Collecting can be as simple as picking up stray ants and placing them in a glass jar or as complicated as completing an exhaustive survey of all species present in an area and estimating their relative abundances. The methods used will depend on the final purpose of the collections. For taxonomic studies, long series from a single nest which contain all castes (workers, including majors and minors, and if present, queens and males) is desirable to allow the determination of variation within species. For ecological studies, the most important factor is collecting identifiable samples of as many of the different species present as possible. Unfortunately, these methods are not always compatible, with the taxonomist sometimes overlooking species in favour of those groups currently under study and while the ecologist often collects only a limited number of specimens of each species, thus reducing their value for taxonomic investigations. To collect as wide a range of species as possible, several methods should be used. These include hand collecting, using baits as attractants, ground litter sampling, and the use of pitfall traps. For a general overview of collecting methods, see Upton (1991).
- 1 Collection Methods that mix workers from different ant nests
- 2 Collection Methods that find ant nests and retrieve nest series
- 3 REFERENCES
Collection Methods that mix workers from different ant nests
Baits can be used to attract and concentrate foragers. This often increases the number of individuals collected and will sometimes attract species that would be difficult to locate otherwise. Sugars and meats or oils will attract different species and both should be utilised. Honey is a good sugar source while tuna or cat food are readily available and inexpensive meat sources. These baits can be placed either on the ground or on the trunks of trees or large shrubs. When placed on the ground baits should be situated on small paper cards or other flat, light-coloured surfaces, or in test tubes or vials. This makes it easier to spot ants and to capture them before they can escape into the surrounding leaf litter.
Leaf Litter Sifting
Many ants are small and forage primarily in the layer of leaves and other debris on the ground. Hand collecting these species can be difficult. One of the most successful ways to locate these small, cryptic foragers is to collect the leaf litter in which they are foraging and extract the ants from it. This is most commonly done by placing leaf litter on a screen above a large funnel, often with a heat source above the leaf litter (a Berlese funnel). As the leaf litter dries from above, ants (and other animals) move downward and eventually fall out the bottom and are collected in alcohol placed below the funnel. This method works especially well in rain forests and wet sclerophyll areas. A method to improve the catch when using a funnel is to sift the leaf litter through a coarse screen before placing it above the funnel. This will concentrate the litter and remove larger leaves and twigs. It will also allow more litter to be sampled when using a limited number of funnels. A similar appraoch for processing leaf litter in the field where the heat source is the sun is to use a Winkler Sifter. The leaf litter is first sifted and then placed in the top section of a closed hanging bag. The sun then gradually warms and drives the ants down to the lower section of the bag where they drop into a container of alcohol. The combined ants, insects, mites and debris must be sorted a second time.
The pitfall trap is another commonly used tool for collecting ants. A pitfall trap can be any small container placed in the ground with the top level with the surrounding surface and filled with a preservative. Ants are collected when they fall into the trap while foraging. The diameter of the traps can vary from about 18 mm to 20 cm and the number used can vary from a few to several hundred. The size of the traps used is influenced largely by personal preference (although larger sizes are generally better) while the number will be determined by the study being undertaken. The preservative used is usually ethylene glycol or propylene glycol (safer), as alcohol will evaporate quickly and the traps will dry out. If specimens will not be needed for long-term storage, automobile anti-freeze can be used successfully, although the dyes used may discolor some specimens. One advantage of pitfall traps is that they can be used to collect over a period of time with minimal maintenance and effort. One disadvantage is that some species are not collected as they either avoid the traps or do not commonly encounter them while foraging.
One useful technique is to place a second cup inside of the first cup. Then once the inside cup and ants are removed, a second inside cup can be used to replace the first. The inside cup can be easily cleaned of falling soil when the pitfall trap is first constructed and before liquid is poured inside. Pitfall traps should be checked every 24 hours to make sure that they have not been disturbed. If pitfall traps are checked in the evening and then in the early morning, nocturnal ants can be separated from diurnal ants.
Hypogaeic (Subterranean) ants are a diverse assemblage of species that are difficult to study and collect. Several methods have been designed to capture ants from below the surface in both tropical and arid regions. One method is a hypogaeic pitfall trap designed by Schmidt and Solar (2012).
Beating Low Vegetation
In this method it helps to have an assistant although one person can complete the task. Basically a given number of wacks are applied with force to low hanging vegetation while a "beating sheet" is placed below to catch falling items. Often leaves, spiders and other organisms fall onto the heads and shoulders of those below the branches so this is a technique commonly done during the day. Ants are picked off the the sheet using a pooter or forceps or fingers and placed into alcohol. Some ants are quick to escape the sheet while others may stay within cavities of the branches.
This is an elaborate method to collect ants from the upper canopy. Used a heat generator, a pesticide (usually a synthetic pyrethroid or natural pyrethrin) is volatilized as a fog (mixed with an oil based solvent)below an emergent tree early in the morning before wind currents distrupt the process. A number of capture nets or sheets are placed below the tree and searched for dropping ants. A large bulk of insects and other animals may drop below.
Although it is tempting to grab many different individual foragers and collect them into a common vial this method has the common outcome of loosing valuable information on nest size, location, colony structure and behavior.
Malaise Traps and yellow pan traps
Collecting ant reproductives (winged females and males) can be a goal. Determining the presence of army ants, and other subterranean ants by initially collecting the winged forms may be a first step in eventually finding colonies. With molecular techniques including DNA bar coding, males can now be associated with females and workers of a given species for the first time.
Collecting at Lights
Similar to Malaise traps and yellow pan traps, light traps primarily collect winged reproductives including both males and queens. Light traps provide locality information as well as good data on reproductive flight periods even abundance data. Often the best hours to run a light (black light or mercury)are just before nightfall. Temperatures must be warm enough for flight to occur and visiblilty is improved if the light source is elevated about the surroundings. You can even hoist a light trap up into a tropical tree to improve visibility.
Collection Methods that find ant nests and retrieve nest series
When possible, members of a single nest or foraging column should be kept together. This will assist later when determining the amount of variation within a species and helps associate workers with queens and males (when present). Similarly, pitfall or bulk-collected material should be labelled so that extra care can be taken to determine if several similar species are present or if there is only a single, variable species. One commonly used method to associate members of a single collection is to assign it a sequential number. Using this system is helpful because it reduces the time needed to label individual tubes in the field, can be used to cross reference field notes with specimens, provides information on which individuals are from the same nest or foraging column, and can be used to associate specimens stored on pins and in alcohol (see Specimen Preparation).
Hand collecting consists of searching for ants everywhere they are likely to occur. This includes on the ground, under rocks, logs or other objects on the ground, in rotten wood on the ground or on trees, in vegetation, on tree trunks and under bark. When possible, collections should be made from nests or foraging columns and at least 20 to 25 individuals collected. This will assure that all individuals are of the same species and increase their value in detailed studies. Since some species are largely nocturnal collecting should be done at night as well as during the day. Specimens are collected using an aspirator (often called a pooter), forceps or a fine, moistened paint brush, or with fingers if the ants are known not to sting (unless, of course, the collector enjoys pain). Individuals are placed in plastic or glass tubes (1.5 - 3.0 ml capacity for small ants, 5 - 8 ml for larger ants) containing 75% to 95% ethanol. Plastic tubes with secure tops are better than glass because they are lighter and do not break as easily if mishandled.
Lloyd Davis has developed a sifter for leaf litter that can be used in the field to collect small colonies of leaf litter ants. The sifter comes in two parts, a screened cover and a smooth basin. The leaf litter is first sifted through the screen and then the ants are picked out of the basin below. Previosuly ant collectors would bring the leaf litter back to a base camp and sort through the material which was now all mixed together. The Davis Sifter is an excellent tool to use to pick up fast moving ants by tossing them along with a small amount of debris and then collecting them individually as they fail to escape from the steep slippery slope of the sifter. It is better for your lungs to poot ants from the basin of a Davis Sifter where there is less soil and dust. A special use for the Davis Sifter is when you are sifting through a large Formica ant mound looking for ant social parasites.
Breaking Twigs and Chopping into Coarse Woody Debris
In the tropics and subtropics many rare ants nest in small twigs and chunks of wood burried in and below leaf litter. A large series of twigs can be collected and then opened later over a sorting pan (Davis Sifter). Complete nest series of many ant species can be collected using this method. Chopping into wood is more difficult and time consuming. In some cases trees can be climbed and dead branches pulled to the ground and searched for ant nests. Wood and logs already on the ground in various stages of decay are an excellent medium to search for ants. When termite nests are found in the wood, be sure to check carefully for associated ants.
Artificial Nests and Subterranean Probes
A subterranean probe is a method that uses an auger to drill a hole down into the soil in preparation for a sleeve containing bait.
Artificial twig nests and other cavity nests can be effective in collecting entire colonies of many ant genera and species in both temperate and tropical habitats. Care should be taken so that after a given period of time the artificial nests can be retrieved for inspection without loosing the location.
Special Microhabitat Collection Methods
There are a few ant species that nest in unusual habitats such as inside of hollow plant stems, in acorns and hickory nuts, under the bark of standing tree, arial gardens, termite mounds, hardwood logs, and in the nests of other ants (social parasites). Each of these habitats require special techniques in order to find and collect ants. Some ants are even found in semi-aqatic zones such as in mangrove swamps, deep in bogs, and in coral reefs close to shore. There are a few ants that mimic other ants so closely that their identity is not discovered until they are viewed under a microscope.
- Abensperg-Traun, M. and Steven, D. 1995. The effects of pitfall trap diameter on ant species richness (Hymenoptera: Formicidae) and species composition of the catch in a semi-arid eucalypt woodland. Australian Journal of Ecology 20: 282-287.
- Andersen, A. N. 1991. Sampling communities of ground-foraging ants: pitfall catches compared with quadrat counts in an Australian tropical savanna. Australian Journal of Ecology 16: 273-279.
- Bestelmeyer B.T., Agosti D., Alonso L.E., Branda˜o C.R.F., Brown W.L., Delabie J.H.C. and Silvestre R. 2000. Field techniques for the study of ground dwelling ants. An overview, description, and evaluation. In: Ants: Standard Methods for Measuring and Monitoring Biodiversity (Agosti D., Majer J.D., Alonso L.E. and Schultz T.R., Eds), Smithsonian Institution Press, Washington London, pp 122-144
- Borgelt, A., and New, T. R. 2005. Pitfall trapping for ants (Hymenoptera, Formicidae) in mesic Australia: the influence of trap diameter. Journal of Insect Conservation 9:219–221.
- Borgelt, A., and New, T. R. 2006. Pitfall trapping for ants (Hymenoptera, Formicidae) in mesic Australia: what is the best trapping period? Journal of Insect Conservation 10: 75–77.
- Greenslade, P. J. M. 1973. Sampling ants with pitfall traps: Digging-in effects. Insectes Sociaux 20: 343-353.
- Upton, M. S. 1991. Methods for collecting, preserving, and studying insects and allied forms. 4th ed. Brisbane, Queensland: Australian Entomological Society. 86 pp.