tuberculated crab spider

(Tmarus angulatus)

Conservation Status
tuberculated crab spider
Photo by Alfredo Colon
  IUCN Red List

not listed

     
  NatureServe

NNR - Unranked

     
  Minnesota

not listed

     
           
           
           
           
           
           
           
 
Description
 
 

Tuberculated crab spider is a medium-sized spider. It occurs across the United States and southern Canada. It is common east of the Great Plains and it occurs in California but is otherwise rare in the west. It is common in Minnesota. It is found on stems and twigs of plants in fields, meadows, and gardens.

Females are 316 to ¼ (4.5 to 7.0 mm) in length with a legspan of to (10 to 15 mm). Males are much smaller, to 316 (3 to 5 mm) in length.

The front part of the body (cephalothorax) is greatly elongated. strongly convex above, and smoothly rounded on the sides. It is dark brown with a tan stripe in the middle, scattered black spots and light areas, and a few erect hairs. There are eight eyes arranged in two curved rows of four. The lateral eyes are larger than the median eyes and are on separate large raised bumps (tubercles). The posterior median eyes (PMEs) are larger than the anterior median eyes (AMEs). The median ocular area (MOA), the area defined by the middle four eyes, is wider than long. The facial plate above the mouth (clypeus) is strongly sloping, nearly vertical.

The abdomen is longer than wide, broadly angled beyond the middle on the lateral margins, and sharply angled at the rear. This is the feature that gives the spider the first part an alternate common name, angled crab spider. The upper surface is dull brown mottled with white specks. There is a pale longitudinal stripe in the middle and there are rows of dark chevrons toward the rear. The abdomen is highest in the rear and there is a conspicuous, large tubercle near the end. The tubercle is much larger on the female than on the male. This is the feature that gives the spider the first part of its common name. When viewed from the side the spider looks like a bud or the stump of a broken leaf stalk (petiole).

The legs are pale brown and are densely speckled with black. The first two pairs of legs are much longer than the third and fourth pairs, and are held out forward or to the side. When held to the side (laterigrade), the spider is able to move quickly sideways, like a crab. This is the feature that gives the family its common name. The last leg segment (tarsus) on each leg has two claws at the end and just a single long sensory hair (trichobothrium). The claws are not visible to the naked eye. The tarsi on the first and second pairs of legs do not have a brush of hairs (scopula) on the underside, and there is no tuft of hairs (claw tuft) at the end on any leg.

 
     
 

Size

 
 

Female Body Length: 316 to ¼ (4.5 to 7.0 mm)

Male Body Length: to 316 (3 to 5 mm)

Legspan: to (10 to 15 mm)

 
     
 

Similar Species

 
     
     
 
Habitat
 
 

Fields, meadows, and gardens

 
     
 
Biology
 
 

Season

 
 

 

 
     
 

Behavior

 
 

When hunting, the spider often clings to a stem or twig with its first and second pairs of legs straight out in front and its third pair clasping the stem or twig. In this position, with its cryptic coloration and uniquely shaped abdomen, it is well camouflaged and difficult to see.

 
     
 

Life Cycle

 
 

Spiderlings overwinter in the second-to-last development stage (penultimate instar).

 
     
 

Food

 
 

 

 
     
 
Distribution
 
 

Distribution Map

 

Sources

24, 29, 30, 82.

 
  1/5/2022      
         
 

Occurrence

 
 

 

 
         
 
Taxonomy
 
  Class Arachnida (arachnids)  
 

Order

Araneae (spiders)  
 

Suborder

Araneomorphae (typical spiders)  
  Infraorder Entelegynae (entelegyne spiders)  
 

Superfamily

Thomisoidea (crab and running crab spiders)  
 

Family

Thomisidae (crab spiders)  
 

Genus

Tmarus (octopus spiders)  
       
 

Synonyms

 
 

Philodromus inquisitor

Thomisus angulatus

Thomisus caudatus

Tmarus caudatus

Tmarus caudatus

 
       
 

Common Names

 
 

angled crab spider

tuberculated crab spider

 

 

 

 

 

 

 

 

 

Glossary

Carapace

The hard, upper (dorsal), shell-like covering (exoskeleton) of the body or at least the thorax of many arthropods and of turtles and tortoises. On crustaceans, it covers the cephalothorax. On spiders, the top of the cephalothorax made from a series of fused sclerites.

 

Cephalothorax

The front part of the body of various arthropods, composed of the head region and the thoracic area fused together. Eyes, legs, and antennae are attached to this part.

 

Clypeus

On insects, a hardened plate on the face above the upper lip (labrum).

 

Instar

The developmental stage of arthropods between each molt; in insects, the developmental stage of the larvae or nymph.

 

Petiole

The stalk of a leaf blade or compound leaf that attaches the leaf blade to the stem.

On plants: The stalk of a leaf blade or compound leaf that attaches the leaf blade to the stem. On ants and wasps: The basal stalk of the abdomen.

 

Tarsus

On insects, the last two to five subdivisions of the leg, attached to the tibia; the foot. On spiders, the last segment of the leg. Plural: tarsi.

 

Tubercle

On plants and animals: a small, rounded, raised projection on the surface. On insects and spiders: a low, small, usually rounded, knob-like projection. On slugs: raised areas of skin between grooves covering the body.

 

 

 

 
 
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Alfredo Colon

 
    tuberculated crab spider   tuberculated crab spider  
           
    tuberculated crab spider   tuberculated crab spider  
           
 
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  Alfredo Colon
6/1/2021

Location: Woodbury, MN

tuberculated crab spider  
  Alfredo Colon
8/2/2019

Location: Woodbury, MN

tuberculated crab spider  
           
 
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Created: 1/5/2022

Last Updated:

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