Beneficial Insect Spotlight: Paper Wasp

Right outside our back door, we have a small herb garden.  Last fall, we planted three parsley plants at the back of the herb garden.  This spring, they grew considerably at first and then immediately started flowering and haven’t stopped now for several weeks.   Because the herb garden is so close to our back patio door, we often stand at the door and watch a variety of insects that stop to enjoy the parsley flower nectar.   This plant really attracts an assortment of flies (houseflies, tachinid flies, hoverflies), wasps (paper wasps and thread-waists), and bees (honeybees, sweat bees, mason bees and solitary bees)!  Many of these insects prefer the shallow nectaries of flower umbrels as opposed to other species of flowers with deep nectaries which require elongated mouthparts.

umbrels of parsley flowers

My wife, who is understandably a little alarmed by the number of bees and wasps by our back door (she’s allergic to their stings), asked me why we want so many wasps in the garden.  She understands that parsley is the host plant for Eastern Black Swallowtail caterpillars and can appreciate the beauty that adult butterflies bring to the garden, but wasps are an entirely different story in her book.  I explained to her that wasps are beneficial insects to gardeners.  She then asked me, “In what way are they beneficial?”  To her, they seem like a pest to avoid and not one to invite so freely into the garden.

The fact of the matter is that wasps are beneficial insects in the garden for two main reasons.  The first is that they are pollinators.  I find wasps on a number of flowering plants in the garden, including squash, cucumber, zucchini and melons.  This family of plants, called cucurbits, have unisexual flowers, meaning that each flower either contains anthers or ovaries (i.e. is male or female), but not both.  They cannot self-pollinate.  Pollinators such as butterflies, bees and wasps are drawn to the flowers of these plants by color and are enticed to stay by the nectar that the flowers offer.   As they lap up the sweet goodness, the flower’s pollen sticks to the legs and bodies of the pollinator, which then flies to another flower and deposits some of this pollen there.  With regards to cucurbits, the male and female flowers need pollen from one another in order to produce fruit.  Pollinators are the key to making this happen as they move from male flower to female flower, depositing pollen.

Wasps are beneficial in another way.  They are parasitic.  They feed on a number of garden pests, including flies, beetle larvae and even caterpillars.  To me, this is where wasps fall into a sort of gray area when you are butterfly gardening.  Naturally, a butterfly gardener wants to raise butterfly larvae to adulthood, but other creatures in the garden see butterfly larvae as a good meal.  So, there’s a catch-22 here.  A butterfly gardener grows plants that attract beneficial insects, and some of those beneficial insects end up killing one another.  Wasps do their part, however, since out-of-control caterpillar populations can decimate plants and crops.  Still, I cringe at the thought of my little caterpillars preyed upon by wasps and even birds.  It is nature, however, and everything exists in balance, so I have to let the natural process play out.  All things considered, wasps are beneficial to my garden – I just wish they preyed exclusively on beetle larvae!

The Paper Wasp

If you’ve ever seen a wasp nest in the shape of an umbrella hanging from a thin thread under the eaves of a house, then you’ve seen how paper wasps live and how they got their name.  Paper wasps gather fibers from plants, chewing and mixing them with saliva to form a substance similar to paper, which is then formed into nests with many adjoining hexagonal cells.

Nests are started by a single queen in the spring, which can grow to hold up to two hundred cells.  The queen overwinters in brush or wood piles and emerges in the spring to expand her kingdom.  After picking a suitable spot for a nest, she works tirelessly, gathering and chewing plant fibers and forming the first several cells.   In these cells, the queen lays her eggs, which hatch into worker (non-queen females) and male larvae.  As the brood grows, the queen continues to do most of the egg-laying and studies show that her behavior actually suppresses the ovarian functions in subsequent female wasps so that she remains the dominant female.  Workers care for the queen’s larvae and continue to build the nest, while also visiting the field to harvest nectar, plant fibers and insects for larval food.

Adult wasps do not eat insects, they subsist entirely upon nectar.  Workers collect caterpillars and carry them back to their nests, first stinging them to paralyze them.  Then they stuff the paralyzed caterpillar into one of the prepared cells, and the queen deposits a single egg on the caterpillar’s body.  The egg hatches and a tiny wasp larva emerges and finds all the food it could possibly need until it pupates and emerges as an adult, winged wasp.

Males are needed only for fertilization of the queen.  The queen has a specialized organ called the spermatheca, which captures and holds the male wasp’s sperm for later fertilization of eggs.  Males typically live short lives.  Late in the season, they mate with female offspring of the queen, which then leave the colony to overwinter and emerge in spring to start their own colony.  All other members of the colony, including the original queen, perish during the winter.  The newly mated female holds the sperm in her spermatheca until the following spring when she begins laying eggs on harvested caterpillars!

As far as hierarchy in the colony goes, the founding queen is generally the dominant queen, and rules over her workers to ensure their cooperation and subservience.  The most aggressive females will take up the role of queen should the founding queen die, and on rare occasions, aggressive females can root out the founding queen in a process called usurpation.  The aggressive female then takes over as queen, while the founding queen takes on the role of worker.  Despite this aggressiveness, paper wasps are not aggressive except in defense of their nests.  As I tell my wife, they won’t even bother you should you sit right next to the parsley flowers to watch them.  They are more interested in feeding than they are in you!

The photos below are of a red paper wasp (Polistes carolina) on parsley flowers.  This wasp is common from as far west as the Texas panhandle to the east coast up through New York.  They are quite large at an inch in length.

(Click on any photo to view larger)