Synonyms and other taxonomic changes
all North American spiders belong to suborder Opisthothelae
~43,500 spp. in ~4,200 genera of ~110 families worldwide(1)
A guide to easily identifiable spiders:(2)
; a good inexpensive guide to common spiders and other arachnids:(3)
Two body parts: cephalothorax
Eight legs attached to cephalothorax
visible silk glands
Look at the front of your specimen, where the "face" of the spider is. You will find two small appendages that resemble little legs. These appendages are called pedipalps
, and are used for sensing the spider's immediate environment, for assisting with eating, and for males, reproduction (specifically sperm deposition). Please refer to the Anatomy section above for a picture of a spider with the pedipalps labeled.
If the pedipalps resemble boxing gloves (the tips of the pedipalps are swollen), it is an adult male. Here is an example of an adult male (Agelenopsis grass spider):
If the pedipalps are not swollen, it is either a female, or an immature of either sex. (Characteristics of the female genital opening, the epigynum
, may be used for species-level identification.) At this point, more information is needed about the spider (shape, size, location, coloration, style of web, etc.); this information can be used to determine the maturity level of the spider, which would indicate whether it is an adult female or an immature spider of either sex.
Adding habitat to your information may help with ID. For example, Zygiella x-notata and Zygiella atrica occur in urbanized habitats, the former on buildings and the latter on trees. The similar-looking Parazygiella dispar is found in natural forest.
Images critical for identification
1. Eye arrangement will help you place a spider to family.
2. Body pattern can help place a spider to genus (and sometimes species).
3. Epigynum close-ups for adult female spiders:
(having a plastic bag on hand is useful for this)
4. Palp close-ups for adult male spiders:
(especially side views)
Spiders eat whatever insects are available in their environment. Web-making spiders catch their prey with a web, whereas hunting spiders ambush their prey without the use of a web. Every species of spider is uniquely evolved to fit its environment. Spiders in hot, dry climates can last longer without water than a spider from a super humid climate. Also, spiders that are synanthropic (associated with human habitation) have evolved to survive indoors where typically little or no water is available and food is less plentiful.
There are a few different ways or terms to describe a spider's life cycle. One could delve into such terms as prelarva and postembryonic if one wanted, but here is the gist of it:
Egg--> Spiderling--> Immature/juvenile/subadult--> Penultimate--> Adult
Spiders must shed their exoskeleton, or molt, in order to grow.
They will molt as many times as is needed (approx 4-12) to reach adulthood. The penultimate stage can most simply be described as 'next to last'. A penultimate spider has signs of underdeveloped genitalia and needs only one last molt to become adult. After that last molt, the genitalia is fully revealed and entirely developed. True spiders, or araneomorphs
, will not molt past adulthood. Their next step is, eventually and inevitably, death. That is in contrast to the mygalomorph
spiders who live much, much longer and continue to molt once or twice a year through their long adult lives.
While it's true that most have venom (the single exception in our area: Cribellate Orb Weavers in the Family Uloboridae
) the bites of all but a few are only mildly painful, and have no lasting effects.
Believe it or not, almost all species are not harmful to people, but are actually beneficial because they catch and eat a lot of insects that can be pests. Spiders do not seek out, chase, or randomly attack people, nor do they carry grudges against people. If you leave them alone, they will leave you alone.
Most people are bitten because they were playing with the spider (which is effectively "asking" to be bitten), or the spider felt threatened without a chance to escape; many times, surprising the spider was completely accidental. Depending on your geographical location, there are only a few spiders that you need to be familiar/concerned with (see the comments below on the spiders of potential medical concern).
If you aren't sure whether the spider you have might be harmful, leave it alone and do not kill it. If you have to move it, please refer to the "Relocating The Spider" comments below.
Spiders of Potential Medical Concern:
Spiders with persistent rumors of medically significant bites that are not supported by scientific literature:
Yellow Sac Spider aka Longlegged Sac Spider (Cheiracanthium spp.)
: this is probably not true and is based on lab experiments on rodents, not HUMANS! Please read this paper
that shows their venom is not necrotic to human cells.
Hobo Spider (Eratigena agrestis, formerly Tegenaria agrestis)
: this, also, was based on lab experiments on rodents, not HUMANS. A Hobo spider has never been verified as the culprit in any spider bites on humans, despite the rumors and misinformation. In the most recent literature, this spider is AGAIN shown to NOT BE MEDICALLY SIGNIFICANT. Please read this paper
Moving most spiders to a new location (outside the house?) is not difficult. You will need:
a clear glass or cup; it should be clear so you can see where the spider is.
a card, or stiff piece of paper
(1) Carefully place the cup over the spider (careful not to pin the legs under the rim of the cup).
(2) Gently and slowly slide the paper under the glass; as you push the paper under the glass, let the spider walk up onto the paper.
(3) Once the paper is completely underneath the cup, gently pick up the paper and glass, making sure not to create gaps between the paper and glass (the spider might escape, which means you have to start all over again... :) ).
(4) Turn the glass over while keeping the glass covered with the paper.
(5) Take the spider to the new location, while holding the paper over the glass. This is a good time to look at your spider, examine its markings, and learn about it.
(6) Place the glass on its side on the ground and remove the paper.
The spider will walk out of the glass in a few moments. If it seems reluctant to exit the glass, gently tilt the opening the glass toward the ground, and gently shake. The spider will eventually wander out. :)
Alternative technique (from Rod Crawford): "...something that works much better is putting a container with a lid in front of the spider (or under, if the spider is hanging in midair) and touching the spider from behind with the lid. Spiders have a reflex to run forward when touched from behind."
Larvae in the subfamily Mantispina prey on spider eggs. See more info here
"Many hunting spiders possess dense hair tufts called scopulae under the claws of their tarsi (feet). These scopulae allow many spiders to walk on smooth vertical surfaces, across ceilings and even window panes. Each individual scopula hair splits into thousands of tiny extensions known as end feet. These end feet increase the number of contact points of the tarsi with the surface, creating great adhesion. This is similar to the adhesion forces at work in vertebrates such as skinks and geckos, which can also walk on ceilings with ease. The scopulae can be erected or laid flat by hydraulic pressure through changes in the pressure of the hemolymph (blood supply)." (Australian Museum 2014
Information on rearing and studying spiders in(4)
Canadian fauna overview(5)
Higher classification and global taxon numbers(1)