Pheromones. Many insects use pheromones to leave markers where food is located or to lay down a path to food. You usually see this trait in social insects like ants and other very successful insect species. When I say successful, I mean abundant. Ants are abundant worldwide, as are most social insects like bees, termites, and some wasp species. Another group of insects which are not actually social like the bees in a hive, but come together all the same. Is that of the cockroach. Many species of cockroach are known to aggregate. Once the presence food is announced, they generally appear. Aggregation is the term that describes when individuals form together into a group or cluster. To use an analogy, it’s like if you were to post a “FREE BEER” sign in the center of a college campus. One student would show up and then tell his friends. Soon enough many would all start coming in droves out of the woodwork. Like the college student with the promise of free beer, cockroaches too will come together drawn towards the promise of free food.
Sometimes just one species, sometimes many different ones. You may see generations of the same ones, or they may appear all at once. Depending on the species you will see different forms of aggregation. A very strong example of this is the German Cockroach, who are well known to aggregate as well as using pheromones. Insects that use pheromones to advertise food to other individuals of their same species are generally very successful. This is even more true for the German cockroach, who is not a social insect, but when aggregate together gains many of the same benefits of those that are social. These benefits range from protection in numbers from predators; an individual is less likely to be eaten in a large group; to that of ease in finding a mate.
The last one is the real issue with German cockroaches, you don’t want them to find a mate. They can reach explosive population growth starting at very low numbers. Their ability to reproduce and mature is insanely fast even by cockroach standards and is absolutely terrifying by human standards. So having a bunch in a large group, spells disaster for any unlucky homeowner as they soon will see their home become a giant breeding ground, starting just from a handful of these little guys (and I do mean little).
Insects have a hugely beneficial service to humans, ranking in billions of dollars annually in agriculture stemming from free pollination to actual pest control of crops. This doesn’t even include the billions invested into the economy for the pest control industry itself, in urban environments. Our need for insects and our need to get rid of them is a huge and integral part of the American economy and is largely dependent on the scale of how you see them.
For instance, in the home; many insect species are indeed pests and need to be treated. On the other hand; at a larger scale; many insects have huge beneficial services they give to humanity free of charge. These include agriculture services (everything pollinates from Flies, Wasps, Butterflies, and Bees), to pest control, disease prevention, and huge advances in medicine/military technologies/computing/etc.
In fact, many military techs, computer systems, models, and medicines have been based on studying many social insects and their anatomies and biology.
Some things truly terrify me. One of them is the thought of something like one day all the spiders dying out. I know that is the dream of many Arachnophobes in the world, but the resulting nightmare in a world without spiders is much more terrifying. There is a lot of great literature and studies on the impact spiders have. For instance, the number of flies and other winged insects one spider can consume in its lifetime matched with how many spiders there are in the world (a crazy number), is far outmatched by the numbers of what they eat. You would see disease and petulance pop up in the resulting effects of the biblical numbers of flies that would appear within weeks of all Spiders disappearing.
So when you groan every time you see a spider, have to load up on Citronella candles in Spring, and buy DEET by the gallon in Summer. Know that a lot of things you enjoy come from many of the insects which may be pests at the scale of your house, but on the nationwide level are integral to how we and the economy function on many levels. The fruit you eat, the social media you use, and even some medicines, all partly came from insects in one way or another.
You should still treat your home when the need arises. While insects on a larger scale are amazing, the ones in your home in the greater scheme of things are not AS beneficial. A spider in your children’s room, ants in the pantry, and wasps in the eves; are much less appreciated.