A Wandering Botanist: Pollinators and Flower Visitors

All sorts of small animals can be found on flowers. All of them can safely be called flower visitors. Of the flower visitors, some are pollinators. What is the difference?

Pollinators do a service for the plant, pollinating; flower visitors do not.

Review of Pollination. Skip if it makes your eyes glaze over: Pollination is plant reproduction; pollen is transferred from where it is produced (anthers) to the female part of the flower (stigma/style/ovary). It lands on the stigma and grows down the style into the ovary. In the ovary, sperm combines with an egg, to produce the embryo which will develop into a seed.

Plant reproductive parts in a simple flower

But plants are immobile. A few plants have anthers that wilt and fall onto the stigma (taller than in my sketch above). This, however, can only produce self-pollination, since genes of the parent plant are in both sperm and egg. Crossing between different plants (called outcrossing) provides different genes from each parent, potentially produceing better-adapted offspring since they are more diverse. (Notice that humans build-in outcrossing since we have sperm and eggs in two different people).

Some plants are wind- or water- pollinated, using wind or water to carry pollen to another plant. However, most flowering plants are pollinated by animals, collectively called pollinators. Pollinators are helpful for slopping pollen between the tiny flowers of a sunflower or a carrot, but they are crucial for moving pollen between two penstemon plants or two apple trees.

Back to flower visitors and pollinators. The distinction between flower visitors and pollinators is that pollinators carry pollen and drop it off on the stigma of a plant of the same species. Flower visitors do not. Spiders, for example, are flower visitors, not pollinators, because they sit waiting for prey on one flower. They may be dusted with pollen, but they are unlikely to carry it to another flower.

spider in morning glory flower

Animal pollination is complicated. The pollen must be attached to an animal which subsequently leaves the pollen on a stigma of a flower of the same species, ideally on a different plant. Nectar inside the flower and the pollen itself are incentives for animals to feed in flowers. Famous pollinators like honey bees, bumblebees, and hummingbirds visit dozens to hundreds flowers in a day, moving pollen every time. Plants have adapted to facilitate pollination in many different ways, creating the variety of flowers we see.

Monarda attracts hummingbirds because the flowers are red, a color the birds are attracted to, stick way up in the air so they are easy to reach for a small flying bird, with lots of nectar in the throat of the flower. The pollen and stigma are along the top of the mouth of the flower, easily bumped into by the hummingbird's head

The line between flower visitor and pollinator varies. A fly would be a flower visitor if, dotted with pollen, it went from the flower to a rotting fruit and never returned, but it would be a pollinator if it visited several sunflower heads, moving pollen with each visit.

From the plant's point of view, a good pollinator picks up lots of pollen while on one flower and goes directly to a flower of the same species on a different plant, where the pollen is deposited on the stigma. Lots of sloppier pollination works too, for example beetles pushing pollen from one aster floret to another.

Bees, whether honey bees, bumblebees, or solitary bees, are good pollinators because they visit a lot of flowers and often specialize, going only to one species of flower at a time. Some bees collect pollen but lose a few grains to pollination on the next flower; plants over-produce pollen to allow for pollen-gathering. Other bees are fuzzy, with hairs on which pollen gets caught, to brush off on the stigma of the next flower.

Hummingbirds are excellent pollinators because they will fly long distances to find another flower they like, with pollen from the first flower stuck to the feathers on their faces.

Butterflies and moths are mostly not very focused on any one plant species, but they feed on nectar and brush pollen on themselves in the process, so can be effective pollinators.

Wasps are considered less effective pollinators than bees because they have smooth bodies to which pollen doesn't adhere easily.

House flies and beetles are not particularly good pollinators because, although they walk around the flower feeding, they are likely to go next to a flower of another species or sit on a leaf, where the pollen is wasted.

Ants can be common flower visitors, but are very poor pollinators because they cannot fly so the same ant does not visit very many flowers. Furthermore ants clean themselves and other ants, removing pollen.

Spiders, ambush bugs, and dragon flies are predators that visit flowers to prey on insects found there; they rarely move between flowers carrying pollen.

In all the above, there are exceptions to my generalizatons. Look carefully.

Determining if an animal is a pollinator not a flower visitor requires careful study. Not only are many flower visitors small, there is an "uncertainty principle" because you cannot both catch the animal to see what pollen it has and watch that animal's undisturbed behavior. Obviously there are methods, like capturing some and watching or filming many others, but it requires substantial effort. Another important point about ecological studies of pollination is that the season progresses; the same study a week later may give different results because flowering has passed its peak or another plant has come into bloom, changing the options of potential pollinators. Meanwhile flower visitors may stop visiting flowers to lay eggs or a predator species may have grown big enough eat flower visitors and so now lurks on the flowers, which changes prey behavior. And more. It is wonderful stuff but hard enough that even in 2025 we have more questions than answers.

ambush bug on sunflower

What are the flower visitors if they aren't pollinators?

Some are individuals that can pollinate but don't, because they don't actually carry pollen to another flower of the same species. These must be numerous, but generally are thought of as pollinators if their species pollinates well.

But beyond that, non-pollinating flower visitors include:

Predators, particularly ones that prey on pollinators. For example, there are wonderful flower-colored spiders, camouflaged against yellow or orange. Visits of pollinators to flowers are predictable, so flowers predictably attract predators.

Seed-predators. Flowers develop into fruits, full of seeds that are good food for insect larvae. Moths and flies for example, lay their eggs in the developing seeds and their larvae will consume the seed. This is "seed predation" but by moving around the flowers, some seed predators pollinate. In fact, some seed predator species, such as the yucca-moth and moth seed predators of tropical cycads, have evolved to be the main or only pollinator of the plant.

Flies on flower heads: are they pollinators?

Mating. Flowers are great places for finding a mate. Bees, flies, moths and others go to flowers to find a member of the opposite sex to mate with there. Probably both sexes fed there; that was how it became the meeting place. These are tricky, since feeding on nectar or pollen, and moving around, they likely pollinate, even though finding a matewas the animal's main attraction to the flower.

Keeping Warm. In cold climates insects hang out in flowers to warm up, the light color of the flower and the disc shape warming it faster than the air. Probably some of these insects pollinate, but not if they stay in one flower are keeping warm.

Fly in flower; top of the Rocky Mountains, 11,800 ft. elevation

Flowers and pollinators evolved together over the last 125-130 million years. Pollination is mostly a mutualistic interaction, plants reproducing, animals feeding. But of course, having produced the food resources for pollinators, lots of other animals moved in to use those resources. A lot of the complexity of plant flower structure helps keep freeloading flower visitors away from the nectar and pollen while giving legitimate pollinators access.

Flower visitors make watching the animals on flowers all the more diverse and interesting.