Insects are small. Therefore it is not easy for them to find each other by just looking around. Instead they have developed other ways to find each other: sound and smell. Some insects find each other by making special sounds that they can recognize. Others find each other by using smell.
Insects make sounds
There are many insects that can make sounds. They don’t have vocal chords like people but they have other ways of producing sounds. Some do it by rubbing body-parts together. Some have special organs to produce sound.
Male crickets make sound (sing) with their wings. By rubbing a sharp edge (the scraper) at the base of one front wing along a file-like ridge (the file) on the bottom side of the other front wing they can produce a chirping sound.
Male cicadas have special organs to produce sound. These are called tymbals. Inside the tymbal there are membranes that can vibrate to produce a "singing" sound.
Sounds that are produced by insects can have several meanings. One reason to make noise is to attract individuals of the other sex for mating. Other reasons to make sound are for fighting and for sounding an alarm.
Insects release odors
Many insects communicate with each other by using smell. They can release odors from special scent glands in their body. These odors are called pheromones.
In most species the females can produce a very specific smell to attract partners for mating. These odors are called "sex pheromones". Insects use their antennae to detect odors. In species where the female produces an odor, the males often have extra big antennae which help them to find the female.
Odors are also used for other reasons. For example ants use odors to mark a trail, so that other ants can use the trail to get back to the nest or to find food.
Some insects use smell to warn each other for danger. These odors are called "alarm pheromones".