Primary Nest or Secondary Nest: How Can You Tell the Difference?

Contents

• The primary nest: identifying the hornet’s small spring nest

• The Secondary Nest: Recognizing the Summer Fortress High Up in the Trees

• Life Cycle and Transition: How to Handle Each Type of Nest

• Conclusion

A paper ball under an awning in the spring, a large brown nest in a tree in September: these two structures may belong to the same species, the Asian hornet. The difference between them is not just a matter of size. They often correspond to two stages in the development of a colony, with the colony moving to a new location between the two.

Things to remember

• This teaching guide discusses the visual and temporal differences between the two types of nests

• This unique approach is based on explaining the phenomenon of transition (the move from elementary to middle school) to encourage active civic engagement throughout the year—a hallmark of Frelons.

• Identify the hornet's small spring egg sac

• recognize the summer fortress high up on the hill

To distinguish between a primary nest and a secondary nest, look for three clues: shape, location, and season. None of these measures is sufficient on its own. Understanding this transition from one nest to another helps avoid a common mistake: believing that the hornets have disappeared simply because their small spring nest appears to have been abandoned. At Frelons.be, vigilance is a year-round commitment, with specific precautions tailored to each season.

The primary nest: identifying the hornet’s small spring nest

Have you spotted a small beige sphere on the ceiling of your garden shed? In the spring, this discovery is worth paying attention to. The Asian hornet’s primary nest is the colony’s first structure. In the early stages, when a founding queen is still working alone, it is also referred to as embryonic nest.

The queen builds her cocoon from chewed wood fibers mixed with her saliva. The result resembles thin paper, with shades of beige or brown. Inside, the first cells house the eggs and then the larvae. The casing usually hides these cells: there’s no need to try to look inside to confirm your observation.

Here are the key signs to look for when identifying a nest in the spring:

• Size: A few centimeters at the very beginning—often around 3 to 5 cm—followed by gradual growth. A primary nest can reach about ten centimeters and sometimes even more before the birds eventually move to a new location.

• The form: a small sphere or a slightly rounded ball, wrapped in paper.

• The entrance: an opening that is generally located toward the bottom in the early stages. Its position may change as construction progresses.

• The situation: a spot sheltered from rain and wind, not necessarily very high up.

Where can you look without taking any risks? Check the undersides of roofs, awnings, carports, and garden sheds from the ground. A window frame, a shutter box, or an open outbuilding can also provide a hiding place. Do not open a suspicious box or move objects to clear away the nest: a hidden colony may react to the disturbance.

The size of the primary nest makes it impossible to count its occupants. At first, only the adult queen is responsible for construction and foraging. After the first workers emerge, several individuals—and later, depending on the colony’s growth, a few dozen—can move about within it. Therefore, seeing just one hornet does not mean there is only one hornet present.

Be careful not to confuse them. The early nests of certain wasps closely resemble those of the Asian hornet. To identify a hornet nest more reliably, observing the insects can help: the yellow-legged hornet has a very dark thorax, a mostly dark abdomen marked with a broad orange band, and yellow tips on its legs. A zoomed-in photo, taken from a distance, is better than an identification based solely on the color of the paper.

The Secondary Nest: Recognizing the Summer Fortress High Up in the Trees

Over 50 cm tall, sometimes nearly a meter by the end of the season: the secondary nest grows significantly in size. This structure accompanies the expansion of the colony, whose space requirements increase as the number of workers grows and the brood develops. It often becomes visible in the summer and is much easier to spot once the leaves fall.

The secondary nest of the Asian hornet is generally oval or pear-shaped. Its thick outer shell has distinct layers and striations in shades of grayish-brown. Unlike the small initial sphere, its entrance is often lateral. This detail is a good clue, but not conclusive proof: from the ground, the opening may be hidden by a branch or facing the opposite direction.

It is frequently found in a tree’s crown, several meters—or even several tens of meters—above the ground. The foliage can conceal what is already a large structure. Regular comings and goings around a specific spot sometimes draw attention before the nest itself does. Observing with binoculars from a distance allows you to better understand what you’re seeing without having to go under the colony.

But a nest high up is not the only possible location. A dense hedge, a bush, a building facade, or a man-made structure can also support a thriving colony. A large nest at eye level is still entirely possible, and it increases the risk of accidental contact, particularly while pruning or clearing brush.

The difference between a primary and a secondary nest is therefore based on a set of criteria:

• In the spring: A small, sheltered structure is more reminiscent of the beginnings of a colony.

• In the summer and fall: A large, often oval-shaped mass is more indicative of an advanced colony.

• A low or side entrance: It helps with identification, without replacing the observation of hornets.

• Height : It is common in secondary nests, but does not, on its own, define their nature.

The term «permanent nest» refers to the main dwelling occupied until the end of the annual cycle. It does not mean that the hornets will return there every year. The colony is annual, and the old nest is not normally reused the following year.

One final point: the size of a hornet’s nest does not indicate its current activity. A large nest discovered in winter may be empty, while a small spring nest may be home to an active queen. Before making any decisions, it is important to consider the season in which the nest was observed and to confirm the situation.

Life Cycle and Transition: How to Handle Each Type of Nest

The move doesn’t happen overnight, with the old location disappearing immediately. Relocating the nest is a transition: when the original location becomes too restrictive, worker bees begin building a new nest, while activity may continue temporarily at the original site. The colony gradually settles into its new home.

This phase often occurs in late spring or early summer, though the timing may vary depending on the weather and the colony’s development. It does not occur every year. If the original site offers enough space and favorable conditions, the nest can be expanded on site. The terms “primary” and “secondary” therefore describe a common path, not two mandatory moves scheduled on a calendar.

Here’s the key point to remember when a small nest suddenly appears to be abandoned: the colony may have failed, but it may also have moved. Do not remove this initial structure, assuming the problem is solved. Report its location, the date of your last sighting, and any hornet flight paths visible from a safe distance.

To track the life cycle of the Asian hornet in Belgium, keep these general guidelines in mind:

• In the spring: The queen bees that survived the winter emerge from their shelters and begin the nesting period. The dates depend largely on temperatures.

• From late spring through summer: The worker bees take over many tasks. The colony grows, with or without relocation.

• In late summer and fall: Established colonies produce reproductive individuals, including future colony founders.

• As winter approaches: The colony is in decline. The future fertilized queens seek shelter for the winter, usually outside the nest, while the former queen and the workers die.

What should you do if you find a hornet’s nest, whether small or large? The right answer is to avoid tampering with it. Do not swat at it with a broom, spray it with water, set it on fire, use insecticide spray, or try to block the entrance. Just because a nest is accessible doesn’t mean it’s safe.

1. Keep people and animals away. Stay several meters away—and even further if the hornets react—and block access to the area without getting close to the nest.

2. Stop any work being done nearby. Hedge trimmers, lawn mowers, and vibrations can trigger a defensive reaction when they disturb the colony.

3. Document without putting yourself at risk. Note the address, the structure, the approximate height, and whether there is any traffic coming and going. Take photos only from a safe location.

4. Have the identity confirmed. Contact Frelons.be or the appropriate reporting hotline in your area to be referred to the appropriate service.

The removal of an active hornet nest must be entrusted to a trained and properly equipped professional. Taking early action against a confirmed colony can prevent it from growing, but the removal must still be handled by a professional, even in the case of a nest in its early stages. If you are stung and experience difficulty breathing, dizziness, or swelling of the throat, call 112 immediately.

Conclusion

Keep three guidelines in mind—not a rigid rule: the small, sheltered sphere suggests spring; the large, egg-shaped nest suggests a well-established colony; and the season helps give meaning to these observations. It is the combination of these features that helps distinguish between a primary nest and a secondary nest. Neither the diameter nor the height alone is sufficient to make a definitive determination.

Your role is not to determine how many workers live inside or to inspect the entrance down to the centimeter. A useful observation consists of a few simple details: where the structure is located, when you discovered it, what shape it has, and whether insects are entering or leaving it. When shared with a qualified professional, this information makes it easier to assess the situation without putting you in danger.

A change in location warrants special attention. A spring nest that’s been abandoned doesn’t prove that the colony has disappeared from the neighborhood. Conversely, seeing hornets foraging in your yard doesn’t prove that there’s a nest on your property. Avoid following the insects through a hedge or onto a neighbor’s property: it’s better to share a precise observation than to search for a colony at all costs.

It’s important to remain vigilant year-round, but that doesn’t mean you have to treat your plants year-round. In the spring, it helps identify small nests. In the summer, it helps prevent accidental encounters during outdoor work. In the fall, falling leaves reveal nests that were previously hidden. In winter, reporting a sighting allows you to document a discovery and ask whether an inspection is necessary. An old, truly inactive nest does not warrant treatment with insecticide.

Before trimming a hedge that hasn’t been touched in a long time or using a rarely used outbuilding, take the time to observe it from the outside. This simple precaution is better than an impromptu inspection from inside the branches. If you notice a large number of large insects swarming around, stop what you’re doing and have the area checked.

Do you have any concerns about a structural issue in your home? Contact Frelons.be with a photo taken from a distance and its location. Our approach is based on this ongoing civic vigilance: identifying colonies, understanding their stage of development, and taking action at the right time—without turning a discovery into a risk.

Frequently asked questions