Entomology: Types of Insects Traps

Trapping

Collectors use a variety of traps and trapping techniques to capture insects and other arthropods. These range from simple and inexpensive to elaborate and costly. Some are designed to collect certain insects that are rarely collected without a trap. Others are useful for general collecting. The traps and techniques described here are just a small sample of those available to the collector. A collector can invent new traps or modify old designs for unique purposes.

Bait trap

The addition of bait to many traps will attract large numbers of certain types of insects. Baited pitfall traps are common collecting devices. The bait is placed in the bottom of the collecting can and covered with a screen, or it is suspended into or over the trap. Dead animals, rotting foods, and dry cereals are good baits for various crawling insects. One type of pitfall trap, the cereal dish trap, is particularly effective for collecting insects attracted to dung. This trap is made from a cereal bowl filled with 70% ethanol and sunk into the ground. The bait is suspended in a small cup over the trap, supported by a wire coat hanger.

Barrier Trap

When insects hit a barrier in their flight path, they tend to fly upward or drop. Barrier traps placed in flyways rely on such behaviors to capture flying insects. One simple barrier trap is the windowpane trap, which consists of a piece of clear glass or plastic with a shallow trough filled with 70% ethanol attached at the bottom. When the trap is hung across a path, in a flyway, or at the edge of the woods, flying insects crash into it. Those that drop after hitting the glass fall into the trough and are killed.

Emergence Trap

Immature insects live in a wide range of habitats, including plant stems and roots, galls, rotting logs, decaying vegetation, soil, and water. When these insects emerge as adults, they can often be captured in an emergence cage. The cage can be as simple as a net sleeve over a tree branch or a screened box placed over a patch of soil.

Light Trap

Light traps provide a good method for collecting large numbers of night-flying insects or for collecting insects from several locations at once. They are also a valuable tool for individuals who cannot be out at night to collect.

The simplest light trap consists of a UV light (often called a black light) and a collecting pan with alcohol covering the bottom. The pan is placed below the light, and insects flying toward the light eventually drop into the alcohol. When set up near a stream or lake, this trap is very effective for collecting the winged adults of many aquatic insects. Commercial light traps of various designs are also available. Most of these consist of a light source, a series of baffles, a funnel, and a killing jar. The jar usually contains alcohol as the killing agent.

Malaise Trap

Another, more elaborate trap is the malaise trap, which captures flying insects that move upward when they strike a barrier. This trap is a tentlike structure made of netting with a collecting chamber at the top. Insects entering the trap eventually fly or crawl upward while attempting to escape. Instead of escaping, they become trapped in a killing jar or a container of ethanol. Malaise traps can be purchased from commercial suppliers or constructed at home. A dark fabric is recommended for the base. Malaise traps placed across paths or alongside streams, woods, or sheltered clearings frequently yield good catches. Also, when selecting a site, it is best to keep in mind that most insects fly upward.

Pitfall trap

Insects that crawl about on the ground can be captured in a pitfall trap. The simplest trap can be constructed easily by placing a can or plastic container in the ground. Add enough killing agent (such as alcohol) to cover the bottom of the container. To keep rainwater out of these traps, a board can be propped up over the opening.

Snap Trap

Two kinds of traps designed for quantitative sampling may be termed “snap traps.” It consists of a pair of wooden or plastic discs, slotted to the center so as to fit on a tree branch and connected to each other by a pair of rods. A cloth cylinder is affixed at one end to one of the discs and at the other end to a ring sliding on the rods.

After the cloth cylinder has been pulled to one end and has been secured in place, the ring is held by a pair of latches. When insects have settled on the branch, its leaves, or flowers, the latches are released by pulling on a string from a distance, and the trap is snapped shut by a pair of springs on the rods, capturing any insects present. One of the canopy traps operates in a similar fashion. When a remotely controlled latch is pulled, a spring-loaded canopy is snapped over an area of soil, and insects within the canopy are collected by suction or a vacuum device. This trap was designed for use in grasslands.


Sticky Trap

In this type of trap, a board, piece of tape, pane of glass, piece of wire net, cylinder, or other object, often painted yellow, is coated with a sticky substance and suspended from a tree branch or other convenient object. Insects landing on the sticky surface are unable to extricate themselves. The sticky material is later dissolved with a suitable solvent, usually toluene, xylene, ethylacetate, or various combination of these, and the insects are washed first in Cellosolve and then in xylene.

This type of trap should not be used to collect certain specimens, such as Lepidoptera, which are ruined by the sticky substance and cannot be removed without being destroyed. Various sticky-trap materials are available commercially, some with added attractants. However, use caution in selecting a sticky substance because some are difficult to dissolve.


Emergence and Rearing Trap

New Jersey Trap

An emergence trap is any device that prevents adult insects from dispersing when they emerge from their immature stages in any substrate, such as soil, plant tissue, or water. A simple canopy over an area of soil, over a plant infested with larvae, or over a section of stream or other water area containing immature stages of midges, mayflies, and other arthropods will secure the emerging adults. If it is equipped with a retaining device, as in the Malaise trap, the adults can be killed and preserved shortly after emergence.

It must be remembered, however, that many insects should not be killed too soon after emergence because the adults are often teneral or soft bodied and incompletely pigmented and must be kept alive until the body and wings completely harden and colors develop fully. Emergence traps and rearing cages enable the insects to develop naturally while insuring their capture when they mature or when larvae emerge to pupate.



Windowpane Trap

One of the simplest and cheapest traps is a barrier consisting of a windowpane held upright by stakes in the ground or suspended by a line from a tree or from a horizontal line. A trough filled with a liquid killing agent is so placed that insects flying into the pane drop into the trough and drown. They are removed from the liquid, washed with alcohol or other solvent, then preserved in alcohol or dried and pinned. The trap is not recommended for adult Lepidoptera or other insects that may be ruined if collected in fluid.

A modification of this trap uses the central "pane" of a malaise trap instead of a pane of glass. The malaise trap pane covers more space than glass, is easier to transport, and, of course, is not breakable. Various mesh sizes if cloth can also be used depending on the insects targeted. These traps may also be referred to as flight intercept traps.


Tullgren Funnel

The Berlese or Tullgren funnel and its modifications are cleaner and more efficient than sifting to separate insects and mites from leaf mold and similar materials. The sample (usually presifted to remove large debris) is placed on a screen near the top of a funnel. A light bulb can be placed above the sample to produce heat and light, which drive the insects downward into the funnel, or heated coils or a jacket around the funnel can be used to dry the sample and make it inhospitable.

The insects and mites are directed by the funnel into a container, sometimes containing alcohol at the bottom of the funnel. Care should be taken not to dry the sample so rapidly that slow-moving specimens are immobilized before they can leave the sample. To prevent large amounts of debris from falling into the container, place the sample on the screen before the container is put in place.

Flight intercept trap

The most common passive, flight-intercept trap is the Malaise trap (Figure 1). The one used in this inventory is modeled after the description given by Townes (1962). For a complete review on Malaise traps see Steyskal (1981). Malaise traps work on the principle that many flying insects fly to the highest and brightest point (collecting head) when they encounter an obstacle (trap panels). This is a particularly effective method for collecting Diptera and Hymenoptera. A liquid-filled trough or pitfall should be placed along the base of the central wall to collect species that drop when they hit a barrier (e.g., many Coleoptera).

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