Is it really a spider?
Some insects are frequently mistaken for spiders, and vice versa. Both are arthropods but belong to two separate classes within Arthropoda: Insecta and Arachnida. The following is a fairly simple explanation about how to tell these two types of animals apart. Before trying to identify your “spider,” you’ll want to confirm that it is indeed a spider.
All spiders have two body segments and eight legs. If your creature doesn’t have two body segments and eight legs, you don’t have a spider. Spiders also have two short appendages, one on each side of their face, that are called “pedipalps” or simply “palps.” They are basically modified legs that aid them in food manipulation, mating, and sensing their environment. They do not count as legs, but you will probably notice them while counting the real legs, so it is worth mentioning. Spiders will occasionally lose legs in battle, during mating, or during molting, so if your supposed spider has less than eight legs, keep that in mind.
Insects have three body segments, six legs, and two antennae. Some types of insect have long antennae which can be mistaken for a 4th pair of legs, so look closely to be sure of what you’ve got. One of the most common insects mistaken for a spider are true bug nymphs, such as those of the Assassin Bug, because they are very “leggy” and their antennae are long. Also, members of the arachnid order Opiliones (the Harvestmen) are often thought to be spiders but, if you look closely, you’ll see that they have only one body segment, meaning they are not spiders. They are related to spiders, though, and are indeed arachnids, but not of the same order as spiders.
|Three pairs of legs (six legs total)||Four pairs of legs (eight legs total)|
|Three body sections (head, thorax, abdomen)||Two body sections (cephalothorax, abdomen)|
|Antennae present||No antennae (but has short pedipalps near mouth)|
|No spinnerets (but some insects have paired tail-like appendages called “cerci”)||Spinnerets present on tip of abdomen|
|Wings often present||No wings present|
When a spider is first described to science, it’s given a Latin or Greek name. This is THE name. This is the “scientific name.” These names are chosen by the taxonomist who first describes it (or, in some cases, by the spider’s discoverer), but must adhere to rules set forth by the International Commission on Zoological Nomenclature. For example, the genus name Eriophora means “wool-bearing” in Greek; those spiders are covered in wooly hairs, which prompted Eugène Simon to select that naming in 1864. On the other end of the spectrum are names that have nothing to do with the physical attributes of the spider. The genus name Platnickina, for instance, was selected by Ahmet Koçak & Muhabbet Kemal in 2008 to recognize Norman Platnick for his contributions to arachnology. Some names are the same as Greek gods, like Eris, the goddess of chaos and discord: in 1846, Carl Ludwig Koch named a genus of jumping spider after her.
The genus and species of a spider form a unique title that can’t be applied to any other spider. It is practically a barcode. Researchers do not normally assign a “common name” or nickname to the spider. It is only for the general public that common names are issued for abundant or economically important species. These common names are easier for the average person to learn and pronounce. It’s much easier to say “Common House Spider” than it is to say “Parasteatoda tepidariorum.”
The Committee on Common Names of Arachnids, in their 2003 edition, listed 115 common names for specific species in North America. This is barely 3% of the 4,000 or so species that are currently known from that area. Hence, though common names may be “common,” they are not commonly given or even needed.
Besides specific species that have their own common name (e.g. “Goldenrod Crab Spider” for Misumena vatia), some entire families have been given an all-encompassing one. For example, the entire family Lycosidae, which contains roughly 250 species in North America, has been given the common name “Wolf Spiders.” This is why a scientific name is incredibly important if you wish to find more exact information on the spider you have. For example, search for Hogna carolinensis, instead of “Wolf Spider,” and you will find the information and images that are of the same species as your spider. A scientific name is somewhat of a direct hit, whereas a name as common as “Wolf Spider” is very broad.
One of the best things about scientific names is that they translate across all languages, all geographic locations, and all individual personalities (some published field guides make up common names that have never even been heard of by anyone but the author, by the way).
Spiders, like most living creatures, are assigned to ranks in what is called a taxonomic hierarchy. Creatures with similar physical characteristics and/or genetic traits are placed alongside one another in each rank. Here is how a thin-legged wolf spider is placed, for example (and yes, spiders are animals):
Kingdom: Animalia (all animals)
Phylum: Arthropoda (insects, arachnids, crustaceans, other “joint-legged animals”)
Class: Arachnida (spiders, scorpions, ticks, mites, harvestmen, etc)
Order: Araneae (all spiders)
Family: Lycosidae (wolf spiders)
Genus: Pardosa (thin-legged wolf spiders)
Species: Pardosa atlantica (no common English name)
Note that the genus and species names are italicized. The combination makes for the scientific name of the animal.
For amateurs or the casual observer, it isn’t always necessary to find the exact genus and species of a spider. Sometimes knowing which family is enough. Most members of a family share common behaviors and life histories, so knowing which one your spider belongs to can help you to become familiar with your spider and know what to expect from it.
Worldwide, 112 spider families are recognized so far. North America currently has representatives of 71 of those (as of 2013). Taxonomy is a fairly fluid thing; as more information is gained about spiders, new families are created or split apart or transferred to other families, so these numbers are always subject to change. Sometimes taxonomy is debatable, with different researchers taking different positions as to what belongs where. More often than not, however, there is agreement at the family level.
Identifying Spider Family
How do you find out which family your spider belongs to? Family level identification comes with experience and the guidance of scientific publications, but there are a few tricks that can help those unfamiliar with spiders.
Of much importance are the eyes of the spider. How many does it have? How are they arranged? How does each eye’s size compare to those around it? Most folks who are afraid of spiders don’t want to get close enough to look at a spider’s eyes, so consider getting a spouse, other family member, or a friend to do so.
Here are some drawings of the eye arrangements of a few spider families (some are specific to a certain genus, which is noted in the caption when applicable). They should help you with the commonly encountered spiders in and around your home in North America. Note that not every spider family is represented here, especially the ones whose eye arrangement can be easily confused with a different family when using diagrams like this. Actually, even some of the ones pictured here can still be confused for other families; double-check what you come up with and see that the other characteristics of the spider also match with whatever family you settle on. Also note that within a single family, there can be variations in the arrangement for separate genera or species. These diagrams show a view of the spider from the front. Be aware that sometimes all the eyes are not visible from a single perspective. You’ll have to look closely at the spider. You can buy a pocket loupe (a little magnifying glass) for fairly cheap or there are, of course, other methods of magnification. Sometimes taking a macro photo with your camera and then zooming in on the eye area works great. All spider eyes are oval or fully circular. The crescent shapes in these drawings are only a matter of perspective having to do with the angle the eyes sit or their distance away from the front of the face. (Please forgive the freehand mouse drawings):
- Family Lycosidae – the Wolf Spiders
- Family Salticidae – the Jumping Spiders
- Family Salticidae, genus Lyssomanes – the Magnolia Green Jumpers
- Family Araneidae – the Orbweavers
- Family Pisauridae, genus Dolomedes – the Fishing Spiders
- Family Pisauridae, genus Pisaurina – the Nursery Web Spiders
- Family Ctenidae – the Wandering Spiders
- Family Oxyopidae – the Lynx Spiders
- Family Philodromidae – the Running Crab Spiders
- Family Dysderidae – the Woodlouse Hunters
- Family Tetragnathidae, genus Tetragnatha – the Longjawed Orbweavers
- Family Thomisidae, genus Xysticus – the Ground Crab Spiders
- Family Agelenidae, genus Tegenaria – the Funnel Weavers
- Family Agelenidae, genus Agelenopsis – the Grass Spiders (aka Funnel Weavers)
- Family Selenopidae, genus Selenops – the Flatties (aka Crab Spiders)
- Family Sparassidae, genus Heteropoda – the Huntsman (aka Giant Crab Spiders)
- Family Sparassidae, genus Olios – Giant Crab Spiders (aka Huntsman)
- Family Sicariidae, genus Loxosceles – the Brown Spiders (includes the Brown Recluse)
- Family Uloboridae, genus Hyptiotes – the Triangle Weavers
- Family Zoropsidae, species Zoropsis spinimana – the False Wolf Spider
- Family Deinopidae, species Deinopis spinosa – the Net-casting Spider (aka Ogre-faced Spider); note that the four other eyes are not visible from the front.
- Family Diguetidae, genus Diguetia – the Desertshrub Spiders
- Family Antrodiaetidae, genus Antrodiaetus – the Folding-door Spiders (aka Turret Spiders); these are primitive spiders (mygalomorphs).
- Family Segestriidae – the Tube Web Spiders
- Family Scytotidae – the Spitting Spiders
Another important thing is where the spider was found. Was it in a web? If so, what kind of web? These are things one should pay attention to. Most of spider identification entails being very observant and paying close attention to details. Because spiders can often be found outside of their normal habitat (e.g. a web-based spider can be found walking on the ground without a web to be found), sometimes you have to focus on other details: namely the eyes, if you’re new to spider identification.
Spider Species Identification
Spider identification to species level is not easy, even for a trained professional. Accurate identification of a spider is done by viewing the tiny structures of their anatomy under a microscope. Most important for species level identifications is the examination of the spider’s reproductive organs. This can only be done when those organs are completely developed, which means the spider must be a fully matured adult. What one sees under a microscope must then be matched to a key in published papers written by researchers. This is the ONLY ACCURATE WAY TO IDENTIFY A SPIDER TO SPECIES. Identifications done by matching colors and patterns of a spider can only be guesses; granted, some can be pretty accurate, especially when done by an expert but, without checking the genitalia of a spider, those identifications are technically never 100% sure. This is species level that we’re talking about, by the way. Placement to family (and sometimes genus) is much easier and can usually be done without inspection of the genitalia.
Currently, over 44,000 species have been described worldwide. Roughly 4,000 of them exist in North America. That number is always increasing; new species are discovered all the time and hundreds, if not thousands, are waiting in line to be formally described by professionals. It is estimated that we may not even know of half the species in existence yet! The sheer amount and variety of spiders out there is one thing that makes species level identification difficult.
When a new species of spider is first discovered, researchers professionally describe it and draw diagrams of the tiny details that make that spider unique. These diagrams are incredibly detailed and meticulously drawn to exactly match the spiders’ parts; they are not “rough sketches.” The most important areas that are drawn are the fully-developed reproductive organs, which means the epigynum of the female spider and the pedipalp of the male (see images below for location of those organs on the spider’s body). Those organs of the spider are unique to each species. They are a sort of lock and key system, one that is as unique as our fingerprints are. For many species, an examination of both the outer and the inner structures of the female’s epigynum is necessary, which means an actual dissection must take place at some point. Even more difficult, some species are haplogyne, meaning they have no outer epigynum, and they have to be dissected to begin with. Colors and patterns of many spiders can be extremely variable, whereas genital structures typically remain a constant across most specimens of the same species. We say “most” there because, even still, there are some species that exhibit variation even in their genitalia, and that’s something you come across as you grow more experienced with identification… it’s yet another thing making species level spider identification difficult. In recent times, we have the help of DNA sequencing, but even that can be problematic.
Scientific papers and related literature are the spider identifier’s best friend. You need books, you need papers, you need all that you can get! You cannot identify a known spider without standing on the shoulders of those that came before you and recorded information. The drawings previously mentioned are published in papers in scientific journals and books. One of the trickiest parts of spider identification is first figuring out which papers have the information you require and then finding out where, or how, you can obtain said papers. Thankfully, nowadays we have the assistance of the most wonderful and powerful resource! World renowned arachnologist, Norman Platnick, created a website called The World Spider Catalog. The website is hosted by the American Museum of Natural History and it lists every officially described species of spider and all the citation for the published literature that contains taxonomic information on each one. (Even changes in taxonomy are recorded there!) Keep in mind that the list contains only papers that have been published. Unpublished literature will have to be found using other means. Also, the Catalog is only updated to reflect new changes every six months, around June and January of each year, so it’s possible that the newest changes may not always be immediately seen there.
Learning how to use the Catalog to your advantage is actually quite easy. Under each species entry, you will see below it a list of publications that contain information on it. The more recent the paper, the more likely it is to be helpful… but some out-dated papers may be the only ones available, so they’ll have to do. A random example of the citation you will see under a species would be: Levi, 2002: 557, f. 287-290. This is the author’s last name followed by the publication year and the pages and figures that correspond to the species in question. Now go to the bibliography section (via the link at the top of the page) and click the link that contains the publication year (in this case, 2000-2004). Scroll to the 2002 section and find Levi in the alphabetical list. You will see: Levi, H. W. Keys to the genera of araneid orbweavers (Araneae, Araneidae) of the Americas. J. Arachnol. 30: 527-562. Now you have the citation for the paper you need to find. Track down the publisher and find the article (J. Arachnol. means the Journal of Arachnology; eventually you’ll get used to the abbreviations you come across and know what they all mean). Sometimes this requires purchasing of the paper from the publisher unless you have free institutional access offered by your university, lab, or local library (or you have a personal subscription). Fortunately, papers published by the Journal of Arachnology are typically free to download (here’s the one we used in the example), as are those from the American Museum of Natural History, Harvard’s Museum of Comparative Zoology, Psyche, etc. Many others can be found online for free download, you just have to search for them. Sometimes you will find one website trying to sell the paper and another giving it away for free… so always do a lot of searching before you pay for a paper. Try out online archives such as the Biodiversity Heritage Library, Internet Archive, and BioOne, which house countless documents available for free viewing and even download (use scientific names for your searches or you won’t find much). As a last resort, after checking the publisher’s website, online archives, and any other places you can think of, try searching for the paper’s title in Google Scholar. Sometimes this will reveal websites where the paper is being hosted for free, which may even be the webpage of the paper’s author or their affiliated university.
An important note that needs to be thrown in here is that many taxonomic keys are old and out-dated. The study of spiders is quite honestly still in its infancy, even though we have really come so far from where we used to be. There is still much work to be done, more to be learned, and many, many groups to be revised. This is perhaps one of the main reasons spider identification can be difficult. If there’s no current data on something, you’re just stuck… and will have to wait until the group is revised and new literature published which, well, might be a really long time in many cases.
Keep in mind that for species level spider identification, you really must have a stereo microscope. Even if you track down and acquire the papers you need, you will have no way to check your spider’s reproductive organs and other characters against the keys and diagrams in the paper without one. You will realize that at this level of spider interest and study, your list of necessary “tools” will grow. You’ll need to be preserving your spiders in 70-80% ethanol (1st choice if you have access to it in a lab or can buy it at the liquor store) or 70% isopropyl rubbing alcohol purchased cheaply at the drug store (this makes specimens brittle and is not very healthy for humans to inhale, so this is 2nd choice). Spiders are not like insects which can be dried and pinned. They have to be preserved in alcohol. You’ll need forceps (tweezers) for handling them, maybe a petri dish or glass excavated block for sliding them under the microscope, tiny glass beads to help hold the spider in place for viewing, extra vials for storage, eventually a micro dissection kit, extra light sources for your microscope, etc… the list can go on and on. You’ll learn from trial and error (and experience) what you need. It never hurts to ask those around you for help. There aren’t that many spider enthusiasts in this world, so we have to stick together!
With experience, you’ll also learn that species level identifications done on adult male spiders are typically much easier than on adult females. Female epigyne areas, as mentioned earlier, will typically require dissection and sometimes a process called “clearing” in order to accurately identify them. The male pedipalp, on the other hand, is fairly straight forward; normally no dissection is necessary at all (besides the simple act of removing the left pedipalp from the main body of the spider). Also, the epigyne area on a female can often be covered in so much hair that the structures you need to see are completely obscured. You could spend an hour trying to remove the hairs, only to see that you still have to dissect the epigynum anyways! In specimens that have already been submerged in alcohol for a length of time, the hairs can usually be gently scraped off, which is much easier than trying with scissors or a scalpel. The structures of the male pedipalps, in contrast, are never obscured by any hair. You do need to view the palp from as many directions as possible, though. Some structures are not seen in a purely ventral view; you also need to check the lateral views (turning it on its side), as well as any other view that the literature you’re using requires. Sometimes you need to view it from the perspective of the palp’s tip in a way similar to checking a pool cue for straightness. Under a microscope, use indirect light so that it will create shadows that best bring out the shape of the structures.