Jewel Spider (Araneus gemmoides)
Photo CD 0023 3291 1601, Image #20 - Credit: Terry Thormin
Jewel Spider - two colour variations
Credit: Terry Thormin
The Jewel Spider is one of about 25 species of orb-weaving spiders found
in Alberta. It is also the species that we get the most calls about,
mostly because it is a very large, impressive spider and it habitually
builds its webs near or on buildings. It is also called the cat spider,
because the shape and pattern on the abdomen reminds some people of a
The first step in identifying this species is to recognize the type of
web it builds. This is true of all web-building spiders; the type of web
narrows the individual down to belonging to a particular family of
spiders. The Jewel Spider builds an orb web, which is the classic type
of spider web that most people think of. It has a well defined hub, lines
going out like the spokes of a wheel, and a spiral going round the hub.
The next clue that one has a Jewel Spider is the fact that it has
probably built its web on or near your home, often over a window to a
room where the light is left on for some time in the evening, or near a
porch light. This does not eliminate all other orb-weaving spiders, but
greatly increases the chances of it being a Jewel Spider. Next, it
should be a very large spider, with two bumps or horns on the abdomen
near where it connects to the head. Finally, if it has a distinct light
line running down the front of the abdomen, and this line is crossed by
a short line that forms a shallow V, that clinches the identification. A
very large Jewel Spider may have an abdomen almost as large as the tip
of one's thumb.
This spider is found throughout southern and central Alberta at least
as far north as Grande Prairie. It is likely found north of that, but
at the present time there are no confirmed records. In North America
it is found from British Columbia to Wisconsin and south to Arizona
TIME OF YEAR
Although the spider is around throughout most of the spring and summer
and often well into the fall, most people do not see it until late July
at the earliest and more often not until August or even September. The
reason is that this is the time when adult females are out and the
spider is thus much larger and visible. In the late summer and fall the
males, which are much smaller than the females, mate with the females
and the female produces a single egg case. The females usually die
within a few days of laying the eggs. The egg case will overwinter, and
on a warm day in spring the eggs hatch and hundreds of babies crawl out.
When conditions are right, the babies send out strands of silk which the
warm rising air carries aloft, often transporting the babies miles or
even hundreds of miles away.
HABITAT AND HABITS
As previously mentioned, this spider has adapted to building its webs on
or near houses. It is therefore most often found in urban centres,
although farm houses will often have a population. These spiders thrive
when the web is built near a light. When the light is turned on at
night, it attracts a large number of insects that become potential food
for the spider. In this situation the spider may have an abundance of
food and may get all it needs in the early part of the night. As a
result the web is often in tatters by morning. The spider will rest
during the day in a retreat, often under the eaves, and only come out to
repair or replace the web in the evening.
Two other large orb weavers with round abdomens are often seen in
Alberta. They are the Shamrock Spider (Araneus trifolium) and the
Marbled Spider (Araneus marmoreus). Both lack the bumps or horns
on the abdomen. Another large orb weaver, the Banded Argiope (Argiope
trifasciata) is fairly common in the prairies. This species has a
more elongate silvery abdomen with black bands across it.
Most calls that come into the museum about this species are from people
who are seeing this spider for the first time. A common comment is
"I've lived in this province for 40 years and have never seen this
spider before. It must be something exotic." It is of course a
native species, although it may be increasing in abundance in
residential areas. Many people are concerned about what would happen if
they are bitten. This is a timid spider that normally doesn't leave its
web and is not at all inclined to bite. If it did bite, a typical
reaction is a bit of swelling and some itchiness that usually lasts only
a few days. I like to tell people that this is the western equivalent to
Charlotte of "Charlotte's Web" fame. It is a great opportunity
to educate your children about spiders and ensure that they do not grow
up being afraid of them.
More and more people are reporting that the outside of their
houses are "infested" with large numbers of Jewel Spiders, and are
asking how to get rid of them. Keep in mind that these spiders feed
on a wide variety of insects, and thus help keep insect populations
under control. These spiders are beneficial!
If you feel that you must get rid of them, try to avoid killing them.
Catch them in a jar and move them to other suitable locations like forest
edges or brushy areas. This is done most easily when they are on the web.
Hold a jar below the spider and the lid above. If done properly, as you
bring the lid closer to the spider, it will drop on a line of silk into
Keep in mind that the population you have this year will be quite
different from the population you will have next year; next year's
population will be the babies of this year's adults, and they will
balloon away the first chance they get. The number of spiders you
support is dependent on what your insect population is like, and
this is largely determined by the number of lights you leave on
after dark. So, to reduce your spider population, turn off your lights!