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Pencils that rub, the dearth of male ants, how queens make queens

Q: How do pencils write? — Julia, Washington DC

The oldest pencil, lost by a carpenter in the 17th century and found in the roof joists of a house. [Faber-Castell USA]

A: You make a pencil mark by stroking soft ‘lead’ (actually, graphite, a dark grey mineral) over the writing material — usually paper. The fibers of the paper rub off graphite particles, which stick to the paper. This is a different operation than painting with a brush or writing with a pen (which coats or stains the paper).

From 500 to 300 B.C., Egyptians used the first tools later called ‘pencils’ but the pencils painted or inked. They didn’t rub graphite like modern pencils and were made of hollow reeds and tiny brushes. Romans named the writing instrument, ‘pencillus’, Latin for ‘little tail’.

In 20 B.C., Philip of Thesalonica, a Greek poet, described writing tools made of lead disks. This is the oldest mention of a pencil-like tool.

In 1564, the modern pencil was born. A great storm blew down a tree in northern England (Cumberland) and exposed a black mineral at the tree’s roots. The local townspeople started marking sheep with it and called it ‘plumbago’, which is Latin for ‘acts like lead.’ Two hundred years later the Swedish chemist Carl Wilhelm Scheele showed that the mineral is graphite, a crystalline form of carbon, not lead.

By the way, the average pencil can draw a line 35 miles (56 km) long.

Further Surfing:

Faber-Castell USA: Pencils

The pencil pages: pencil history and lore

The Cumberland Pencil Museum: The history of Cumberland graphite

The dearth of male ants

Q: In documentaries about ants, the soldiers and worker ants are both classified as female. If the queen is the only one that lays eggs, why are the others identified as female? Also, how many male ants exist in a colony or are the queens like black widow spiders? — David, Warwick, Rhode Island

The head of a black carpenter ant. [Jim Kalisch, University of Nebraska, Entomology Department]

A: Generalizing about ants is risky. Trillions of ants crawl Earth’s surface — 8,000 species! But, here’s the usual case.

Typically, the queen is the only egg layer in a colony. The other females cannot reproduce because they have shrunken, undeveloped ovaries . Workers are sterile females but female, nevertheless.

The number of males in a colony varies. Consider, for example, the carpenter ants — a common ant found in old stumps, fallen logs, and houses. A few winged males and winged fertile females, born in the spring, swarm out of the colony to mate in flight. The males die shortly afterwards, but not because the queens are like black widow spiders. Males just live a short life. So, in the springtime, until mating, the colony has a small number of males.

Each female tries to found a new colony. Not all succeed. Let’s follow one queen. She finds moist dead wood and lays up to 20 eggs. All of the eggs become female sterile workers. The queen continues laying female-sterile eggs. After a few years, thousands of sterile workers crowd the successful colony.

Having populated a colony, the queen starts new colonies. From the time the young queen founded the colony until now, no males existed. In the spring, she lays eggs that develop into winged males and winged fertile females. The kings and queens swarm out of the colony and mate midair. The cycle repeats each spring.

So, after the first few years, a few males exist for a short time each spring — only when they’re needed to start new colonies.

Now, a word about exceptions to the "sterile female worker" generalization — the non-typical ant species. A few species have worker females that can produce eggs, but only male eggs. (Male eggs are unfertilized.) Even more rare: some ant species have no queens. Female workers in these species actually mate and reproduce.

Further Surfing:

University of Nebraska: Black carpenter ant images

American Museum & Natural History: The ant colony cycle

How queens make queens

Q: What causes a queen ant to lay queen eggs instead of worker eggs? How does she make queens, kings, and workers? — Shirley, Sequim, Washington

A queen carpenter ant with her brood [Jim Kalisch, University of Nebraska, Entomology Department]

A: A queen controls egg sex and ant caste (queen, king, or worker) mostly through a clever use of sperm. She acquires a bag of sperm that lasts her lifetime (10 to 30 years) when she swarms as a young ant. She selects suitable partners and mates with several males so her sperm bank has good genetic material.

A queen controls an egg’s sex by fertilizing or not fertilizing the eggs. Females come from fertilized eggs and males from unfertilized eggs. The males can mate and therefore are kings, for a few short days.

Females come in two types: sterile workers and fertile queens. A queen controls which female type emerges through the genes she passes along. Actually, she doesn’t have absolute control over this process and can’t or sterile workers would cease to exist in a few generations.

Any sterile caste whose genes invariably caused sterility could not be passed on and, therefore, those genes would quickly be eliminated from the population. Thus, the genes for sterility are expressed conditionally — they may or may not cause a female to be sterile. Genes don’t dictate what happens. Instead, genes have to be turned on and, in the case of queen ants, food plays a big role.

The environment of the larva decides which way the genes get expressed and whether or not the female becomes fertile. When she gets enough food (or perhaps some other physiological trigger), the larva increases hormone levels and this starts sex-organ development for the adult. A queen emerges.

By the way, the genes of the father ant determine whether a worker becomes a small worker or one large enough (twice the small worker size) to be a warrior or heavy-duty worker.

Further Surfing:

Proceedings of the National Academy of Sciences: Genetic determination of the queen caste in an ant hybrid zone

Genome News Network: Genes play role in ant social status

(Answered Dec. 12, 2003)