January: Hoverflies and Yarrow

Hoverflies (also called flowerflies or syrphidflies)

The cover photo is of a Toxomerus marginatus, or Margined Calligrapher taken by Elkins Park resident and FHSP Board member, Bennett Povlow.  It is a common species throughout North America.

Fun facts: 

  1. Hoverflies are the second most frequent pollinators to food crops after bees (1,2).
  2. The larvae of hoverflies are beneficial, eating aphids and other pests or recycling organic matter and waste.
  3. Many hoverflies look a lot like bees or wasps, but they don’t sting or bite.
  4. Hoverflies particularly like compound flowers like yarrow.

Hoverflies are fantastic pollinators in many ways.  In a 2020 study of non-bee insect pollinators, it was found that only honey bees, bumble bees, and sweat bees were more frequent visitors to agricultural crops worldwide (1). They also visit 70% of animal-pollinated wildflowers (2).  Hoverflies are able to fly great distances and have been known to carry pollen across open water for more than 100 km (about 62 miles) (1). This ability adds to the gene pool of plants that may be disconnected ecologically due to fragmentation of habitat (2). Because they can move great distances and multiply quickly, hoverflies are resilient and can adapt quickly when landscape disturbances or natural disasters occur (1).  Some species of hoverfly seem to have a color preference in flowers (2). This helps the efficiency of pollination as successful transfer of pollen will only happen if the pollinator visits flowers of the same species.

Besides pollination, Hoverflies provide natural pest control and recycling services.  Adult females of many species seek out aphid and other pest infestations and lay their eggs on the same plant.  Hoverflies can lay up to 25 eggs per day and up to thousands in a lifetime (1).  The larvae can eat up to 400 aphids, so one day of egg laying can diminish an aphid infestation by 10,000.  Other species lay eggs in ponds, streams, and culverts where their larvae feed on decaying organic matter or sewage.

Hoverflies are often mistaken for bees.  They have evolved to look like bees so that predators think they are bees and won’t prey on them. This “mimicry” is called Batesian mimicry after Henry Walter Bates, an English naturalist who discovered the phenomenon.   To identify the hoverfly, look for the antennae, which on a hoverfly are short and stubby and on a bee are long and “elbowed.”  Bees have 4 wings, and hoverflies have two.  Another distinguishing feature are the eyes.  The eyes of bees are on the side of the head, and those of hoverflies seem to take up the entire head (Holoptic, meaning having the compound eyes contiguous in front).

Want to attract these beneficial pollinators to your garden?