Biological Sciences, Santa Barbara City College pipeline center for sustainability

Biology 130: Methods in Field Biology

Field Technique:  Insect and Spider Surveys

Insect surveys present numerous challenges. First, there is great diversity among insects making identification to species difficult. Second, they are generally small and many species are camouflaged and inconspicuous or have life stages that are difficult to find and identify. Third, many may be active at times when they are difficult to observe. Finally, to identify and quantify species in an area may require collecting the insects which can negatively affect the wild population.

Photography is being used in some cases to identify species without harming them, but it is likely not going to be useful for determining abundance unless you can photograph large groups at once and prevent double counting. Taking a good quality photograph that allows identification is also not trivial. This may make the technique prohibitively difficult for many species. Even species that may be easy to identify from a photo may not be cooperative. They could be fast moving, shy, or live in areas where photography is challenging (rainy environments, caves, etc.)

Bumble Bee Watch is a Citizen Science project organized by the Xerces Society that uses photography to contribute to our understanding of the range of native bee species.

 

bumble bee on manzanita

bumble bee on manzanita

bumble bee on manzanita

 

Not all species of insects visiting flowers are bees, even if they look like them.

 

bee fly on manzanita

fly on manzanita

 

Sampling using photography can also introduce bias. Some species will simply be easier to photograph than others. This can skew your results in favor of the more easily photographed species even if they are not more common.

If you were to use photographs to estimate abundance then individual variation in behavior can introduce bias. Nature photographers know that there are certain individuals that are less shy and will allow a closer approach. This could easily result in double counting an individual or skewing mark re-capture/re-site results. The same thing can happen when trapping and releasing animals because some can become "trap happy" or "trap shy." Trap happy animals will get re-trapped more than would be random (for example, a small mammal may "like" getting trapped because it gets a free meal), and trap shy individuals will avoid a trap. This presents challenges to coming up with an accurate estimate.

 



Many insect species are not so easily seen as with bees or flies visiting showy flowers during the day. This means different methods may be required to just get a look at them.

 

spider sampling
(Sampling spiders from leaf litter. Photo by Adam Green)

Pan Traps collect insects atracted to a water filled pan. Thuis study evaluated the efficacy of different locations and colors of pans:

Pan trapping proves to be an effective method for field surveying insects, especially Diptera. This manuscript examines the effectiveness of the method for the rapid bioinventory of freshwater shoreline insects. Pan traps at ground level, above ground, and elevated and of different colors were evaluated for their ability to attract and capture insects. Abundance (n), taxonomic richness (T), and hierarchical diversity indices (H′) allowed for the determination of efficacy among methods. Yellow pan (n = 141, T = 10, H′ = 1.15) and elevated yellow pan traps (n = 113, T = 5, H′ = 1.18) were most effective at capturing the highest diversity of insects. Blue (n = 12, H′ = 1.18) and green (n = 51, H′ = 0.74) traps had similar richness (T = 4); however differed in the total insects captured and diversity. The results provide entomologists in South Texas and other subtropical environments with information to assist them with planning surveys in the field and with further study potentially developing pollution tolerance values for different insect taxa.

This study also compared different colors of pan traps and included malaise traps:

Pan and Malaise traps have been used widely to sample insect abundance and diversity, but no studies have compared their performance for sampling pollinators in forested ecosystems. Malaise trap design and color of pan traps are important parameters that influence insect pollinator catches. We compared pan trap (blue, yellow, white, and red) and Malaise trap catches from forests in three physiographic provinces (Piedmont, Coastal Plain, and Blue Ridge) of the southeastern United States. Similarities in trap performance between sites were observed with blue pan traps being most effective overall. Our results showed that various pollinator groups preferred certain pan trap colors and that adding color to Malaise traps influenced insect pollinator catches. However, pan traps generally caught more pollinators than Malaise traps. Because of their low cost and simplicity, using several colors of pan traps is an effective way to sample relative abun4ance and species richness of flower-visiting insects.

With many of these methods we have to collect and kill the insects or spiders to properly identify them. This may not be appropriate with endangered species, in areas where collecting insects may not be understood by the public (i.e. in a botanic garden), or where the sampling itself may affect estimates of abundance.

Nocturnally active species present another challenge. In some cases we can take advantage of characteristics that allow us to use some simple techniques to find and identify them. For example, the use of headlamps to find Wolf spiders at night because they exhibit eye shine.

night survey for wolf spiders
(Wolf spiders can be found at night using eye shine)

spider sampling
(Wolf Spider, likely pregnant. Photo by Adam Green)

Some species of spider use webs and materials that make them easier to locate and identify.

 

spiders
(Cyclosa sp., Trash line orb weaver, Funnel Web Spider using an old oak gall. Photos by Adam Green)

Funnel web spider
(Funnel Web Spider. Photos by Adam Green)

 

orb weaver spiders
(Orb weaver spider and webs, Rattlesnake Canyon, Santa Barbara, CA. Photos by Adam Green)

 

orb weaver spider
 

Many species of spider do not use webs and may be more difficult to find. Some can be caught using sweep nets, others are found by simply hunting in areas where they are likely to be found.

 

spiders
(Male Goldenrod crab spider Misumena vatia on Morning Glory flower, Big Creek reserve, Big Sur, CA., Crab spiders and Jumping spider, Photos by Adam Green)

 

Jumping spider
(Jumping spider Phidippus johnsoni, Photos by Adam Green)

 

Field spiders
(Spiders caught in a grassy field with dispersed shrubs, Big Creek Reserve. Photos by Adam Green)

 


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Revised 26 January, 2015
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