If you’ve spotted a strange brown, foam-like lump attached to a fence post, branch, or shrub, don’t be too quick to remove it. It’s most likely a praying mantis egg case, known as an ootheca. While it may resemble a wasp nest or fungus at first glance, this protective casing can contain hundreds of developing mantis eggs. Built to withstand rain, cold weather, and predators, it’s an important part of the insect’s life cycle.

Praying mantises are highly valued by many gardeners because they’re natural predators that feed on pests such as aphids, flies, and caterpillars. During the colder months, the eggs remain safely protected inside the ootheca. Once spring arrives and temperatures rise, dozens—or even hundreds—of tiny mantises emerge, ready to hunt insects almost immediately and help keep garden pests under control.

If the egg case is in a location where it might be damaged, it can be moved carefully by cutting the small branch or surface it’s attached to and placing it upright in a sheltered area, such as a shrub. Otherwise, it’s best to leave it undisturbed. Removing the ootheca means preventing an entire generation of beneficial insects from hatching.

A praying mantis egg case is firm, ridged, and foam-like, making it easy to confuse with other objects. Unlike papery wasp nests or soft, moist fungi, an ootheca has a tough outer shell designed to protect the developing eggs. What may seem like an odd backyard discovery is actually a fascinating glimpse into nature—and one that could benefit your garden for months to come.