ONH

  • 1010223
  • 4466
  • 1290611
  • 1410620
  • 1490475
  • 1530763
  • 1320456
  • 1730945
  • 1730891
  • 1730595
  • 1730773
  • 1730837
  • 1730891
  • 6600
  • 6600cu
  • 1260820
  • 4958
  • 1547
  • 1440670
  • 1010223
    1 - Thatching Ant, Formica obscuripes.

    04/28/2012 Dungeness National Wildlife Refuge, Washington

  • 4466
    2 - Thatching Ants.

    05/18/2017 Heart O' the Hills Area, Olympic National Park, Washington

  • 1290611
    3 - Thatching Ants.

    05/25/2016 Heart O' the Hills Area, Olympic National Park, Washington

  • 1410620
    4 - Thatching Ant.

    09/28/2016 Sunrise Ridge Trail, Olympic National Park, Washington

  • 1490475
    5 - Thatching Ants.

    04/01/2017 Heart O' the Hills Area, Olympic National Park, Washington

  • 1530763
    6 - Thatching Ants.

    06/05/2017 Heart O' the Hills Area, Olympic National Park, Washington

  • 1320456
    7 - Thatching Ants scavenging a Checkerspot caterpillar.

    06/26/2016 Blue Mountain/Deer Park, Olympic National Park

  • 1730945
    8 - Thatching Ant worker trimming grass.

    05/08/2018 Heart O' the Hills Area, Olympic National Park, Washington

  • 1730891
    9 - Thatching Ant male.

    05/08/2018 Heart O' the Hills Area, Olympic National Park, Washington

  • 1730595
    10 - Thatching Ant male.

    05/08/2018 Heart O' the Hills Area, Olympic National Park, Washington

  • 1730773
    11 - Thatching Ant male.

    05/08/2018 Heart O' the Hills Area, Olympic National Park, Washington

  • 1730837
    12 - Thatching Ant male.

    05/08/2018 Heart O' the Hills Area, Olympic National Park, Washington

  • 1730891
    13 - Thatching Ant male.

    05/08/2018 Heart O' the Hills Area, Olympic National Park, Washington

  • 6600
    14 - Thatching Ants tending aphids, from which they collect honeydew, carrying it back to the colony.

    06/03/2006 Dungeness National Wildlife Refuge, Washington

  • 6600cu
    14 - Thatching Ants tending aphids closeup.

    06/03/2006 Dungeness National Wildlife Refuge, Washington

  • 1260820
    14 - During the sunniest part of the day, Thatching Ants gather on side of their anthill away from the sun.

    04/29/2016 Heart O' the Hills Area, Olympic National Park, Washington

  • 4958
    15 - The act of building anthills causes plants to flourish in a ring around the hill.

    04/01/2006 Dungeness National Wildlife Refuge, Washington

  • 1547
    16 - Vegetation growing around a Thatching Ant hill.

    11/07/2014 Blue Mountain/Deer Park, Olympic National Park

  • 1440670
    17 - In the dead of winter the hill may be entirely covered in snow and frost as the temperature falls into the 20s.

    01/15/2017 Heart O' the Hills Area, Olympic National Park, Washington

  • Content Slide

Video 1 - This time-lapse video ompresses over 3 hours of a sunny morning. The sun warms the anthill, the ants swarm out, then slowly retreat to avoid the direct sun on the hill.

Among the many ant species in northern Washington State are these Thatching Ants, Formica obscuripes. They build large anthills of bits of grass and other stems. The hills can be three or more feet in diameter and reach more than a foot above ground level. They scavenge insects for food (slide 7). We’ve photographed Thatching Ants from near sea level to around 6,000 feet elevation.

We only observed the Thatching Ant males shown here on a single morning (slides 9-13).

Many ant species maintain aphid colonies on trees and other plants. Thatching ants and many close relatives particularly exhibit this behavior (slides 14 and 15). When an ant touches an aphid with its antennae, the aphid excretes a droplet of honeydew from its anus. Honeydew is a valuable source of amino acids, carbohydrates, and water. Workers collect honeydew and return to the colony to feed the brood and queen. In one intensively studied Thatching Ant colony, a single worker repeatedly returned to a particular group of aphids even after being moved many meters away. Honeydew Harvest in the Western Thatching Ant

When the sun is out, Thatching Ants congregate in a crescent-shaped area on the side of the anthill opposite to the sun (slide 14 ). The time-lapse video (video 1 24 MB) compresses over 3 hours of a sunny morning. You can see the sun warm the anthill, the ants swarm out, then slowly retreat to avoid the direct sun on the hill. (We shot the video on an iPhone X using the standard time lapse function, then retimed it in Final Cut Pro X to 50% to slow down the motion.)

In some cases, the activity of the ants causes plants to flourish in a ring around the hill. The effects on plants near ant hills may arise from several factors, including seed dispersal by the ants, a process called myrmecochory (slides 15 and 16).

Thanks to James C. Trager for the species ID on bugguide.net.