Introduction to Spider Species
The world of spider species is incredibly vast and varied, with over 48,000 species identified across the globe. Among these, some spiders have evolved remarkable adaptations that allow them to specialize in hunting particular types of prey. The woodlouse spider, scientifically known as Dysdera crocata, is a prime example of such specialization. Often referred to by common names like woodlouse hunter, sowbug hunter, sowbug killer, pillbug hunter, and slater spider, this species preys primarily on woodlice. These spiders have developed unique hunting strategies and physical traits that set them apart from other animals in their environment. By focusing on woodlice as their main prey, woodlouse spiders play a distinct role in the ecosystem, demonstrating how spider species can evolve to fill specific ecological niches.
The Woodlouse Spider
The discovery of a spider making a home in your isopod enclosure is a frightening thought for all isopod hobbyists. But did you know there is a species of spider that preys primarily upon woodlice? Yes, that’s right, the isopod nemesis is known as the woodlouse spider (Dysdera crocata and Dysdera erythrina). The spider is also known as the woodlouse hunter, sowbug hunter, sowbug killer, pillbug hunter and slater spider. All known names sound terrifying!
The woodlouse spider species is known for their impressive long, curved fangs which stand out against its relatively small size which gives the spider a formidable appearance. It is a tawny orange to dark-red colouring (a cuter nickname for this spider is the baked bean spider) with a shined exo-skeleton and tubular abdomens. Both males and females are generally similar in appearance with the front pair of legs longer in length in adult males in both species. The two species can be differentiated by the short, stout spines on their legs. A crocata male spider measures 9-10 mm and females 11-15 mm. Whereas, the erthrina male spider measures 7-8mm and females 9-10mm. There are notable differences between Dysdera crocata and Dysdera erythrina, including size and leg spination.
Most spider species have eight eyes, but the Woodlouse spiders have six, arranged in a semi-circle. They are slow-moving, short sighted and largely nocturnal hunters. Interestingly, they don’t use webs to capture prey. During the day, they are usually fund inside an oval white silk cell attached to surfaces under stones or wood. Within these silk cells, they moult and build their egg sacs.
Both species are found where woodlice are in abundance such as under logs, rocks and leaf litter. Typically, the Dysdera crocata is often found in or near building, including in cellars and kitchens as well as along coastal habitats, gardens and waste grounds. The Dysdera erythrina is more commonly found in permanent grasslands and woodlands. Dysdera crocata is known to occur in regions such as Australia and the eastern United States, highlighting its global distribution.
You may think there is nothing to worry about that this menacing sounding spider will live in another country and our isopod colonies are safe…if you think that, you would be wrong. Both species of the Dysdera woodlouse spider is quite widely distributed in Britain, but absent from much of Scotland and the uplands of Wales.
There are very few spider species that would make a meal on a woodlouse due to most spiders finding them distasteful and often struggle to penetrate through the woodlouse’s armoured plates. Such predator-prey interactions are rare. Woodlice spiders are adapted to exploit thriving on woodlice as a food source. Not only do they find woodlice palatable, but they are also able to hold the woodlice in a vice like grip and pierce through the woodlice exoskeleton to the softer underside. A woodlice defence mechanism of rolling into a tight, armoured ball is no deterrent or true defence to a woodlouse spider.
The length and strength of a woodlouse spider’s fangs puts them among the very few British spider species that can pierce through human skin. If you are ever faced with handling one of these spiders, please do so very carefully. Although their bite is not dangerous it will be briefly painful. Bites can cause localized symptoms due to the spider's venom.
Other invertebrates are not safe from the Dysdera spider, they also prey on silverfish, earwigs, millipedes, burying beetle, centipedes and crickets. The woodlouse spider also preys on other arthropods, and its prey specialization can be compared to spiders that hunt ants.
Not surprisingly, the courtship of these spiders is typically aggressive with the risk of injury to each other being high. Both sexes use their formidable jaws during a complex courtship display. After successfully mating, the female lays a cluster of up to 60 yellow eggs within a strong silk cell. The eggs hatch after 3-4 weeks which are looked after by the female. A month later the female will tear open the egg sac to release the tiny spiderlings. A spiderling will take around 18 months to become an adult and they can live another 2-3 years. Adults of both Woodlouse spider species are present throughout the year but the numbers of Dysdera crocata peak in May and June. Dysdera erythrina adults also show an early summer peak but have a second, larger, one in early autumn.
The woodlouse spider is a highly effective predator, with a remarkable ability to subdue and consume woodlice using specialized tactics for dealing with their armored prey. Its hunting skills and adaptations make it a specialist in this ecological niche. The diet of the woodlouse spider primarily consists of woodlice, but laboratory experiments have shown that spiders fed different prey types, such as flies or isopods, exhibit varying growth and feeding behaviors.
This formidable spider is truly the stuff of nightmares to all isopods!
Isopods are not true bugs, despite common misconceptions. In the pet trade, isopods are often sold in pods for use in terrariums, and some species, such as giant isopods, are also of interest to hobbyists.
The presence of the woodlouse spider can influence the availability of resources and may benefit isopods by reducing competition from other arthropods.
A review of the literature includes information on five other venomous spiders, venomous spiders like the black widow, and the effects of their bites and venom. For identification, guides published by Pearson Education and photographic guides are valuable resources for identifying woodlouse spiders and other arthropods.
Characteristics of Isopod Eating Spiders
Isopod-eating spiders, such as the woodlouse spider, are instantly recognizable by their distinctive features. Their large, curved fangs are perfectly adapted for piercing the tough exoskeletons of isopods like woodlice, allowing them to access the soft tissue inside. These spiders often display a shiny exoskeleton and a tubular abdomen, with coloration ranging from tawny orange to deep red, making them stand out among other spider species. Laboratory experiments have highlighted their aggressive nature, especially when feeding or competing with other spiders. Unlike most spiders, woodlouse spiders possess six eyes arranged in a semi-circle, a trait that aids their nocturnal hunting habits. Their formidable fangs and specialized feeding behavior make them highly effective predators of isopods, showcasing the fascinating diversity found within spider species.
Woodlouse Spider Habitat and Behavior
The woodlouse spider thrives in environments where its preferred prey, woodlice, are plentiful. You’ll typically find these spiders in dark, damp places such as under rocks, logs, and within leaf litter—habitats that provide both shelter and abundant food. Unlike most spiders, the woodlouse spider does not rely on webs to catch its prey. Instead, it uses its large fangs and stealthy movements to ambush and kill woodlice. Females are especially protective, laying up to 60 eggs in a sturdy silk cell and guarding them until they hatch. The spiderlings disperse soon after, beginning their own search for food among small arthropods. In certain circumstances, woodlouse spiders can even adapt to life in terrariums or other controlled environments, where they continue to feed on woodlice and other small arthropods, demonstrating their adaptability and resilience.
Life Cycle and Development
The life cycle of the woodlouse spider is a fascinating journey from egg to adult. It begins when the female constructs a silk cell and lays her eggs inside, providing a safe environment for the developing young. After about three to four weeks, the eggs hatch, and the spiderlings remain under the watchful care of the female until they are ready to venture out on their own. As they grow, the spiderlings undergo several molts, shedding their exoskeletons as they increase in size and maturity. During this time, they feed on small arthropods, including woodlice, gradually developing the hunting skills and physical traits characteristic of adult woodlouse spiders. Laboratory experiments have provided valuable insights into this process, revealing the intricate biology and behavior that underpin the life cycle of these specialized predators.
Prey Acceptance and Preference
Woodlouse spiders are renowned for their strong preference for woodlice as their primary food source. Through both field observations and laboratory experiments, researchers have found that these spiders are typically aggressive hunters, using their large fangs to subdue and feed on woodlice with remarkable efficiency. While they are capable of feeding on other small arthropods such as centipedes, mites, and even other spiders, their evolved preference for woodlice sets them apart from most spiders. This specialization not only ensures a steady food supply but also helps regulate woodlouse populations in their habitats. By focusing on crustaceans like woodlice, woodlouse spiders play a crucial role in maintaining ecological balance, highlighting the complex interactions between predators and prey in the natural world.
