Sexing Spiders and Determining Maturity

All spiders, like other arthropods must grow by molting. If a spider you collect is not mature, you can house it in an appropriate cage in the classroom, and you will probably be able to see it molt. The molting process is amazing. The animal literally makes a new exoskeleton and then climbs out of its old skeleton. It is probably similar to simultaneously pulling 8 legs out of the equivalent of very tight blue jeans! For all spiders except tarantulas, once the animal is sexually mature, it will not molt again.

The Male Wolf Spider
Unless you wanted to look at chromosomes, you can only determine the sex of a spider after it is mature. It is easiest to recognize mature males. A male that is sexually mature will have swollen pedipalps (also called palps) that have a complex, sclerotized structure on the ventral side of the palp. This structure holds the sperm and is the spider's means to transfer sperm to the female.

This figure shows the ventral view of a male. In many cases you can recognize a male that is one molt away from maturity by the presence of swollen palps but has no scerotized structure on the palp. You can generally see if the palps are swollen by looking at the spider with a hand lens or even without magnification.

The palps serve many functions in spiders and particularly in wolf spiders: not only is the palp the structure that transfers sperm during mating, but in wolf spiders the base of the palp has a stridulatory organ that is used to make sounds during courtship, and it has many chemosensory hairs that are helpful for the male to recognize the pheromone of the female.

The Female Wolf Spider
Mature females can be recognized by the presence of the epigynum on the ventral surface of her abdomen. The epigynum is the external part of the structure that holds the sperm and is the location from which eggs are deposited.

It is harder to see the epigynum on the female than the pedipalps on the male. Usually, you need to look at the ventral side with magnification (either a handlens or a microscope). With practice it is possible to immobilize a female with cotton against the side of a vial in such a way that you can look at the epigynum with a microscope.

Female carrying egg sac attached to her spinnerets.

One way to recognize female wolf spiders is to find them carrying their eggs in an egg sacs attached to their spinnerets. When the eggs hatch, they will carry their babies on their abdomen. Female wolf spiders are the only spiders to show this form of parental care

If you find a wolf spider that is carrying an egg sac, it is most certainly a female. Henri Fabri, a french naturalist and writer from the late 1800's noted that a female wolf spider will be willing to carry any object the approximate size and shape of the egg sac. He found he could get the female to carry small stones and shells. James Wagner studied how the females are inhibited from biting the babies.

When the egg sac hatches, the babies have already undergone a molt in the egg sac. They climb out and will spend the next week or two riding on the abdomen of the female. In some cases, the female will carry several hundred babies! This provides some protection for the babies and may also provide a means for the babies to be dispersed. Jerry Rovner and Gail Hitashi studied the structure of the abdominal hairs on which the spiderlings hang.

The ventral view of female.
The epigynum is near where the
cephalothorax joins the abdomen
and is shown enlarged on the right.

Courtship and Copulatory Behavior
Courtship behavior is often described as those behaviors that normally lead to copulation. In spiders, as well as other arthropods, these behaviors are highly ritualized and often species specific. For those groups that have well-developed eyes (jumping spiders and wolf spiders), the courtship often includes visual signals such as movement and bright contrasting colors.

Many of the web-building spiders rely on pheromones (usually from the female) and web vibrations (from the male). In many wolf spiders, the female produces a pheromone that is associated with the draglines that elicits courtship behavior in the males. In wolf spiders, the courtship behavior often includes visual elements as well as acoustic or vibratory elements. Courtship behavior is usually species specific, and in some cases, the behavior may be the main difference between closely related species.

Wolf spiders provide a variety of opportunities to observe behavior. If you have two mature individuals, you can look for either courtship behavior or agonistic behavior by placing two individuals together. It is always a good idea to feed both spiders before putting them together to observe courtship.

Copulatory behavior is the behavior involved in transferring sperm from the male to the female. Spiders are nearly unique in the animal kingdom in that the sperm is transferred by the palps, but the sperm is produced in the abdomen far separated from the palps. When mature, the male will build a "sperm web," a small web in which he will deposit the sperm from his abdomen. He will then take up the sperm in the complex structure of his palps where the sperm is stored until he finds and courts a female.

Species Determination
All spiders are members of the Phylum Arthropoda, Subphylum Chelicerata, Class Arachnida. They comprise the Order Araneae. Within the Araneae, there are three suborders, the Mesothele (known only from Indonesia and from fossils), the Mygalomorphae ("tarantuloid" spiders) and the Araneomorphae (the so called "true spiders"). The family Lycosidae is one of the largest spider families with some 2200 species world wide (Coddington and Levi 1992). In the US there are a large number of species of wolf spiders including some that are very small (a few mm long) to the Hogna carolinensis that are 3 cm long (not counting legs).

Taxonomy of wolf spiders:

Phylum: Arthropoda
   Subphylum: Chelicerata
      Class: Arachnida
	Order: Araneae
	   Suborder: Araneomorphae
	      Family: Lycosidae

In order to accurately identify spiders to genus and species, you need a mature specimen because the palps and epigyna are the structures that are necessary for identification. This underscores the importance of being able to recognize mature male and female spiders. Vincent Roth’s Guide to Spider Genera is one the most useful places to start in terms of identification to genera. Once the genus is identified, you must go to either a taxonomic revision of that genus or to the original descriptions in order to identify spiders to species.

Confirmation of species identification is accomplished by comparing your specimen with a specimen identified by a specialist or by sending one or more specimens to a taxonomic specialist. That person will identify the specimen and send it back to you, and you can then compare other specimens to it. It is through this process that you build a voucher collection or a “library” of identified specimens. It can be very satisfying to know the genus and species of the animals you are working with. To be valuable, a voucher collection must be curated properly and must have accurate and complete labeling of each specimen. Scienctific work requires the accurate identification of specimens.

Preserving Specimens
As spiders are somewhat soft bodied, they are stored in 75% ethanol rather than being pinned like insects. Each specimen must have a locality label and an identification label. Spiders can be frozen (to kill them quickly) and then placed in 75% EtOH.

The locality label identifies where the spider was found, the date, the conditions and who collected it. All of this must be typed or written small enough for the label to fit in the vial with the specimens. It is also essential to keep a separate record of the collections in a field notebook. The writing must be in ink that will not dissolve in EtOH!

Vial with labels and preserved spider

Here is an example of the information required:

Miss. Marshall Co. 3 mi S. of Waterford
R3W T5S Sct. 35 34 degrees 36'N, 89 degrees 28'W
13 March 1996, night collection
G. Stratton
deciduous leaf litter, small woods in town

If it is available, include longitude and latitude of the exact location the spider is found.

The identification label would look like this:
Family Lycosidae
Schizocosa ocreata (Hentz)
2 M & 3 F
det. G. Stratton 1996

Note: the name "Hentz" written after the spider's name is the name of the person who formally described that species. When it is written in parentheses it shows that that species was originally described under a different genus. M = male, F= female. "Det." means "determined by". Genus and species names are italicized or underlined; only the genus name is capitalized.

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