ANTics – Part 2

By Bob Dispenza, Park and Education Manager, Allen County Parks

There was so much interesting about ants that we couldn’t fit it all in one article. This is a continuation of last issue’s article.

The main reason we can’t have giant ants (like in the old sci-fi movie “Them!”) is that insects depend on oxygen diffusing into their bodies through spiracles – holes in their sides that lead to almost every cell. Air can only diffuse so far through these tubes, and insects have no active oxygen transport system, such as lungs or gills and blood. Once insects get up to a certain size (about as big as the palm of your hand), oxygen can no longer diffuse into their internal tissues. Without oxygen, the internal cells would die and rot, killing the insect. When oxygen levels were higher in the past, insects could be larger due to increased diffusion. The insect exoskeleton also has limited strength, and large sizes would cause collapse or buckling of the plates when the insect muscles were used.

Communication is mostly chemical and tactile. Ants recognize each other by “smell” and “touch.” Other ants that don’t “smell right” are subject to attack. Alarm pheromones given off by a few can rile up the whole nest. Some information is transferred through the colony by social feeding (trophallaxis), where ants feed each other on request from a special stomach or mouth cavity. This lets the whole colony know how many ants are doing what jobs and how healthy the queen is. Some primitive ants have large eyes and hunt by sight, but most depend heavily on their antennae for chemical instructions. This limits their ability to recognize invaders and parasites – if it smells right and gives good things (honeydew or other sweet secretions), it must be OK, even if it is eating ant larvae or stored food.

Myrmecophiles (“ant lovers”) live with the ants, and are a diverse lot. Some clean the nest of dead insects or fungus, some eat food the ants have stored, and some eat ants themselves or their larvae or eggs. Some trick the ants into feeding them by chemically posing as an ant. Some reward their hosts with sweet secretions. Some myrmecophiles are never found outside ant nests, while others may live independently.

The little six-legged wonders we call ants are involved in some pretty strange ecological relationships. The lancet fluke is a parasite of many farm animals, but uses ants to get to them. The eggs from an infected animal are deposited with their dung. These are eaten by land snails, and the eggs hatch. The hatchling creatures go through several changes, eventually winding up in the snail’s mantle cavity. There they irritate the snail into surrounding them with mucus, making “slime balls,” which the snail leaves behind. Ants are attracted to the slime balls and eat them.

Most of the developing flukes inside migrate to the middle of the ant, where they become infective (can infect their final host – a farm animal). But ants mostly avoid bright light, and so are not usually eaten by farm animals. The microscopic flukes resort to mind control. One or two of them migrate to the ant’s “brain” and wrap themselves around the nerves. This causes the ant to behave the opposite of what it usually would. Instead of going into the nest at night, it stays out. And instead of staying low, it climbs to the top of grass stems and holds on with its jaws, where it remains all night. That way, when grazing animals start feeding in the morning, the ant is in a place where it could be eaten. If it is not eaten, as the sun warms it up, it goes back to normal behavior – until that evening. Eventually it gets eaten and the fluke can move to the farm animal’s liver area, where it matures and starts producing eggs.

Ant society parallels human society in some interesting ways.

Agriculture – Ants are involved in raising fungus gardens underground and in “herding” aphids and other insects for honeydew. Ant “farmers” will protect their herds from predators and move them around during unfavorable weather. The fungus some ants grow is never found outside their nests.

War - Shining amazon [Polyergus] ants cannot even raise their own young or feed themselves – they must raid other ant nests and take slaves, which are usually larvae that will recognize no other nest or masters when they mature. Since the conquerors can’t even take care of their own young, they must continually raid other nests for new slaves.

Specialization of labor – Ants have “millers” to grind grain, repletes to store excess, soldiers to repel invaders, nurses to care for young, and “aristocrats” to reproduce (but the real rulers are the workers, who control the colony through chemical communication). Unlike bees, some ants have more than one queen in a nest.

What’s good about them? Ants are on par with earthworms as soil movers and aerators. They are one of our main scavengers of dead animals and cleaners of our natural areas. So the next time uninvited guests show up at your picnic, remember how hard they work and how much they care for their sisters. They don’t eat much – throw ‘em a few crumbs!