Insects do poop, but we call their poop "frass." Some insect frass is liquid, while other insects form their frass into pellets. In any case, the insect is eliminating waste from its body through its anus, which meets the definition of poop, for sure.
Some insects don't let their waste go to waste. The insect world is filled with examples of bugs that use their frass for food, for self-defense, or even for construction material.
Insects That Put Their Poop to Good Use
Termites aren't born with the gut microbes needed to digest wood, so they first feed on feces from adults, often right from their anuses. Along with the frass, the young ingest some microbes, which then set up shop in their guts. This practice, called "anal trophallaxis," is also practiced by some ants.
Bess beetles, which also feed on wood, don't have larval jaws strong enough to handle the tough fiber. They feed on the protein-rich poop of their adult caretakers instead. Bess beetles also use poop to construct protective pupal cases. The larvae can't do the work on their own, though. Adults help them form the feces into a case around them.
Three-lined potato beetles use their poop as an unusual defense against predators. When feeding on nightshade plants, the beetles ingest alkaloids, which are toxic to animal predators. The toxins get excreted in their frass. As the beetles' poop, they contract muscles to direct the flow of feces onto their backs. Soon, the beetles are piled high with poop, an effective chemical shield against predators.
How Social Insects Keep the Poop From Piling Up
Social insects need to keep a sanitary household, and they employ clever housekeeping strategies to remove or contain all that frass.
Frass cleanup is usually a job for adult insects. Adult cockroaches gather up all the poop and carry it out of the nest. Some wood-boring beetle adults pack frass into older, unused tunnels. In some leafcutter ant colonies, specific ants get the poop removal job and spend their entire lives carting off their family's frass. Being the designated pooper scooper is a thankless job, and relegates these individuals to the bottom of the social ladder.
Social bees can hold their poop in for weeks or months at a time. Bee larvae have a blind gut, separate from the alimentary canal. The poop simply accumulates in the blind gut through their development. When they become adults, the young bees expel all the accumulated waste in one giant fecal pellet, called the meconium. Honey bees ceremoniously drop their mighty larval turds on their first flights from the nest.
Termite guts contain specialized bacteria that sanitize their feces. Their poop is so clean they can use it as construction material when building their nests.
Eastern tent caterpillars live together in silken tents, which quickly fill with frass. They expand their tents as they grow and the poop accumulates, to keep some distance between them and their frass.
Insect Poop in the Ecosystem
Frass makes the world go 'round, in some important ways. Insects take the world's waste, digest it, and poop out something useful.
Scientists discovered a link between the rainforest canopy and the forest floor. It was insect poop. Millions of insects inhabit the treetops, munching away on leaves and other plant parts. All those insects also poop, covering the ground below with their frass. Microbes go to work decomposing the frass, releasing nutrients back into the soil. Trees and other plants need the nutrient-rich soil to thrive.
Some insects, like termites and dung beetles, serve as primary decomposers in their ecosystems. Termite digestive systems are chock full of microbes capable of breaking down stubborn cellulose and lignin from wood. Termites and other wood-eating insects do the hard part, then pass the significantly decomposed plant bits on to secondary decomposers through their frass. An enormous percentage of forest biomass passes through insect guts, on its way to becoming new soil.
And how about rotting carcasses and animal dung? Insects help break down all the nasty bits in the environment and turn them into something much less objectionable, frass.
Most insect poop isn't large enough to contain whole seeds, but poop from big grasshoppers called "wetas" is an exception to that rule. Scientists found the wetas, which live in New Zealand, can poop viable fruit seeds. The seeds found in weta frass germinate better than seeds which simply fall to the ground. Since the wetas move, they carry the fruit seeds to new locations, helping trees spread throughout the ecosystem.