Where do ants go in the winter?

Once again, our post has been inspired by a children’s book. This time it is Bugs and Bugsicles:  Insects in the Winter by Amy S. Hansen and Robert C. Kray (illustrator). The authors follow different insects, including pavement ants, as they prepare for winter. I posted a review of this book at Wrapped In Foil and insects in winter activities at Growing With Science.bugs-and-bugsicles

When you see ants and other insects coming out in the spring, you may wonder “Where do ants spend the winter?” The answer is, it all depends on where in the world the ants live, and which of the over 12,000 species you are studying.

Where below-freezing temperatures are common, ants exhibit a number of strategies to get by.

Under the ground:

Some ants, like wood ants (Formica), can adjust the structure of their nests to help regulate the internal temperature. The huge mounds act as solar-collectors, increasing the temperature inside. When it becomes too cold, wood ants retreat to deep underground, below the frost line.

ant-mound

In wood:
Camponotus carpenter ants, live in nests in wood. Although wood is a good insulator, it still freezes inside during the winter. Carpenter ant species that live in temperate climates must have a provision for overwintering. The ants enter a state of slowed metabolism called “diapause.” Generally, the queen stops laying eggs. The workers develop large fat bodies, which can be seen as their gasters swell in size. The workers begin to aggregate more than before. In the two species I studied in upstate New York, Camponotus pennsylvanicus and Camponotus novaeboracensis, the larval stage also overwintered in the nest, but pupae and eggs did not.

Although I kept my laboratory colonies at constant temperatures and light conditions, they still periodically went into diapause. It appeared that colonies required exposure to temperatures below 15° C for about 60 days to exit diapause. Without cold temperatures, the colonies would remain in a suspended state for extended periods.

carpenter-ant1

In acorns:
Acorn ants spend the winter inside acorns on the ground. These tiny ants form small colonies. When Joan Herbers and Christine Johnson took a look at how the colonies did over winter, they found low survivorship overall. Why do the ants stick it out in acorns instead of heading underground? Some evidence suggests that by spring acorns are relatively rare, and by staying inside their prize home over winter, the acorn ants are assured of a summer home. (for acorn activities for kids, see Growing With Science).

Winter ants

One species of ant, Prenolepis imparis, has earned itself the name of winter ant because it is often out foraging in temperatures near freezing. Walter Tschinkel showed that in northern Florida these ants actually are active from November to March and then workers seal up their underground nests  and don’t come out until the following fall. Leave it to a species of ant to do things completely the opposite to most other insects.

prenolepis-imparis

Photograph of Prenolepis imparis from antweb.org (No photographer named)

No winter?

Ants that live in the tropics or hot climates don’t tend to react much to winter, although they may shut down temporarily during a dry or wet season instead. Some ants have extensive nests with elaborate ventilation systems, where the environment inside has uniform temperature and humidity year around. Now that’s the way to live.

Are ants active where you live yet?

References:

Joan M. Herbers and Christine A. Johnson. 2007. Social structure and winter survival in acorn ants. Oikos. 116(5): 829-835.

Tauber, MJ, CA Tauber and  S. Masaki. 1986. Seasonal adaptations in insects. Oxford University Press, New York.

Walter R. Tschinkel. 1987. Seasonal life history and nest architecture of a winter-active ant, Prenolepis imparis. Insectes Sociaux. 34(3): 143-164.

Filaree

heronbill

This is a filaree plant (Genus Erodium). We have a great crop in our yard this year.

heronbill1

It is sometimes called heron’s bill or stork’s bill because of its oddly shaped fruit.

heronbill2

The seed pods twist as they mature.

Apparently, the seeds are a source of food for harvester ants. We’ll see what the fire ants do.

See for example (you’ll need to scroll down):  5. Harvester Ants (Messor) & Filaree (Erodium cicutarium)

Swimming Ants

I saw some ants in the water in a lake last weekend, which led me to ask the question: Can ants swim?

Early investigators in the 1800’s did some simple studies by immersing ants in water and found that ants can survive underwater for long periods of time. Thus, ants can hold their breath, a not very exciting finding. More recent studies, however, reveal some ant species can truly swim.

Scientists in New North Queensland found a species of ant that nest in submerged mangroves. The ants hide in air pockets, but can also swim underwater. In fact, the researcher reported he wanted to film an ant, so he put it on a rock in a puddle to keep it confined until he was ready. The ant simply jumped into the water and swam away.

Another astounding example of swimming ants is the tiny ants that paddle around in the liquid inside a pitcher plant. Pitcher plants are carnivorous plants, which means they trap insects inside a jar-shaped pitcher. Once inside, the insects decompose in a pool of the plant’s digestive juices. The plant can then use the resulting ooze as fertilizer, or food, for itself.

The pitcher plant ants swim through this deadly liquid unharmed. Working together, several ants drag out some of the insects trapped inside and use them for food for their own colony. Does the plant regard this as thievery? Scientists think the ants are actually performing a service, because if too many insects fall into the pitcher the liquid can get rotten and harm the plant. In fact, the ants live in specialized hollow tendrils and drink nectar, both provided by the pitcher plant. How do these amazing ants survive the digestive fluid and climb back out of the pitcher when no other insects can?

Fire ants are known for their ability to form floating rafts of living ants, to move from place to place during floods. Here’s a video from the BBC of a fire ant raft:

Well, I guess I didn’t discover anything new. But next time I’d love to get swimming ants on video.

Did you know that some ants can swim?

Edit: (Do I need to add a “never try this at home” message?)

For more information, try:
C. M. Clarke and R. L. Kitching. Swimming Ants and Pitcher Plants: A Unique Ant-Plant Interaction from Borneo. Journal of Tropical Ecology, Vol. 11, No. 4 (Nov., 1995), pp. 589-602.

Scientists Discover Swimming Ants from ABC Online

MARK B. DuBOIS, RUDOLF JANDER Leg coordination and swimming in an ant, Camponotus americanus. Physiological Entomology, Volume 10 Issue 3, Pages 267 – 270
Published Online: 13 Mar 2008

Harvester Ant Nest Midden

During a quick hike through South Mountain Park in Phoenix, Arizona yesterday, I spotted a Messor Pogonomyrmex rugosus harvester ant mound.

messor-nest

The refuse or midden pile was covered with a fluffy material.

chaff-messor-nest

The ants apparently have been collecting the seeds of this plant, and discarding the seed coats.

creosote

It is a common plant in the Sonoran desert. Do you know what it is?

creosote-with-bee

The plant is a food source to a range of insects as well as Messor harvester ants, including more than 20 species of bees.

creosote2

It is the common creosote bush, Larrea tridentata.

The midden piles of harvester ants, as with many other types of ants, are known to improve the nutrient levels in the soil in the immediate area.

Tomorrow I will post more about Messor harvester ants.

Hum, now that I think about it, I wonder if “midden piles” is redundant, because midden is a trash heap. Anyone out there help me out on this?

Edit:  Thanks to Alex Wild for pointing out that these ants were Pogonomyrmex rugosus, not Messor.

Edit: Here’s a photo of Pogonomyrmex rugosus.

For more information, try:

Desert Harvester Ant, Messor pergandei

Dale Ward has some videos of Messor pergandei in action, as well as more information

More about cresote bush and the Zygophyllaceae (caltrop family) at the Arizona-Sonora Desert Museum