Can you tell the difference between male and female ants?
I was at my Nana's house recently and she's had issues with sugar ants. I say issues, because ultimately we're not fond of them, but also understand they are looking for food and water, and you can hardly blame an animal in search of basic survival.
It is interesting to watch them troop along once they've found a small piece of sourdough or a line marching straight to the sink. Then you see a random ant scouting out the next "big" lead. I've been more conscious about calling animals "girls" when I don't know for sure, but then I start to wonder if there's a way to tell the difference. So here we are with another Daily Doodle question waiting to be answered.
Ants, like bees, are mostly female. Ants have a caste system, where responsibilities are divided. The non-mating females raise the babies, gather the food, maintain and expand the nest, and look after the founder of the colony, the queen, who does nothing but lay eggs continuously. Worker ants are all female, and this sisterhood is responsible for the harmonious operation of the colony.
The vast majority of eggs develop as workers, but once the colony is ready the queen produces the next generation of reproductives which will go on to start their own colonies.
A female ant’s fate to become a worker or queen is mainly determined by diet, not genetics. Any female ant larva can become the queen – those who receive diets richer in protein. The other larvae receive less protein, which causes them to develop as workers. Queen ants in some species are bigger than workers; in others you have to look for the difference by examining the thoraxes -- queens have bigger thoraxes with more parts as a result of having wings for part of their lives.
Males are smaller than females, with smaller heads and longer antennae. They also have wings. Unless you dig into an ant colony, it's unlikely you'll ever see a male ant except on one special hot, humid day in early summer, after the spring rains have passed. That's when all the male ants come out and use their wings in a glorious day of free love.
Male ants have a mother but no father. Unlike humans, with X and Y chromosomes, an ant’s sex is determined by the number of genome copies it possesses. Male ants develop from unfertilized eggs so receive no genome from a father. This means that male ants don’t have a father and cannot have sons, but they do have grandfathers and can have grandsons. Female ants, in comparison, develop from fertilized eggs and have two genome copies – one from their father and one from their mother.
Male ants only have one genome copy, meaning every one of their sperm is genetically identical to themselves. And their job is over quickly, dying soon after mating, although their sperm live on, perhaps for years. Essentially their only job is to reproduce.
When the conditions are warm and humid, the winged queen and males leave their nests in search of mates. Mating takes place on the wing, often hundreds of feet up (hence the need for good weather). Afterwards, queens drop to the ground and shed their wings, while males quickly die. Mated queens choose a nest site and burrow into the soil, made softer from recent rain.
One leaf cutter species (Mycocepurus smithii) has evolved to do without sex at all -- the queens clone themselves, while some unmated females lay eggs that produce only winged males, who leave the colony.
Once underground, the queens will not eat for weeks... that is until they have produced their own daughter workers. They use energy from their fat stores and redundant flight muscles to lay their first batch of eggs, which they fertilize using sperm stored from their nuptial flight. It is the same stock of sperm acquired from long dead males that allows a queen to continue laying fertilized eggs for her entire life. Queens never mate again.
After establishing her colony, the queen’s work is not done and she has many years of egg-laying ahead of her. In the laboratory, L. niger queens have lived for nearly 30 years. Workers live for about a year, males little more than a week (although their sperm live longer). These extraordinary differences in longevity are purely due to the way their genes are switched on and off.
Sometimes two queens unite to found a nest. This initially cooperative association (which increases the chance of establishing a colony) dissolves once new adult workers emerge and then the queens fight to the death. Colonies sometimes steal brood from their neighbors, putting them to work as slaves. Slave-making has evolved in a number of ant species, but they also display cooperation at extraordinary levels. An extreme example of this is a “supercolony” of Argentine ants (Linepithema humile) which extends over 6,000km of European coastline from Italy to north-west Spain, and is composed of literally billions of workers from millions of cooperating nests.