This month's "bug"

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Bug of the Month: Woodlouse hunter

Common name: Woodlouse hunter

Latin name: Dysdera crocata C.L. Koch 1838

Kingdom Animalia
   Phylum Arthropoda
      Class Arachnida
         Order Araneae
            Family Dysderidae


Top view of a male woodlouse hunter (dysdera crocata)
Spiders in general

Like insects, spiders are in the Phylum Arthropoda. Unlike insects, however, spiders have eight legs (plus two leg-like "pedipalps" arising from behind the jaws), no antennae, and their body is divided into only two parts (the head and thorax are combined into the "cephalothorax"). Spiders are grouped in the class Arachnida with closely related orders such as mites, scorpions, and daddy-longlegs. Other distinctive features of spiders include eight simple eyes (typically), large jaws with fangs and poison glands, breathing organs on the underside of the abdomen known as "book lungs," and silk producing organs at the posterior end of the abdomen called "spinnerets."

photo of pedipalps of male and female woodlouse hunters

How to identify woodlouse hunters
Woodlouse hunters are generally 9-15mm long (excluding legs). Unlike most spiders, they have only six eyes, grouped closely together. Their jaws are relatively large, with long fangs for piercing through the hard armor of their prey (sowbugs and sometimes beetles). The body of the woodlouse hunter is generally smooth, not hairy. The cephalothorax (front segment) is reddish orange, and the abdomen is usually tan or grayish white. Males are smaller in size, and their genitalia are visible on the ends of the pedipalps.

Where to find woodlouse hunters on the Boston Harbor Islands

Woodlouse hunters are very abundant on the islands, and are found wherever their prey (sowbugs, see below) occur. They can be found in both meadows and forests in dark, humid places such as under rocks, logs or leaf litter. In North America, woodlouse hunters are often found in urban, disturbed habitats, close to humans.

How woodlouse hunters make a living

Not surprisingly, woodlouse hunters eat woodlice! "Woodlouse" is a British term for animals we know more familiarly as sowbugs, pillbugs, roly-polies, or, more formally, as isopods. They may also eat beetles. These spiders hunt at night, actively searching out their prey. Woodlouse hunters do not build webs, but construct small, silken oval-shaped retreats. They overwinter as adults, and after mating in the spring, females deposit about 70 eggs in their retreat. When the young hatch, they stay near the mother for a short period of time.

view of the underside of a female woodlouse hunterWhere in the world woodlouse hunters occur

Woodlouse hunters and their relatives (in the family Dysderidae) are native to the western "palearctic region" which includes Europe, northern Asia, and northwestern Africa. Most species are native to areas around the Mediterranean. The woodlouse hunter however, has expanded its range with the help of humans. Like its favored prey, woodlice, which have been carried around the planet by humans in soil and ballast, the woodlouse spider is now found in most regions of the world.

To learn more about woodlouse hunters (and spiders in general)

On the web:

In print:

    Cooke, J.A.L. 1965. A contribution to the biology of the British spiders belonging to the genus Dysdera. Oikos. 16:20-25.

    Kaston, J.K. 1948. Spiders of Connecticut. State Geological and Natural History Survey. Bull. No. 70. The Peiper Press, Inc. Wallingford, CT.

    Ubick, D., P. Paquin, P.E. Cushing, and V. Roth (eds.) 2005. Spiders of North America: an identification manual. American Arachnological Society. 377 pages.