Trichogramma wasps are nearly microscopic, non-stinging wasps that very effectively prevent damaging infestations of many types of caterpillars. These include pecan case bearers, webworms, and tent caterpillars, among others. They are completely harmless to people and animals and have little effect on butterfly populations. These wasps lay their eggs inside the eggs of the caterpillars, and their larvae then destroy the caterpillar eggs as the young wasps grow.
To be most effective, the timing of the release of the wasps is critical. When the wasps are purchased they are actually sold as moth eggs containing the wasp larvae. The eggs are sold on small tabs that resemble sand paper. To release the wasps, simply pin one or two squares as high as possible to the shady side of the trunks of trees where control is desired. To be most effective, trichogramma wasps must be released at specific times of the year while the caterpillars are in the egg stage.