legs' lower sections and the lack of a large tan prosoma marking indicate that other Xysticus species are unlikely.

Unidentified Crab Spiders

Images of Unidentified Crab Spiders

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A crab spider seen in the Blue Ridge Mountains. Unfortunately I wasn't abel to get any high quality photos of this spider. Its red, yellow, and green coloration is unusual, but I suspect it is a member of genus Mecaphesa.
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The same crab spider pictured previously. Some indistinct markings can be seen on the opisthosoma, as well as darker bands on either side of the prosoma which are common among Thomisidae.