Each insect species plays one or more roles in the food web: prey, predator, parasite, or parasitoid. The need to feed connects them to one another, and to the rest of the living world. Let’s explore how this interconnection helps maintain the balance of ecosystems and biodiversity.
Prey insects: an essential food source
Most insects sit at the base of the food web. By feeding on plants (primary producers that can make their own food), they become a vital source of protein and energy for the animals that eat them.
Many animals depend on insects and consume them in large quantities, whether in their immature stages or as adults. For example, mayfly nymphs help feed aquatic insects, frogs, and fish. Once they become adults, mayflies provide an abundant food source for dragonflies, birds, and other insect-eating animals.
Humans, too, eat insects in many parts of the world. In several cultures, particularly in Mexico and Thailand, protein-rich insects are part of the diet.
Predatory insects: nature’s regulators
Predatory insects play an essential role in regulating ecosystems. By hunting, killing, and eating their prey, they help keep certain species from multiplying too quickly and contribute to a healthy natural balance. This control is crucial for preventing outbreaks of insects, or other animals, that could disrupt the ecosystem.
Without predatory insects, crops and wild plants could be threatened by surging populations of pest species. They also help reduce problems such as the spread of diseases and intense competition for food among species.
Some examples of insect predators include:
- Lady beetles, which feed largely on aphids
- Mantids, which capture a wide range of insects using their raptorial forelegs
- Dragonflies, which hunt mosquitoes, flies, and other insects in flight
Parasitic insects: living at the expense of others
Parasitic insects draw the nutrients they need to survive by living on the surface of, or inside, another organism, called a host. This behaviour can harm the host and sometimes make it sick.
In the insect world, there are many kinds of parasites. Some live on the skin of mammals, like fleas; others attack plants, like aphids; and there are many others.
Parasitoid insects: developing inside another organism
Finally, parasitoid insects need a host in order to develop. In most cases, the female lays an egg inside or on the host, and the larva grows there over time.
At first, the host may appear unharmed. But once the larva begins to feed, often while the host is still alive, the effects become noticeable. In some cases, the host is paralyzed before the egg is laid and is slowly consumed by the growing parasitoid.
After a while, the host dies and one or more adult parasitoids emerge. These new creatures are then ready to mate and start the cycle again.
Several parasitoid insects are used in biological control. For example, tiny wasps lay their eggs inside the eggs of moths and butterflies whose caterpillars damage crops, while other species target aphids. This is a good reminder that insects can also play the role of host.
In larger species, the behaviour can be especially striking. For instance, a wasp in the genus Pepsis lays a single egg inside a large tarantula it has first paralyzed.