California Beetle Project > Fieldwork > Collecting Methods
Assembling a complete inventory of beetles of an area requires a great diversity of techniques. While individual species generally have very specific habits, together beetles are highly varied. Some are terrestrial, while others are aquatic. Some species are flightless while others are agile aerialists. Few single collecting methods will yield more than a small fraction of what occurs in a given area. Our protocols include several types of traps, employed to sample continuous periods ranging from a few days to several months, as well as a variety of 'direct sampling' techniques. This page describes some of the most productive of these.
Probably the most productive in terms of total beetle diversity is the flight interception trap. This trap takes advantage of the tendency many beetles have of dropping when flying into a barrier. A mesh 'window', a couple meters square, suspended tightly over preservative-filled pans, intercepts beetles in flight, which then fall into the pans below.
The Malaise trap operates by the opposite principle, collecting species whose instinct is to grab onto and attempt to climb over barriers. The trap is an open sided tent, funnelling insects to a collecting jar at the apex. Though Malaise traps do not collect great numbers of beetles, being more productive for flies and wasps, they do tend to collect unusual species.
Pitfall traps are a beetle collecting standard. A simple cup or small bucket buried up to its rim in the ground, pitfalls collect primarily ground active beetles, especially ground (Carabidae) and darkling beetles (Tenebrionidae). Pitfall traps may be baited with various attractants. We frequently use rotting meat, rotting fruit, dung, and cantharidin, each of which attracts a small subset of specialized beetles. Unbaited pitfalls rarely collect large numbers of beetles, but over time, they generally also result in an interesting diversity of species.
Lindgren funnel traps have long been used by forest entomologists to sample bark and other wood boring beetles, but are less often used in biodiversity surveys. Their vertical profile of nested funnels is apparently viewed as a potential host tree by beetles. Lures of compounds associated with tree decay, such as turpentine and ethanol, as well as beetle pheromones, are frequently used to enhance their attractiveness for certain species.
Many nocturnal beetles are attracted to light, particularly light with a strong ultraviolet component. Blacklights and mercury vapor lights set up in front of white sheets attract a diverse sample of beetle species. Light collecting in California rarely attracts the overwhelming abundance of insects one finds in more humid parts of the country, but the species diversity attracted on a warm, early summer night can be impressive.
Beyond these basic techniques, there are as many direct collecting methods as there are collectors. Only a few of these are covered here. One of the most productive includes 'beating' the foliage of all kinds of plants, living and dead. Some of our flowering shrubs, such as elderberry (Sambucus) and Ceanothus attract huge numbers of beetles when in bloom. The bark of dead trees, particularly oaks, firs, and pines, hides many interesting beetle species. Many beetles are found only along stream margins, and 'washing' their banks can turn up some interesting things. Stream pools and other areas that stay moist into late summer, as other streams dry up, can be exceptionally productive. Many such riparian species are nocturnal, and not attracted light, so searching stream banks by flashlight often turns up unusual beetles.