Wednesday, April 6, 2011

Who Says a Hoarder Doesn't Like to to Share?

Bushy-tailed Wood Rat - Neotoma cinerea (packrat)[2]

Introduction: Pseudoscorpions is a flattened, oval, brown, black or brownish-green colored arthropod with a short fang-like appendage in front of its mouth (chelicerae). The appendage has a fixed and movable finger that allows the “scorpion” to grasp items. Also, like most arachnids it has a pedipalp, which is a pincer-like claw capable of clasping and crushing prey and secreting poison from a gland (1). Unlike the common scorpion it does not possess a long tail and is unable to sting other organisms. It is a small organism that usually reaches 5 millimeters, even though one species is capable of reaching 12 millimeters (3). Pseudoscorpions have spinnerets that allow them to produce silk for the construction of nests. On average females produce three to four clutches of eggs at a given time. The female carries her eggs until the young hatch. Although the lifespan of the Pseudoscorpions is unknown, it is believed that the adult can live anywhere from six months to two years.


Description: Pseudoscorpions feed on small insects and other arthropods, such as ants and caterpillars. They are commonly found in leaf litter, rotten logs, bark, bogs, swamps, homes, and under rocks (1). Packrats, also known as the trade rat or wood rat, are common in the deserts and highlands of western U.S. and northern Mexico, and eastern U.S. and Western Canada. They are characterized by their small stature and bushy tails, piercing call, and surprisingly an attraction to shiny things. As protection from predators, they build complex nests out of twigs and incorporate cactus spines into its design (4). To bind the objects together they urinate on the nest- the sugars and other substances crystallize to fortify the materials (4). Packrats are known for their constant search for twigs, rocks, animal dung, leaves, and sticks to add to their ever-expanding nest. Hence, the term “pack-rat” used to describe a person who accumulates materials.

How do these two organisms relate? Pseudoscorpions have established mutual relationships with birds and rodents (in this case packrats) by consuming other arthropods that invade the nest. Some species are phroretic- live on beetles and large insects, where they feed on mites in return for increased motility.

[5] Cost/ Benefit Analysis: In a phoretic relationship, the transporter gains nothing, while the other organism gains motility. According to The Art of Being a Parasite the Pseudoscorpions can become a burden on the transporter if too many passengers were to climb on board the beetle (6). However, it was observed that the Pseudoscorpion lives in the nest of the rodent. The Pseudoscorpions eats packrat ectoparasites (i.e. larval and adult fleas) and finds a place of shelter from predators, namely for reproduction. The packrat in turn receives relief from fleas, which are a nuisance because they can cause changes in the behavior of the rat, weight loss, and fur loss. All of which reduce the health of the rat, making it more vulnerable to pathogens. There is no cost incurred from this association.

Works Cited






6. The Art Of Being a Parasite



  1. How do the pseudoscorpion get into contact with the packrats? DO they have a certain area or time in which the pseudoscropion is able to attach itself to the packrats? Is there any other insects in which can copy the appearance of the pseudoscorpion and cause distress to the packrats?

  2. You said that the rats urinate on their nests to crystallize to fortify the building materials materials, but do the rats ever reach a point where their nest is so crystallized from their several layers of building, that insects can no longer get in therefore making the pseudoscorpion useless?

  3. Unfortunately, I could not find a lot of information about how the pseudoscorpion encounters the packrat. However, I did find an article entitled Symbiotic Relationships between Pseudoscorpions and Packrats, published by the Journal of Arachnology that explains how the pseudoscorpion encounters the packrat from an evolutionary standpoint. The packrat brings food as well as materials for the construction of its nest into its habitat. As stated above, the packrat uses a wide range of resources to build its nest, including twigs, leaves, and rocks. The pseudoscorpion which typically lives on these same materials is accidently brought into the nest. Over time, the pseudoscorpion adapted to remain in the nest, where there was a stable supply of food.

  4. A packrat’s midden, in other words den, is protected by the urine in a few ways. The sugars and other substances in the urine crystallize cementing the various materials together, in addition to slowing down the decay of materials used to build the nest and to offer protection from predators. I’d imagine that the denser nest would prevent ectoparasites and the pseudoscorpion from entering the nest, because the urine acts as cement creating a thick wall of insulation. Even if the pseudoscorpion was to get into the nest via phoresy, the lack of ectorparasites would decrease the food supply available for the scorpions. That’s what I imagine happening, I could not find actual evidence.