Although the mounds of fire ants are the most visible part of their home, this structure is used only for regulating the temperature of ants and brood during certain seasons and parts of the day. A large portion of the nest is hidden from view underground. The subterranean nesting habits of ant colonies can make the transition from field to lab studies tricky– how does one go about separating thousand and thousands of ants and their delicate brood from a heap of dirt?
In fire ants, the drip floatation method takes advantage of a flood-survival adaptation of the ants to accomplish this task (Banks et al, 1981).
The first step is, of course, to obtain field colonies. This is best done early in the morning, when the queens and brood are likely to be high in the nest, warming up from the cold night. I also recommend gloves, long pants, and boots. Fire ant colonies can be dug up from the field and stored in a container lined with baby powder, which will prevent the ants from climbing the sides and escaping. Colonies should be allowed to settle into the container for at least 24 hours. This allows the ants time to locate brood and re-establish tunnels to the surface.
Water is then slowly dripped into the container, drop by drop. Again, this process should be slow enough to allow the ants time to rescue brood and move to the surface. I find this takes somewhere between 4-8 hours depending on the amount of dirt and the size of the container.
In our lab we have a PVC pipe arrangement allowing multiple colonies to be dripped at once, but this set up could be as simple as a bucket under a slowly dripping faucet, or hose.
The water should drip straight down into the center of the bucket, to avoid washing away the baby powder. (Keep an eye out for splashing!)
As the water fills the bucket, the worker ants swarm to the surface, carrying brood and chivvying along queens and alates. These swarming ants will quickly explore every avenue for escape, so make sure surfaces are too slick with baby powder to climb, and any grass stems and debris have previously been removed.
Large numbers of fire ants can make quite a pile, and each damp fire ant can wash a little of the baby powder away. The fire ants should be checked on frequently, and more baby powder added as needed, or you may enter the room to find a mostly empty bucket, and a swarm of agitated escaped fire ants roaming your floor!
As the water level rises, and the worker ants will form a living raft with their bodies, sacrificing the ants on the bottom to save the workers, brood, queens and alates which pile on top.
This behavior allows fire ants in the wild to survive flooded conditions, floating to safety on a raft of their drowning nestmates. When they strike land (or another dry surface) the ants swarm out and seek a new location for their nest. These ‘rafts’ of concentrated fire ants can be dangerous to people who encounter them unawares during a flooded, as they will swarm over the person if disturbed.
At this point in the drip floatation method, the ants can be strained from the surface of the water and moved to another container. For my research, I then divide field colonies into standardized experimental colonies with a set number of workers, queens, and brood.
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