Cousins

In the early morning light, an ant discovers a feast amid the desert of a tile kitchen floor. It hurries back to its nest mates, leaving a chemical trail for them to follow. By the time the home's occupants get up to have breakfast, a trail of hundreds of ants winds its way across the floor with a second trail branching off to explore the counter. A pest control professional is called to come to the aid of the homeowner. But when he arrives, the ants are no longer visible, having retreated back to the nest.

The PCO knows from experience that ants often trail under the edge of carpets in rooms adjacent to the area where they were originally seen. Here he finds several ants. Upon first glance, they appear to be fire ants, which are common in his area. He knows that fire ants often forage indoors from outside nests. He feels this may be the case because the wall where all the ants have been seen is an interior wall. Upon inspection outside, however, he can't find any fire ant mounds next to or near the foundation. He treats the trail of ants inside and spreads fire ant bait around the foundation.

A week later the homeowner calls to report that the ants are still present. The PCO arrives first thing in the morning and gets to observe an active trail on the floor. Close observation shows two sizes of workers, one of which has a huge head big headed ants. This ant commonly nests next to building foundations in the cracks between the soil and the foundation. It will also nest inside potted plants and in planter boxes outside. Inspection outside reveals a colony of big headed ants in and under a large potted plant on the porch near the back door. The ants were foraging at the time from the soil in the pot through a crack near the back door and from there into the kitchen.

The lesson in this story is that positive identification of ant species is very important to success in controlling an infestation. The minor workers of big headed ants closely resemble fire ant workers. Knowing the correct identity of the ant in question would have saved the above pest management professional an extra trip because he may have inspected different potential harborages for the infesting colony.

This article will examine the differences between ant species that closely resemble one another. Once these differences are known, they are easily recognized in the field.

MAGNIFIERS & VIALS. Because ants are so small, it is important to have a portable 30× magnifier available at all times. An excellent lighted magnifier can be purchased for about $10 from stores such as Radio Shack.

Pest management professionals should always carry vials filled with 70% isopropyl rubbing alcohol for collecting specimens. It is nearly impossible to observe the identifying characteristics of a live ant even using a magnifier. Ants must be killed in alcohol and then placed on a white sheet of paper for observation.

The easiest way to collect ants into a vial is to wet a finger with alcohol by holding the fingertip on top of the vial and then turning the vial upside down. Touch the wet fingertip to an ant, return the part of the fingertip holding the ant to the vial, and swirl the ant off the finger.

When making the identification in the field, it is quicker to take the ant captured on the fingertip and place it on a piece of white paper. Add a drop of alcohol to speed the demise of the ant. Once dead, the ant may be easily observed.

• Carpenter Ants vs. Field Ants. Carpenter ants (genus Camponotus) come in several colors from black to red and black to light brown, depending on the species. Field ants (genus Formica) also come in similar colors and include the black field ant and the Allegheny mound ant. Most carpenter ant species have large workers of several different sizes in the colony, while most field ant species are large ants of about ³/₈ inch in length.

These ants can easily be confused with one another, but they have widely varying nesting habits. Carpenter ants are partial to moist wood and voids and commonly nest inside buildings. Field ants are mound-building ants that prefer to nest in the soil in lawns and under items lying on the ground. They may forage in a building, but they rarely, if ever, locate a nest inside.

Both carpenter ants and field ants have a single node in their pedicel between the thorax and the abdominal gaster. Both also have a circle of tiny hairs ringing the anus at the tip of the abdomen. The key difference in the two ants is the shape of the thorax when viewed from the side. The carpenter ant's thorax is evenly rounded while the field ant's is uneven in shape (see Figure 1). Because these ants are so large, this characteristic can be observed in live ants by capturing a specimen and holding it by the legs in order to observe the thorax from the side.

• Carpenter Ants vs. Velvety Tree Ants. In the western states, California in particular, the velvety tree ant can be found in areas where carpenter ants are also found. Both of these ants have one node and both have an evenly rounded thorax. Both ants will nest in trees; the velvety tree ant, however, will also nest in the soil under stones and logs.

Carpenter ants have a circle of hairs ringing the anus; velvety tree ants do not. Carpenter ants have many sizes of workers, a number of which are large. The workers of the velvety tree ant are all one size and are small to medium-sized, ranging from ¹/₈ inch to ¼ inch depending on the species. The key visible difference is the velvety tree ant's shiny, black velvety abdomen, coupled with a reddish thorax and a darker head.

• Argentine Ants vs. Odorous House Ants. Where Argentine ants are common, they tend to be the dominant ant. But there are situations in which Argentine ants and odorous house ants will overlap in a given town or neighborhood. Both ants are small and brown with workers all of one size. Both develop large colonies and are opportunistic in choosing nesting sites, and both readily infest structures. Argentine ants, however, can be found nesting throughout a building, even in the insulation of the attic and the walls. Odorous house ants usually have a large component of their colony located outside with smaller satellite colonies located inside.

These two ants are easy to tell apart by examining the pedicel area between the thorax and abdomen. Although both ants have only one node, the Argentine ant's node is sharply pointed and is clearly visible. The node of the odorous house ant is flattened and is hidden by the abdominal gaster (see Figure 2). The Argentine ant has a shiny appearance while the odorous house ant is a dull brown. The odorous house ant also gives off a rotten coconut-like odor when crushed.

• Pharaoh Ants vs. Thief Ants. This is probably the pairing of ants that is most commonly confused by pest management professionals. Both ants are some shade of yellow in color and both have two nodes. The thief ant is smaller, but the size difference is only noticeable if you have both ants side by side, so this is not a reliable identifying characteristic to use in the field.

The key to identifying these two ants is by examining the antennae. Pharaoh ants have 12 segments in their antennae, including the long first segment, and the antennae end in a three-segmented club. A thief ant's antennae have only 10 segments and they end in a two-segmented club. Thief ants also have a stinger that may or may not be extended and visible under magnification.

• Fire Ants vs. Big Headed Ants. These two ants are not often confused with each other, but in certain situations, misidentification can occur. Usually, the minor workers of big headed ants are observed and are assumed to be fire ants. Both ants are reddish brown in color and both have two nodes. The easiest way to distinguish between the two ants in the field is to observe the trail and compare the sizes of the workers. When dealing with big headed ants, look for all the minor workers to be the same small size. If you are patient, a large-headed major worker will soon appear in the trail. Fire ants have a number of different worker sizes, ranging from very small to ¼ inch or larger.

If only a single specimen is available or specimens are brought in from the field, identification under magnification is necessary. Fire ants, like thief ants (both belong to the genus Solenopsis), have only 10 segments in their antennae, and the antennal clubs have two segments. The antennae of a big headed ant has 12 segments and ends in a three-segmented club. The fire ant also has a stinger at the tip of the abdomen; the big headed ant has no stinger. Big headed ants have a pair of spines on the top rear part of the thorax and the fire ant has no thoracic spines.

CONCLUSION. Ants are among the most difficult structural pests that a pest management professional is asked to identify. Most ants are small and are reddish brown or brown in color, but their biologies can be varied, so correct identification is important. Proper training in ant identification requires having a microscope available in the office where a trainee can clearly see the identifying characteristics he or she will be asked to look at in the field with a less expensive magnifying device.

Collect specimens of all structure-infesting and species in your area and train new employees on the identifying characteristics of each. Retrain all wervice and sales personnel regularly to refresh their memories. Equip each person with a good ant identification guide, such as the PCT Field Guide to Managing Structure-Infesting Ants or the NPCA Field Guide, to carry in the service vehicle.

It costs valuable time and money for service professionals to bring ant specimens back to the office for identifications that could be done on-site in the field. Training, good magnifying devices and reference materials are the keys to correct ant identifications.