Management of the Red Harvester Ant Pogonomyrmex Barbatus by John M
Total Page：16
File Type：pdf, Size：1020Kb
Management of the Red Harvester Ant Pogonomyrmex barbatus By John M. Davis Texas Parks and Wildlife Department Introduction This publication is designed to address 3 main questions: Figure 1: Two Harvester Ant mounds side by side. Notice the absence of plant material 1. What are harvester ants? around the mounds. 2. What is happening to them? 3. What can I do about it? sandy soil, the red harvester does not. This species 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 pesticide use as well as fire 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 animals 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 seeds 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 Arizona 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 genus 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 seed. 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 animal 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 beetles, other ants, termites, fire ant seen lined up drinking around water alates, and many other small insects 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 predation, 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 lizard. Though the rains. After a couple days of rain, the threatened Texas Horned Lizard 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 Lizards 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 frogs and toads will too.