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Parasites of the Trap Door
Spider Bothriocyrtum californicum
(Araneae, Ctenizidae)Martin G. Ramirez
Department of Biology
Loyola Marymount University
Los Angeles, CA 90045-8220 |
The Spider: Aerial view of a large
B. californicum female.
© 2000 Frank Starkey/SCIC |
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Bothriocyrtum californicum is a large and robust trapdoor spider with
populations in Arizona, California and Baja California, as well as on two of
the California Channel Islands, Santa Catalina Island and Santa Cruz. Once a
spiderling leaves the maternal burrow, it quickly constructs its own nearby and
remains there for the rest of its long life (perhaps 20 years or more), enlarging
the burrow each year. Given its limited dispersal abilities and the extensive
destruction/fragmentation of its hillside habitat on the southern California
mainland, it is likely that when a population of these spiders disappears for
whatever reason at a particular locality, that site will remain empty, given
the challenges faced by potential re-colonizers trying to navigate the human-dominated
landscape surrounding each site.
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The Door: The silk-hinged door at the entrance of a B. californicum
burrow. Note the silk ring visible around the dark center; this is
used to seal the door in place when the occupant does not want
to be disturbed.
© 2000 Frank Starkey/SCIC |
Since B. californicum is an arachnid which is quite possibly threatened
or endangered, the goal of this research is to evaluate the role of its parasites
as potential causes of population extinction. From a management perspective,
knowing more about these parasites and their potential impact on B. californicum would
be quite valuable. The current research was inspired by limited observations
suggesting that in some cases, the parasite load can be so significant as to
lead to the extinction of local B. californicum populations (e.g. Santa
Cruz Island, 1988, unpublished data).
Traditionally, only two parasites were known as having B. californicum as
host, a jet-black spider wasp (Psorthaspis planata) [adult females sting
spiders and lay eggs on them that develop into hungry larvae that eat the spider
from the outside-in] and a small-headed fly (Ocnaea smithi) [their larvae
live internally, eating the spider from the inside-out]. Then, based on considerable
sampling of B. californicum populations in the 1980's/1990's, my students
and I reared a green spider wasp from the Channel Islands (based on Santa Cruz & Santa
Catalina Island sampling in 1988) and a blue spider wasp from a site in San Diego
County. While the blue and green wasps may actually be known to entomologists,
their use of B. californicum as host is new to science and is something
I will publish on as soon as we can.
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The Scientist: Dr. Martin G. Ramirez
in the field, holding a B.
californicum burrow encased
in
a chunk of earth at Little arbor.
copy; 2000 Frank Starkey/SCIC |
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In any case, when one examines B. californicum burrows
for spider wasp cocoons (they are large, obvious structures), one could be now
be looking at the handiwork of three possible wasp "killers": black, blue, green.
Since it is possible to find burrows in the winter with wasp cocoons which still
contain the developing wasps [adults emerge in large numbers starting in April],
we spent many days during spring 2000 sampling B. californicum burrows
on both the mainland and Santa Catalina Island in search of spider wasp cocoons.
A number of these are "fresh" and are being held in lab in anticipation of wasp
emergence. Naturally, we are wondering what such rearings will reveal: will San
Diego samples yield a mix of black and blue wasps, with samples farther north
producing only black ones? And what will Santa Catalina Island samples show:
only green; some green, some black; or some of all three (black, blue, green)?
Down the road, we will be applying PCR techniques to this who-done-it story,
as the cocoons of each wasp (black, blue, green) should be distinguishable genetically,
enabling us to determine parasite loads post-facto, based largely on the examination
of empty cocoons in burrows. Overall, having samples from Santa Catalina Island
has greatly enhanced this pioneering effort in "spider forensics". |
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The Mad Spider: A large B. californicum female
in attack posture, with sharp fangs clearly evident.
© 2000 Frank Starkey/SCIC |
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The Burrow: B. californicum burrows
are completely lined with silk. This
image shows the entire silk lining (note door still attached on right)
which has been removed from a burrow. Note the spider wasp cocoon
(right cut-out) and spider remains (left cut-out) contained therein.
© 2000 Frank Starkey/SCIC |
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The Victim: Body parts (dark black
material near image center) are all that's left of an
unfortunate B. californicum which was consumed by a spider wasp larvae.
© 2000 Frank Starkey/SCIC |
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The Cocoon: A close-up of the spider
wasp cocoon.
© 2000 Frank Starkey/SCIC |
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The Escape Hole: A close-up of
a spider wasp cocoon, showing the hole from which
the newly formed wasp emerged to begin its own adult life. Note the cap-like
"lid" hanging just below the escape hole.
© 2000 Frank Starkey/SCIC |
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