9.
Many species of ants lay chemical trails when they search for food. Once one ant
discovers food and returns to the colony, other ants follow its trail back to the food
source. Once the food runs out, ants abandon the trail and begin to search for new food
sources. For this process, ants should use signal molecules with which of the following
properties?
a. Species-specific chemical, half-life of one day
b. Common chemical, half-life of one day
c. Species-specific chemical, half-life of one hour
d. Common chemical, half-life of one hour

Ants Chemical Trails: Ideal Signal Molecule Properties for Foraging

Ants use chemical trails called pheromones to guide colony members to food sources efficiently. These trails must evaporate quickly once food depletes so ants search anew. The correct properties balance specificity and transience.​

Option Analysis

a. Species-specific chemical, half-life of one day
This fails because a one-day half-life keeps trails active too long after food runs out, causing ants to revisit depleted sites instead of foraging elsewhere.​
Species-specificity is good to prevent other species interference, but persistence mismatches the need for rapid abandonment.​

b. Common chemical, half-life of one day
A shared chemical invites rival species to exploit the trail, risking food theft. Combined with long persistence, it worsens inefficiency for the colony.​
No ant species benefits from such vulnerability in competitive environments.​

c. Species-specific chemical, half-life of one hour
Species-specific pheromones ensure only colony members follow, avoiding kleptoparasitism. A one-hour half-life allows quick recruitment to fresh food while enabling abandonment when depleted, matching observed trail durations of minutes to hours.​
Studies confirm short half-lives (3-9 minutes in some species, up to 1 hour in others) support dynamic foraging.​

d. Common chemical, half-life of one hour
Short half-life works for transience, but non-specificity lets other ants hijack trails. Early research noted apparent specificity, but many trails show interspecies responses, though colony protection favors uniqueness.​

Correct Answer

c. Species-specific chemical, half-life of one hour drives effective foraging by securing trails for colony use with timely decay.​