Collecting Ants

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 must 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 (1992).

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.

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.

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.

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 10 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, 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 discolour 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. For further discussion on the use of pitfall traps, especially in ecological studies, see Greenslade (1973), Andersen (1991), Abensperg-Traun and Stevens (1995) and Borgelt and New (2005, 2006).

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).

Literature Cited/Additional Reading 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. 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.