The Find-a-Spider Guide

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Spider Identification Guide

The majority of spider species are not easily identified by the non-expert. This is partly because individuals of two different species sometimes look very similar to one another or, conversely, two individuals of the same species show enough variability in physical appearance to be perceived as being different species. Visitors to this website who do not have an extensive knowledge of spider classification may even be confused or overwhelmed by the terminology associated with spider recognition. If you are such a person you might like to visit the identification conventions page that has now been added to the Find-a-spider website.

If your ambitions are more modest but you do have a spider you would like to identify, a good way to start might be to seek answers to at least some of the following questions:

1. What does your spider look like?
The physical characteristics of a spider are of great importance when its identity is being established. Each individual spider page included in this guide contains at least one image of the spider as well as some significant facts about it. If some of the terminology used is unfamiliar to you, visit the glossary page for a set of illustrated definitions.

2. What sex is your spider?
Males and females of the same spider species are sometimes very different in size, markings and general appearance. This is known as sexual dimorphism. All mature male spiders have the terminal segments of their palps modified for mating whereas the palps of females are like short legs. Conversely, on the underside of the abdomen of araneomorph females is a species-specific epigynum which the male lacks.

3. Is your spider an adult or is it an immature spiderling?
Most spiders pass through about five immature stages called instars before reaching adulthood although in rare instances maturity may be reached in fewer steps. These young instars (with the possible exception of the penultimate one) will normally be smaller than an adult of the same species. They can also be expected to have immature or non-existent mating apparatus and differences in marking patterns. Sometimes the sex of a living spider cannot be determined until it becomes an adult. For these reasons you may find some spider specimens impossible to identify with certainty.

Most species have a particular mating season, usually spring, summer or autumn, and for many species no mature males can be found except during this season. Egg sacs will often be found near the end of the mating season and immature spiders will generally be most common shortly after mating or in spring.

4. Did you find a web or egg sac as well as the spider?
The shape and general appearance of any web or burrow a particular spider has produced can often be used to verify its identity. Some species create net-like webs for trapping flying insects and the shapes and detailed construction of these are reproduced very faithfully by each species. Unfortunately, many webs are quite fragile and damage inflicted by a struggling insect or by a large animal could change the appearance of a spider's web to the point where it is no longer useful for classification purposes.

Spiders that burrow or build leafy retreats also tend to be remarkably consistent in the architecture of the home they have constructed for themselves. It is for this reason that some images of burrows, retreats and egg sacs are presented in this web site. It is usual for female spiders to enclose their eggs in an egg sac until the spiderlings hatch out, and once again the shape of this varies greatly from species to species. In some cases a semi-rigid sphere is produced but many spiders prefer to make a fluffy mass of silk or a flattened pillow. Occasionally, the shape and colour of the egg sac seem to involve deliberate camouflage.

5. Where did you find your spider?
Most spider species have habitats and geographic locations in which they are most common and this can sometimes be very useful for verifying the identity of a particular spider. On the other hand, individual spiders will occasionally be found in unexpected places, perhaps because of human intervention, so no identification should be made purely on the basis of the place where the spider was found.

You may now feel ready to commence comparing your spider with photos of named species but it might still be a good idea to first check out the Before you begin... page.



Email Ron Atkinson for more information.    Last updated 21 April 2015.