Royal Alberta Museum: Invertebrate Zoology - Bug Facts

[Caterpillars and Other Immature Insects]

Fact Sheets: Commonly Observed and Asked About Insects and Spiders Found in Alberta

Jewel Spider (Araneus gemmoides)

Jewel Spider
Photo CD 0023 3291 1601, Image #20 - Credit: Terry Thormin

Jewel Spider - two colour variations
Credit: Terry Thormin

INTRODUCTION

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 cat face.

IDENTIFICATION

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.

DISTRIBUTION

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 and Missouri.

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.

SIMILAR SPECIES

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.

COMMENTS

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 the jar.

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!

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Last update: August 19 2004