Hobo spider. Property of: Tobias Mercer


Almost everybody knows that spiders are known for having four pairs of legs, but did you know that they have a total of six pairs of appendages?  The hobo spider has fours pairs of “true” and jointed legs, one pair of chelicerae, and one pair of pedipalps.  The chelicerae and pedipalps are actually modified legs.  As you Teeth on the chelicera. "Courtesy of the Utah Plant Pest Diagnostic Lab, Utah State University Extension"may have guessed, the “true” legs are used for walking, but what about the chelicerae and pedipalps?  The chelicerae are used for feeding, but they also contain the fangs and venom.  The pedipalps also are used for feeding, but they are used for reproductive purposes too.  The ends of the pedipalps on the male spiders are swollen at the ends.  All of these adaptations have separated the spiders and other members of the Chelicerata from the other arthropods, and they have also allowed the spider to be more successful in its habitat.

The hobo spider has a skeleton for structure and support, but it is much different than the skeleton of humans.  Humans have a skeleton on the inside of their body so it is called an endoskeleton, but spiders actually have a chitin-baHobo spider. Property of: "Courtesy of the Utah Plant Pest Diagnostic Lab, Utah State University Extension"sed skeleton on the outside of their bodies called an exoskeleton.  The main function of the exoskeleton is protection, support, and a site for muscle attachment.  There are four main regions of the exoskeleton.  They include the epicuticle, procuticle, epidermis, and basement membrane.  The epicuticle prevents the spider from drying out, and the procuticle is made up of chitin fibers and a protein matrix for support.  The epidermis secretes the cuticle layers and the basement membrane is there for support.

The exoskeleton of the hobo spider does not grow with the spider, so this poses a problem when the spider gets bigger.  Spiders and other members of the arthropods solve this problem by a process called molting.  Molting is when the organism loses their old exoskeleton, grow a little larger, and then produce a new exoskeleton that fits their new body size.  This allows the hobo spider to grow in size without having to lose the support and protection of the exoskeleton.   The hobo spider hasHobo spider eyes. "Courtesy of the Utah Plant Pest Diagnostic Lab, Utah State University Extension" 8 eyes that are arranged into two rows of 4.  There are many species of spiders who have compound eyes that allow them to see extremely well.  This is not the case with the hobo spider.  Its vision is not that great and it has a hard time distinguishing things from more than a couple of feet away.  Although, what the hobo spider lacks in vision, it makes up for with its ability to feel around in its environment.

Spiders, as I’m sure you know, are able to spin webs made out of silk.  This is also true for the hobo spider.  Female hobo spiders produce webs and wait in them for their prey.  At the end of their legs, Tegenaria agrestis possess mechanoreceptors.  Using these mechanoreceptors, the spider is able to detect different pressures being generated across the surfaces of the web.  This allows it to sense where and when a prey item lands on the web.  When the prey does land on the web, the hobo spider quickly bites it, injects it with venom, and then consumes it.  Having these mechanoreceptors allows the hobo spider to obtain food while having poor vision.
Setae.  "Courtesy of the Utah Plant Pest Diagnostic Lab, Utah State University Extension"