Week 4: Collecting Spider Specimens
by Dr. Vladimir Ovtsharenko
Techniques for Collecting Spiders in the Field
Observation and field sketching are useful tools for studying spiders in their natural setting. To identify spiders, you need to get up close with particular individuals, not just rely on drawings and photographs done in the field. This is why collection is a must.
A variety of collection methods is available, and each one is suited to collecting in a certain type of environment. Often, the type of vegetation determines the kinds of spiders you will find, and you would use one technique to collect spiders that live on plants and another for spiders that live on the ground.
Below are explanations of six collection methods, including information on the sort of terrain and specimens they are best suited to. Since these techniques will collect not only spiders but other arthropods as well, you will need to sort through the organisms to find your spider specimens.
|Vlad demonstrates the use of a sweep net in spider collection. ©AMNH
The Sweep Net
This is a particularly simple way to catch spiders. The classic habitat for using a sweep net is one with grasses and flowers—a meadow. A sweep net is made of relatively heavy fabric, like sailcloth or canvas. It’s rugged enough not to be torn by the leaves and other vegetation that you usually wind up collecting along with the arthropods. It’s also tightly woven to catch spiders of relatively small size. To use a sweep net, drag the net back and forth across a low group of weeds and brush a number of times with a quick, steady motion. By sweeping the vegetation itself, you’ll end up catching organisms that live in and on the plants. Sweep as many times as necessary to get a good sample. Find out how to make your own sweep net.
The Beating Method
The beating method is good for sturdier vegetation, such as trees and shrubs. To begin, place a large tray, sheet, or upturned umbrella beneath the tree or shrub. Next, firmly tap the plant with a stick. Check your sheet quickly after beating to collect any spiders that may have fallen before they get away.
The Aspiration Method
A final, extremely precise and effective method is the aspiration method. The aspirator is a small glass vial topped with a rubber stopper that has two tubes emerging from it. One long flexible tube extends from the vial to your mouth. The other short, solid tube extends from the vial to your spider quarry. Through strong inhalation, the spider is literally sucked into the vial. Don't worry! It is not going to travel up the other tube and into your lungs! There is a small screen in the inhalation tube. This method is often used in conjunction with one of the other collection methods, such as beating, in order to get the spiders into collection containers. Once in the glass vial, you may study the spider live, or follow the steps below to preserve your spider.
|Vlad collects spiders by shaking bushes in Van Cortland Park, New York. ©AMNH
Collecting by Hand
One of the best methods to collect spiders is by hand. A soft paintbrush or cotton swab can be used to gently knock the specimen into a collecting vial, or you can gently pick specimens off by hand. Turning over stones and logs exposes many spiders, and hand collecting is the method of choice. Also check any webbing left under the stones for spiders hiding there.
The Berlese Funnel
If your site is in or at the edge of a forest, leaf litter (fallen leaves, sticks, twigs, etc.) will yield a rich harvest. That’s where the greatest diversity of terrestrial arthropods, including spiders, lives. Typically, in woodland you’ll get several thousand individual organisms out of a square-meter site. You can construct your own Berlese funnel device using a large coffee can with a plastic funnel inside and a metal grid over the top. Put the litter on top of the grid and cover it with another coffee can with a light in it. After a few days, the heat and the dryness will force the arthropods down the funnel and into your collection container with alcohol.
Most of what you collect will be very small, such as soil mites and springtails. Use a paintbrush to remove the tiniest spiders from the collection container. You will need a magnifying device and a light source to sort this material.
|Vlad digs a hole for a pitfall trap. ©AMNH
The Pitfall Trap
This is a wonderful method for catching ground-living spiders. The pitfall trap method catches spiders that you won’t catch in any other way. You can make your pitfall traps by digging round holes with a bulb planter or trowel and placing a plastic cup in each. The hole should be deep enough so the rim of the cup is level with the ground. Pour about an inch of water with a drop of liquid laundry detergent (or coolant) into each cup. Just so you know, researchers use propylene glycol (environmentally friendly antifreeze). The specimens will rot if you leave them for more than two or three days. If you want to collect live specimens, do not use any liquid in the cup. Check the cups every 24 hours and remove the specimens that have fallen into your traps.
Preservation of Spiders
Once collected, spiders can be identified from either live or preserved specimens. As a rule, identification of live spiders requires a significant amount of experience, so I encourage you to study preserved specimens first. If you want to study living specimens, be sure to research some information on how to design a habitat for your collection.
To preserve your spider specimen, place it in a petri dish and add 75% alcohol, taking care to completely cover the spider. Alcohol prevents spiders from drying out and anatomical parts, such as trichobothria, claws, and the setae on the legs, are easy to see in wet preserved specimens. It is very easy to identify freshly preserved spiders because all their coloration is still distinct. You should also be able to manipulate all the spider's legs.
People often ask me, "Do we have to kill spiders for research purposes?" I respond that most spiders live for only one year and the number of species in nature is tremendous. As we will only take a few specimens for our research, we will have a less than negligible effect on the spider population.