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Home , Fire ant, Harvester ant, Pogonomyrmex, Red harvester ant, Texas horned lizard

Management of the Red Harvester barbatus By John M. Davis Parks and Wildlife Department

Introduction This publication is designed to address 3 main questions: Figure 1: Two mounds side by side. Notice the absence of plant material 1. What are harvester ? around the mounds. 2. What is happening to them? 3. What can I do about it? sandy , the red harvester does not. This prefers open grassland or The following information will arid habitats and seems to especially introduce you to the fascinating world of prefer a clay loam soil. It is generally harvester ants. You will learn about said to avoid pure sand. their interesting society, foraging Red harvester ants are fairly behavior, as well as their reproductive easily identified by their large size (up to cycle. You will learn that indiscriminate a half inch) and their generally use as well as ant invasion conspicuous mound (Figure 1). These is causing their decline. Finally, you ants clear vegetation, forming a large will learn what you can do to help them circular pattern of bare ground around thrive on your property. their nest. This bare ground is often covered with small pebbles dug from What are harvester ants? within the nest itself. Extending in various directions from the main mound Harvester ants belong to the are foraging trails leading to various genera Pogonomyrmex or foraging zones. Ephebomyrmex. There are 12 species of Near the entrance to the nest is harvester ants found in Texas. Since an area called the midden. This area will Pogonomyrmex barbatus (the Red vary in diameter depending on the Harvester Ant) is the most widespread in diameter of the mound itself. The our state, it will be the one focused on in midden is the “trash dump” for the this paper. If you have access to the colony. It is where the ants deposit internet, you can learn which species pebbles, dead workers, unusable matter occur in your county by visiting from plants and brought in by http://fasims.tamu.edu/nativeexotic/. foragers, etc. Colonies 1 year old have a midden diameter of about 8 inches. Five-year-old colonies have middens The Colony about 39 inches in diameter. Below ground, the tunnels and The Mound or Nest chambers inside a mature nest (5 or Though there are harvester more years old) extend downward an species that prefer wooded areas and/or average total depth of about 6 feet. The begin new colonies. They do not first chamber encountered when an ant contribute work or offspring to the enters the nest is the sorting chamber. colony that produced them. Workers are This is where the foragers drop the sterile females. Individual workers only bounty they have gathered and head live a year. It is simply amazing that the back out for more. Extending beneath queen can pump out 10,000 workers a the sorting chamber are tunnels leading year for 15-20 years! to storage and brood chambers. Storage Within the worker class, there are chambers contain that are neatly several occupations that each will stacked and stored for consumption. perform over the period of her one-year Brood chambers contain the young life. The occupations are: nest and/or the queen. maintenance worker, midden worker, Midden forager, and patroller. Area Trunk Trail Nest maintenance workers are the youngest of all the workers. They tend to the queen and the young as well as perform routine maintenance to the nest should it need repair. These workers do not venture more than a few feet into the outside world. They move to the surface or just beneath it, sorting seeds from debris in the sorting chamber then transporting them to the lower sections of the nest. Research reveals that 75% of the individuals in the colony Figure 2: Harvester Ant mound with its trunk trails. are involved in this type of work. Toward the end of her life, the maintenance worker shifts jobs, becomes The Ants a midden worker, and joins the 25% of The average colony contains the workforce that interacts with the around 10,000 individuals. There are outside world. She then takes the three types of individuals within a “trash” that maintenance workers and colony… foragers bring into the sorting chamber 1. the queen and removes it outside to the midden. 2. “alates” or “reproductives” When a predator has reduced the (males and females that will number of foragers, or when there is a leave the colony to reproduce)… windfall of food to be gathered, midden 3. sterile female workers. workers may shift and become foragers. Workers may be foragers until A red harvester colony has only they die, or they may shift again and one queen. She is the only one to become patrollers. It is unclear what produce workers and alates. She often makes some become patrollers and lives 15-20 years. When she dies, the others not. Patrollers are the “decision colony dies. She is not replaced. Alates makers” in many cases. They decide are fertile males and females the queen where the colony is to forage each day. produces to leave the colony, mate, and This is discussed further in the next morning (between 6:00 and 7:30am) section. then head straight back to the nest leaving a chemical trail to the food. Diet and Foraging Behavior Foragers are then sent to collect the Harvesters, as the name implies, food. (Foraging peaks around 8:30am.) harvest seeds. Grass seeds in particular In general, foragers will not make up the majority of their diet. A 17- “recognize” food items unless patrollers year study of the red harvester in have “told” them it is food. Research revealed that they have a special (and personal observation) has shown affinity for Needle Grama (Bouteloua that after the foraging zones have been aristidoides). Other research has listed determined for the day, foragers will love grass, panic grass, crabgrass, ignore (sometimes even walk right over) centipede grass, buffalo grass, millet, birdseed placed very near the colony. It three-awns (grasses in the will be ignored until the next morning Aristida) and barley on their menu as when patrollers “discover” it and “tell” well. In addition to the lists researchers the foragers it is food. Then they will offer, I have personally seen them quickly gather it. bringing in grass burs and Texas Winter Foragers spend an average of 20- Grass . 30 minutes out per trip. They may travel Harvesters are known to take up to 130 or so feet from the nest to seeds from plants outside the grass forage (Figure 3). 90% of them come family like pine, ragweed, pokeweed, back with something. However, they do palmetto, nettle, evening primrose, not always return with food. They bluebonnets, and mormon tea. sometimes return with inedible bits of Though they are mostly seed “trash” that midden workers simply eaters, they will take matter as discard. It is unclear why they do this. well. This includes lice, screwworm As an aside, harvesters generally maggots, ticks, mites, snails, worms, get water they need by metabolizing fats millipedes, silverfish, spiders, grubs, in the seeds they eat, but they have been , other ants, , seen lined up drinking around water alates, and many other small puddles like cows around a stock tank. unfortunate enough to get caught. They are also known to eat feces of animals. Harvesters do not forage at night. Depending on the species, they may plug the entrance to their nest, or they may Potential not. Either way, activity ceases at night. Foraging As the sun rises, the patrollers are among Radius the first individuals to emerge. They fan 130 ft. out in various directions. Mature colonies have an average of 8 foraging “zones” they use which may extend as Harvester Ant far as 130 feet from the nest. They use Mound only 3 or 4 zones each day. The patrollers decide which ones. Patrollers locate food sources first thing in the

Figure 3: The potential foraging zone may extend about 130 ft. from the mound. Reproduction reach that age are likely to live out their The queen produces sterile 15-20 year life span. workers from the beginning to the end of the colony’s life, but when the colony What’s happening to harvester reaches 5 years of age she begins also ants? producing alates. As mentioned earlier, There are several factors that the alates do not produce offspring for have a negative impact on harvesters. the colony. Their purpose is to mate These include , competitive with other alates from other colonies and exclusion, and pesticide exposure. create new colonies. Harvesters have many natural Mating occurs from spring to fall predators. Perhaps the most well known each year, but generally follows summer is the horned . Though the rains. After a couple days of rain, the threatened Texas is alates gather at the nest entrance of each known to occasionally eat beetles, colony and seem to move in and out spiders, and flies, 65% of its diet is indecisively. On the first, clear day after harvester ants. As harvesters decline or rain, alates from all neighboring colonies are eliminated from an area, Texas simultaneously lift off and meet in one Horned are eliminated as well. location which changes from year to In addition to horned lizards, year. It is thought that the first female to other lizards will prey on harvesters. arrive at a suitable spot for mating emits Various and toads will too. a chemical signal that draws all other such as chickens, mockingbirds, plovers, alates in the area to that spot. They all flycatchers, cardinals, shrikes, blue jays, breed in a writhing mass on the ground woodpeckers, and doves all eat during that afternoon. Once a female harvesters. Invertebrates including has mated with several males, she will robber flies, wasps, assassin bugs, ant shake them off and fly to a seemingly lions, sun spiders (Solfugids), and random location. She will dig down dragonflies are also natural predators on about 18 inches and may never return to harvesters. But it is not the natural the surface. She will begin producing predators that are causing the decline in workers, and with luck she will succeed harvester populations. Natural predation at starting a new colony. is part of the life cycle and is not Starting a new colony is problematic. apparently not an easy task. However, fire ants are impacting Survivorship of mated females is less harvester ant populations by competitive than 1%. They make tasty treats for exclusion. Generally fire ants do not kill most every predator out there, hence harvesters directly. Instead, they many are eaten before they can make it efficiently harvest food within the underground. If the female survives long harvester’s foraging zone, thus enough to dig in, she still has an “uphill eventually starving the colony. road” to travel. Many new colonies are Indiscriminate use of begun in areas incapable of supporting insecticides, however, has also taken a them. Consequently, they starve. heavy toll on harvester populations. However, since survivorship for colonies Many people have waged war directly two years or older is 95%, ones that on harvester ant colonies not realizing how fascinating and valuable they are. I believe that many people would not have so that it is suitable for harvesters, and poisoned colonies had they known how check for colony establishment each fall. critical harvesters are to the survival of There is a combination of two horned lizards. basic strategies that you can employ to Today, I believe that most people help harvester ants. First, you can no longer intend to harm harvesters. manage and enhance the habitat to However, they inadvertently do so by provide optimal foraging for your broadcasting insecticides intended to kill colonies. Second, you can help keep fire fire ants. ants from destroying the colonies you Controlling fire ants is are encouraging. important. Unfortunately, some professionals are recommending Habitat Management and Enhancement broadcasting bait products over large You now know that harvester areas. This kills fire ants, but ants are seed eaters, preferring grass unfortunately it kills native ants seeds most of all. You also know that a (including harvesters) as well. Once mature colony will forage up to 130 feet native ants are eliminated from an area, from the mound. Using this information, it becomes even easier for fire ants to I recommend planting locally native invade again. Ways to address this grasses within the forage radius. Check problem are discussed in the following with your local Texas Parks and Wildlife section. biologist to determine which grasses are native to your county. What can I do to help harvester During the winter many of our ants? native grasses can be divided and Though difficult, it is possible to transplanted from wild stock should you transplant or reintroduce harvester ants be fortunate enough to have the desired to a property where they no longer exist. species growing on your property. If By using an extremely large tree spade this is the case, you may simply dig a and removing the entire colony during portion of the plant (making sure to get the night when they are inside, some plenty of root mass along with it) and people have been successful at moving transplant it into the forage radius of mounds. However, if harvesters were your harvester ant mound(s). Be sure to once present and are no longer, there is a water the transplants well. A thick layer reason. Reintroducing them without of mulch around the transplants will help solving the initial problem that them as well. If possible, watering the eliminated them in the first place may area once a week during the following only cause the newly transplanted summer will greatly increase survival of colony to suffer the same fate of those the transplants, but many may survive before them. Therefore, should you with adequate rainfall alone. have existing colonies, treasure them! Should you choose to sow seeds Since mating occurs in a mass of of desirable species, I recommend you chaos, it is next to impossible to track use the “seedball” method. Harvesters particular alates and, therefore, are seed eaters, so they are likely to determine how far they disperse to start harvest any seed you scatter within their a new colony. If you do not have forage zones. To help decrease the existing colonies, manage your property chance of that happening, create seedballs. Mix (dry) commercially harvesters can access the seeds by the available red pottery clay, compost, and holes punched in the container (Figure seeds (using a ratio of 5 parts clay, to 3 5). This should create a feeder that parts compost, to 1 part seeds). While reduces the chance of birds, rodents, or still mixing, moisten the ingredients to other seed eaters getting the food. the consistency of a thick paste. Roll the To take full advantage of the paste-like mixture into marble sized harvester’s behavior, remember to feed balls. This will encase much of the seed colonies at sunrise so that the food is out in the clay, protecting it from harvesters, the shortest amount of time before the birds, rodents, etc. The compost in the patrollers find it. mix will serve to nourish germinating seeds. As rainfall melts the clay, the seed has all it needs to sprout and grow. Though I believe it is best to plant the plants that the harvesters will feed on, you may also choose to feed your colonies directly. Before beginning a feeding program, you must first eliminate or greatly reduce the fire ant population within the foraging zones of your harvester mounds. Otherwise you will only be feeding fire ants. Ways to accomplish this are discussed later. Once you have gotten fire ants under control, you may begin to feed your harvesters. There are several ways to do this. At sunrise, simply pile native seed, crushed peanut hearts, oat flakes, or other similar food items near the mound and watch them haul it to the Figure 4: You can make a feeding station by nest. Or you can create feeders that punching 3/16” holes into a coffee can just better ensure harvesters get the food. beneath the rim of the lid. Either way you choose, be careful to avoid generic birdseed mixes as these may contain seeds of exotic plants that can become a problem on your property. To make a feeder, simply punch a series of 3/16” holes (on 1” centers) in a container (such as a coffee can) just below the top rim (Figure 4). Driving a 16 penny nail through the can will be about the easiest way to do this. Fill the container with the food you are offering. Secure the lid. Place the container upside down near the mound. Doing this Figure 5: As you turn the feeder over, the will allow the seed to fall such that seeds will become available to the harvesters through the holes you created. Fire Ant Management baits. Always follow instructions on the I have had good luck using label. beneficial nematodes (microscopic Fire ants tend to aggressively worm-like creatures) to control fire ants. defend a food source. If only enough bait However, we do not know how these to treat an individual mound is used, fire nematodes affect harvesters. Until we ants will defend the bait as a food source know they will not harm harvesters, I and should not allow other ants to get to cannot recommend them. it. Do not over treat a mound as this may To control fire ants while allow other ant species to be killed. Do protecting harvesters, treat fire ant not place bait material directly on the mounds individually with organic mound as fire ants do not typically methods or bait products. Do NOT forage on top of the mound. Place the broadcast poisons or baits as bait around the mound so that it will be recommended in some fire ant control treated as food and collected. programs. To treat fire ant mounds within Individual fire ant mounds harvester forage zones, use the organic outside a harvester forage zone (130ft. methods as described earlier but follow radius from a colony) may be treated at up with a more time-restricted use of a various times of the day depending on bait product containing spinosad. the product used. Organic contact Spinosad is a mild stomach toxin that killers, such as compost and citrus oil kills fire ants, but doesn’t affect sprays, drenches, etc. may be home harvesters. Products containing made or found in local organic nurseries spinosad include Justice and Eliminator. and are quite effective at killing fire ant Recall that harvesters don't workers. Contact local organic nurseries forage at night. Fire ants do. Therefore, for these products or visit the website to further reduce the chance of harming www.dirtdoctor.com to learn how to harvesters, place fire ant bait material make your own. around individual fire ant mounds within Though these methods work well harvester forage zones during the on workers, it is difficult to be certain evening. Use just enough for the workers you kill the queen with them. Killing to haul it underground before sunrise the her may require a bait product that the next morning. workers feed her. When treating fire ant mounds For fire ant mounds outside a that are extremely close to harvester harvester forage zone, first use the mounds or simply as an extra precaution, organic methods to knock the colony bait stations may be beneficial. To back, then use a fire ant bait product create bait stations, drill holes into the containing fenoxycarb a few days later lids of small containers such as film to get the queen(s). Fenoxycarb is an canisters (Figure 6). The holes should growth regulator with low toxicity be 1/16” to allow fire ants to enter while to birds and mammals. It works by excluding all other larger species. Place interfering with the metamorphosis from the bait product in the containers, secure larva to adult. The colony will run out the lids and place the containers on their of workers. The queen will starve. side near an active fire ant mound. This Products containing fenoxycarb include allows fire ants to get the bait while Award, Logic, and Hi-Yield fire ant excluding harvesters. More than one station per mound may be required depending on the size of the mound.

Conclusions Harvester ants are fascinating and highly beneficial insects. They are crucial to the survival of the . Though there are pockets in our state where harvester ants are plentiful, overall they are facing a difficult challenge to their survival. The actively out- competes the harvesters for food. As a result, harvesters are declining in areas where fire ants are abundant. Figure 6: Bait stations can be created by drilling th To help harvester ants thrive, fire 1/16 inch holes in the lids of small containers. ant populations must first be reduced to minimal levels. Once this is accomplished, then an active management strategy to benefit harvesters directly can be implemented. Harvesters are seed eaters, specifically preferring grass seed. By planting native grasses within the forage zones of harvester ant mounds landowners can provide long term food supplies. A more immediate, albeit labor intensive, approach is to feed harvester colonies directly using feeding stations. There are many things that can be done to help harvester ant populations to increase. If you have harvester ants on your property, appreciate them and do what you can to ensure the continued Harvester ants working diligently to harvest seed survival of this fascinating member of from a coffee-can feeder. our native ecosystems.

References Hook, Allan W. and Sanford D. Porter, 1990. Destruction of Harvester Ant Colonies by Invading Fire Ants in South-Central Texas, Southwestern Naturalist, Vol 35, pp. 477-478.

Cohen, Allen C., and Jacqueline L. Cohen, 1990. Ingestion of Blister Beetles by a Texas Horned Lizard, Southwestern Naturalist, Vol 35, p369.

Pianka, Eric R., and William S. Parker, 1975. Ecology of Horned Lizards: A Review with Special Reference to Phrynosoma platyrhinos, Copeia, No. 1, February, pp. 141-162

Taber, Stephen Welton, 1998. The World of Harvester Ants, Texas A&M University Press, College Station.

Gordon, Deborah M., 1990. Ants at Work: How an Insect Society is Organized, The Free Press, New York.

Moody, J. V., and O. F. Francke, 1982. Subfamily . Pt. 1 of The Ants (: Formicidae) of Western Texas, Texas Tech University Graduate Studies, no. 27. Lubbock: Texas Tech Press.