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 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
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.
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.
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.
Female carrying egg sac attached to her spinnerets.
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.
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.
Taxonomy of wolf spiders:
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 RothÕs 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 ÒlibraryÓ 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.
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.
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.
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).
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Araneae
Suborder: Araneomorphae
Family: Lycosidae
Genus:
Species
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.
Labeling
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 If it is available, include longitude and latitude of the exact location the spider is found.
The identification label would look like this: 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. |