Wasps, which belong to the same insect order Hymenoptera as bees, are often perceived solely as predatory insects, overlooking their significant contribution to plant reproduction. While bees are recognized as the most prolific pollinators, wasps do engage with flowering plants and facilitate the transfer of pollen. Their role is largely misunderstood because their primary foraging behavior is not focused on pollen collection. However, an adult wasp’s need for high-energy sustenance, particularly nectar, drives them to flowers, making them accidental but effective couriers of genetic material for countless plant species.
How Wasps Pollinate
Wasp pollination occurs as an incidental byproduct of their search for nectar, the high-energy fuel adult wasps require for flying and hunting. Unlike bees, which deliberately collect pollen to feed their larvae, most wasps are carnivorous, provisioning their young with paralyzed insects or spiders. Wasps largely lack the specialized, branched hairs (scopa) that allow bees to efficiently gather and transport pollen grains.
Pollen transfer by wasps is typically an opportunistic process. When a wasp lands on a flower to drink nectar, pollen grains stick to its relatively smooth body, mouthparts, and legs due to physical contact. As the wasp moves to another flower, it brushes off this inadvertently collected pollen, facilitating fertilization. This method makes the average wasp a less efficient pollinator than a bee, but their activity is sufficient for the reproduction of some plants, such as milkweed or figwort.
Some exceptions exist, such as the Masarinae subfamily, known as pollen wasps. These wasps collect pollen in their crop—an expanded portion of the digestive tract—to provision their nests, making them highly effective pollinators for specific plants like beardtongues (Penstemon).
Diverse Roles in the Wasp Family
The diversity within the wasp family, which includes tens of thousands of species, explains the wide range of their interactions with flowers. The groups most commonly observed visiting flowers for nectar are the social wasps, such as yellow jackets and paper wasps, and many solitary wasps, including potter wasps. Adult social wasps require sugar to power their colonies and sustain foraging activities, even though their larvae are fed meat.
Solitary wasps, which do not form colonies, also rely on flower nectar to fuel their hunting expeditions. These wasps, such as predatory spider wasps or mud daubers, use their sting to paralyze prey for their offspring but must replenish their own energy reserves through sugary liquids. This widespread nectar-feeding habit means that a large number of wasp species are generalist pollinators for a variety of plants, particularly those with easily accessible nectar like plants in the carrot family (Apiaceae) and the daisy family (Asteraceae).
Obligate Pollination: Specialized Relationships
The most profound examples of wasp pollination involve co-evolutionary, obligate relationships where a specific plant cannot reproduce without a specific wasp species. The most recognized example is the specialized mutualism between fig wasps and the nearly 1,000 species of Ficus trees globally. Each fig species is typically pollinated by only one corresponding species of minute fig wasp from the family Agaonidae.
The fig is a closed flower cluster called a syconium, accessed only through a tiny opening called the ostiole. The female fig wasp, attracted by chemical cues, enters the syconium, often losing her wings and antennae. Once inside, she deposits eggs into short-styled flowers, which develop into galls for her offspring. She simultaneously transfers pollen carried from her birth fig to the long-styled flowers, enabling seed production.
Male fig wasps, which are often wingless, hatch first and mate with the females while they are still in their galls. They then chew an escape tunnel for the newly impregnated females before dying inside the fig. The females exit the syconium covered in pollen and fly off in search of a new fig in which to lay their eggs, perpetuating the cycle for both the wasp and the fig tree.