Volume 45, Number 4,
July 1999: Carpenter Ants

Text-only version

ISSUE HOME PAGE

ABOUT THIS ISSUE
- about KSN
- about the authors

IN THIS ISSUE

Section 1:
- introduction
- what is a carpenter ant?

Section 2:
- life cycle
- colony size

Section 3:
- how carpenter ants find their way around

Section 4:
- feeding habits
- optimizing feeding
- territorial ants go to war
- avoiding war

Section 5:
- why active at night?
- ecological value of carpenter ants

Section 6:
- surviving winter
- destroying wood
- contrast between termites and carpenter ants

- References

SLIDESHOW
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Carpenter Ants
by John H. Klotz, Laurel D. Hansen, Byron L. Reid and Stephen A. Klotz

HOW CARPENTER ANTS FIND THEIR WAY AROUND

Existing in an area with several different colonies and avoiding aggressive encounters requires carpenter ants to be familiar with their home range.  Since they are primarily nocturnal, they rely heavily on physical cues and chemical trails for orientation to and from the nest. Well-maintained physical trails and trunk lines of carpenter ants serve as roadways through vegetation and debris (Figure 4). These trails are reminiscent of the wide, cleared trails of leaf-cutting ants, common to Central and South America.  In extreme northern latitudes, carpenter ant trails will often go underground following natural hollows, such as those left by decaying tree roots in the soil.  These tunnels are usually 1.5 to 3.0 centimeters in diameter and may be as deep as one meter below the earth’s surface.

Figure 4. Carpenter ants maintain large trunk lines.  One trunk line is shown below in a grassed area.

Figure 5. Carpenter ants forage at night on a oak tree using a "moon compass" for orientation.

Chemical trails consist of hydrocarbons produced in the hindgut of the ant and deposited on the trail surface.  These hydrocarbons are pheromones and are deposited by the ant when the tip of her abdomen is dragged on the substrate for short distances as she moves along the trail.  Pheromones are odorous compounds produced by the ant to convey information.  In the case of trail pheromones, the compounds guide ants to locations outside of the nest. Heavy deposits build up over time on heavily traveled trails forming "trunk trails" or main transportation arteries guiding foragers to resources.  Resources include aphid colonies where ants collect honeydew, a favored food rich in sugars and sought by many different ant species.

Trail pheromones also recruit nestmates to newly discovered food resources.Based on the relatively large size of the carpenter ant’s olfactory lobes located in the brain, the sense of smell is clearly important.  Smell serves the ants well in their nighttime activities.However, the individual forager eventually must leave the trunk trail to search for resources using both touch and sight, and to accommodate this, other orientation cues are used.

“Structural guideline orientation” is one such important cue for foraging carpenter ants.  Unlike the chemicals in odor tails, structural guidelines are tactile stimuli in the form of edges, grooves, or crestlines provided by tree bark, vines, branches, or roots on the forest floor.  Carpenter ants follow elaborate detours along branches or sidewalks rather than go in straight lines.  An ant’s movement is more efficient on smooth, uncluttered guidelines compared to movement along trails on the ground where turf and surface features impose numerous obstacles to the ant’s passage.  The benefit of these structural detours is the shortening of overall trip time.  Structural guidelines are the lowest level of cue found in investigations of carpenter ants’ orientation system.  If placed in total darkness, ants are unable to negotiate shortcuts by using visual cues and resort to tactile orientation along structural guidelines.  If total darkness is momentarily interrupted by an overhead view of the forest canopy or another visual cue, ants switch to another orientation method called landmark orientation.  Landmarks include any visually conspicuous object such as a tree or shrub. Landmarks are memorized in detail and guide ants to and from the nest.

Canopy orientation is one type of landmark orientation that carpenter ants use in temperate forests and under low light conditions of the night sky. Since carpenter ants nest within trees, the use of leaf canopy landmarks as cues may be an adaptation to increase the likelihood of ants returning to the nest tree after foraging.

Carpenter ants show a strong response to light at night.  This suggests that the moon is also used by carpenter ants as a directional cue (Figure 6).  Felix Santschi, a French entomologist, demonstrated sun compass orientation in desert ants in Africa in 1911. He reversed the direction of the sun using mirrors and showed clearly that desert ants do orient by means of the sun. A similar mirror experiment on moonlit nights gives similar results with carpenter ants. Foraging carpenter ants reverse their direction in response to a change in the apparent position of the moon caused by the introduction of mirrors.

Within the assemblage of orientation cues for carpenter ants, there is a built-in redundancy.  Foraging ants actually rely on more than one orientation cue; for instance, a forager uses an odor trail as well as a light source to orient.  As a consequence, the ants possess back-up cues with which they can orient in the absence of any one particular cue.  This arrangement provides carpenter ants with the ability to forage in the woodlands in daylight and total darkness (Figure 7).

Figure 7. Aphid colonies are tended by carpenter ants for honeydew.