Pass it on
Pheromones get the message across
Hormones carry messages between cells in the same organism. Pheromones carry messages between individuals of the same species. The same types of chemicals tend to be involved, including peptides and proteins, the latter most often as receptors.
Insects often use small, volatile molecules as pheromone messengers because they can travel relatively long distances in the air. Protein and peptide pheromones are much more common among bacteria, where they are effective messengers in solution, and pass between cells.
Bacteria release pheromones as an aid to conjugation (when bacterial cells link to transfer DNA), and many use the concentration of particular pheromones as an index of the local population density.
This is useful in quorum sensing, where a colony of bacteria behaves in a particular way if enough bacteria are nearby. For example, a bacterium that lives in marine creatures will make a glowing chemical only when individual bacteria have detected that there are enough other bacteria nearby for the emitted light to be visible.