Environmental Science middle-school May 24, 2026

Why Are Bees Disappearing?

How pollinator decline changes ecosystems and food

A honey bee visits a flower near a farm field, showing the connection between pollinators, plants, and food crops.

Bees are declining because many pressures are happening at the same time. Pesticides, lost wildflower habitat, parasites, disease, climate stress, and poor nutrition can weaken bees and their colonies. When pollinators decline, many plants make fewer fruits and seeds, which affects ecosystems and human food.

Big Idea. NGSS MS-LS2-4 asks students to use evidence to explain how changes in ecosystems affect populations, including pollinators and the plants that depend on them.

Bees are small, but their work reaches far beyond the hive. As they move from flower to flower, they carry pollen that helps many plants make fruits and seeds. This process supports wild plants, farm crops, and many animals that eat those plants. Scientists have measured declines in some wild bee species and serious losses in managed honey bee colonies. Colony collapse disorder is one well known example. In that case, many worker bees leave a hive and do not return, even when a queen and food remain. There is not one single cause. Bees face a stack of stresses that can add up. A pesticide may not kill a bee right away, but it can make navigation harder. A landscape with fewer flowers gives bees less food. Parasites and disease spread more easily when colonies are weak. The question is about systems, not just insects.

Bees do more than make honey

A bee moves pollen between flowers while a small hive and crop field sit nearby, showing pollination as a link between insects and plants. — Pollination connects bees, flowers, and food.

A bee colony is a living system made of many individuals. Worker bees collect nectar, pollen, water, and plant resins. Nectar provides energy. Pollen provides protein and fats for growing larvae. As a bee gathers food, grains of pollen stick to its body. Some of that pollen reaches the next flower of the same species. That transfer allows many flowering plants to make seeds and fruit. Honey bees are managed by people and moved to some farms. Wild bees, such as bumble bees, sweat bees, and mason bees, also do important pollination. Different bees visit different flowers, so biodiversity matters. A field with only one kind of crop may feed bees for a short time, then become a food desert. A healthy landscape gives bees food across the season.

Pollination is an ecosystem service that depends on living relationships.

Colony collapse is a warning sign

A cutaway hive shows a queen, young bees, stored honey, and very few worker bees, illustrating colony collapse disorder. — A colony needs enough worker bees to survive.

Colony collapse disorder describes a pattern seen in some managed honey bee hives. Adult worker bees disappear from the hive, leaving behind the queen, young bees, and stored food. A colony cannot survive long without enough workers. Workers nurse young bees, cool the hive, defend it, and collect food. Researchers do not treat colony collapse as a single disease. Instead, it is a sign that several stresses may have pushed the colony past a tipping point. Parasites such as Varroa mites can weaken bees and spread viruses. Poor nutrition can make immune defenses weaker. Pesticide exposure can add more stress. Long distance transport for crop pollination can also strain colonies. The collapse of a hive is easy to notice, but the causes often build slowly.

Colony collapse is usually about combined stress, not one simple cause.

Pesticides can affect behavior

A bee flies near a crop plant while small dots show pesticide exposure through nectar and pollen, with a simple nervous system icon nearby. — Some pesticides can change how bees feed and navigate.

Neonicotinoids are a group of insecticides used on some crops, seeds, lawns, and garden plants. They act on insect nervous systems. At high enough doses, they can kill insects. At lower doses, research shows they may still affect feeding, learning, movement, and navigation in bees. That matters because a worker bee must remember flower locations and find its way back to the hive. Some chemicals can move into pollen or nectar, where bees may be exposed while feeding. Risk depends on the chemical, dose, timing, plant type, and how the pesticide is applied. Farmers use pesticides to protect crops from pests, so the issue is not simple. Integrated pest management tries to reduce harm by using monitoring, targeted treatments, and nonchemical methods when possible.

A small exposure can matter if it changes survival behavior.

Habitat loss removes food and shelter

A split landscape compares a diverse flower meadow with nesting sites to a paved and mowed area with few flowers. — Bees need food and nesting habitat.

Many bees need more than a flower patch. They need a season long supply of blooms, safe nesting places, and areas without heavy disturbance. Some wild bees nest in bare soil. Others use hollow stems or old wood. When land is paved, mowed often, or planted with only one crop, those needs can disappear. Habitat loss also breaks landscapes into small pieces. A bee may have to travel farther to find food. That costs energy and increases risk. Climate change can add another mismatch. Flowers may bloom earlier during warmer springs, while some bees may not be active yet. Restoring habitat can help. Native flowering plants, reduced mowing, hedgerows, and pesticide free nesting areas give bees more chances to feed and reproduce.

Habitat is not just scenery. It is food, shelter, and timing.

Food systems depend on pollinators

A food web diagram connects bees to flowering crops, wild plants, fruits, seeds, animals, and people. — Pollinator decline can ripple through food webs.

People often hear that one third of human food depends on pollinators. The meaning is specific. Many crops do not need bees, including wheat, rice, corn, and other wind pollinated grains. Many fruits, nuts, vegetables, and oilseed crops do benefit from animal pollination. Apples, almonds, blueberries, pumpkins, cucumbers, and many seed crops can produce more or better food when pollinators are present. That does not mean every bite would vanish without bees. It means diets would become less varied, some foods would cost more, and ecosystems would lose seed production. Pollinator decline also affects birds, mammals, and insects that eat fruits, seeds, or the plants that grow from them. A bee is one part of a larger food web.

Pollinator health is part of ecosystem health and human nutrition.

Vocabulary

Pollination: The movement of pollen from one flower part to another, which helps many plants make seeds and fruit.
Colony collapse disorder: A pattern in which many adult worker honey bees disappear from a hive, leaving the queen, young bees, and stored food behind.
Neonicotinoids: A group of insecticides that affect insect nervous systems and can expose bees through treated plants, pollen, or nectar.
Habitat loss: The removal or damage of places where organisms find food, shelter, nesting sites, and safe conditions.
Ecosystem service: A benefit people receive from nature, such as pollination, clean water, fertile soil, or flood protection.
Food web: A model that shows how energy and matter move among organisms as they eat and are eaten.

In the Classroom

Build a pollinator food web

25 minutes | Grades 6-8

Students make cards for bees, flowers, crops, birds, mammals, and people. They connect the cards with arrows, then remove one pollinator card and discuss which links change.

Schoolyard habitat survey

30 minutes | Grades 6-8

Students observe the school grounds and record flowers, bare soil, leaf litter, mowing patterns, and possible nesting sites. They use the evidence to suggest one habitat improvement for pollinators.

Stress stack model

20 minutes | Grades 6-8

Students use blocks or paper strips to model colony stress from mites, poor nutrition, pesticide exposure, and habitat loss. They compare how one stress differs from several stresses acting together.

Key Takeaways

• Bee decline has many causes, including habitat loss, parasites, disease, pesticide exposure, poor nutrition, and climate stress.
• Colony collapse disorder is a pattern seen in some honey bee hives, not a single cause.
• Neonicotinoid pesticides can affect bee nervous systems and may change feeding, learning, and navigation.
• Wild bees and honey bees both support pollination, but different bee species help different plants.
• Pollinator decline can reduce seed and fruit production, which affects ecosystems and parts of the human food supply.

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