Insect penises come in an extraordinary variety of shapes and sizes. Brush-shaped, football-shaped, and other fantastic structures are not unheard of. Rarely, however, do penises come in pairs. Earwigs of the family Anisolabidae are an exception.

In particular, males of the earwig species Euborellia plebeja have two penises that are often longer than the earwig's one centimetre body. One of the E. plebeja penises, or virgae, as entomologists know them, usually points inwards, so researchers previously assumed that it wasn't a functional organ. To prove that is was, Dr Yoshitaka Kamimura, of the Tokyo Metropolitan University, and his colleague Dr Yoh Matsuo, interrupted the mating of nine earwig pairs by pinching the male's backside and lifting him off the female.

Risky business - after sex a female earwig may end up with a spare penis lodged in her vagina.

The length and fragility of the earwig's penis makes it prone to breaking off during mating, especially if disturbed. Yet two days later, all nine males successfully inseminated a new female partner with their spare penis. And despite the broken virga stuck inside them, the females went on to lay eggs.

This suggested that the second virga could function as a spare. To confirm their idea, Kamimura and Matsuo collected 663 specimens of E. plejeba from the gardens of Japan. Three males had lost one of their penises, and two females had the mutilated remains of a male mishap still lodged in their vagina.

While sexual accidents among earwigs are rare, it appears to be a risk that evolution has catered for. Dr Kamimura proposes that ancient earwigs in fact used both their paired virgae at once. Another earwig Dr Kamimura is studying, Diplatys flavicollis, has males with paired virgae, and females with multiple spermathacae (the insect equivalent of a double vagina). So far the males of this species have only been observed using one of their paired virgae for mating, but Dr Kamimura is keeping an eye on them.

Though earwigs might seem kinky, they have nothing on one of insects' most maligned subjects, the cockroach. For cockroaches, peeing on each other is more than just a turn on - it assists insemination.

Cockroaches are reputed to be some of the hardiest creatures around - it's been rumoured that they could survive nuclear war. In keeping with their image, cockroaches have a ribald approach to courtship. What else would you expect from an insect that can live for nine days without its head?

Courtship begins with the use of pheromones, the hormonal messages that insects, and most other animals, including humans, use as one way to communicate with each other.

Male pheromones entice a female cockroach to manoeuvre into a pre-copulatory position, and chemically inhibit her movements, keeping her frozen to the spot.

But the female still gets to play an active (if off-putting) part in the mating ritual. Excited by the pheromones, she begins to rub, or even eat, the male's dorsal glands.

This in turn stimulates the male to push backwards, grasp the female's genitalia, and swing her around until the pair winds up in the standard insect mating position, joined end to end. They remain like this for some time (possibly several days).

Towards the end of mating the female receives the male's spermatophore - a capsule of sperm - as well as a dose of uric acid from the male's urine. This effectively hardens the spermatophore, and helps to keep it in place.

After a few days the empty spermatophore and attached uric acid may drop out. Far from being disturbed by this sticky mess, females of the species Blattella germanica then eat the deposit, while females of the species Xestoblatta hamata actually eat it while it's still attached. The nitrogen from the uric acid is incorporated into their special egg pouch, providing nutrients for the unborn baby cockroaches.

But not all sexual reproduction in the insect world is strange or kinky. Some of it is downright vicious. Take the case of fire ants, Australia's most recent and infamous feral invader.

Fire ants maintain a multi-queen system, with several queens inhabiting a nest at once. Certain queens in the nest carry a particular gene that is both a curse and a blessing - it make the queens more fertile, but also sends a chemical signal to the nest that results in their execution.

The gene carried by the queen causes a pheromone to be released under certain environmental conditions - the chemical equivalent of an execution order. Scurrying around the nest, antennae quivering, ant workers pass on the pheromones like an underground revolutionary movement: the queen must die. After the execution, just the legs of the unfortunate royal remain.

Dr. Kenneth Ross from the University of Georgia, and Dr. Laurent Keller, from the Universities of Bern and Lausanne (Switzerland), believe that the fertility of these gene-cursed queens is a threat to the genetic diversity of the nest. A nest with limited gene diversity is more vulnerable to attack from parasites and diseases.

In single queen nests, such as those of the black meat ants found in suburban kitchens, the queen has a remarkable method of ensuring her sexual dominance. The queen secretes a substance that oozes all over her body. Her daughters, the all-female soldiers and workers that make up the nest, find the substance irresistible and lick the queen's body.

The substance the queen secretes poisons her daughters - not to kill them, but make them infertile.

This provides a simple solution to the problem of secession. When a queen dies, her daughters lay unfertilized eggs, which become males. One daughter takes over as the new queen, mates with the short-lived males, and her progeny become the worker females that keep the empire going. And so the process continues.

Although it seems strange that the workers so readily sacrifice their own capacity to pass on genes, ants share 50 percent of their genetic material with their mother and 75 percent with their sisters. Genetically it makes sense for workers to look after their sister workers, rather than putting energy into any attempt to produce daughters of their own.

For one native Australian wasp, reproduction can be an uncertain experience, thanks to an ingenious orchid.

The female orchid of the species Chiloglottis trapeziformis dresses itself as an attractive female wasp and it uses the same perfume! They exactly mimic the appearance and pheromones of a female wasp of the species Neozeleboria cryptoides.

This is devastating for the female wasp which is wingless and relies solely on pheromones to attract flying males. They also rely on the chivalrous males to carry them to a food source, and deposit them somewhere appropriate for egg laying.

The pheromones released by the orchids attract male wasps, and the visual nature of the mimicry provokes male 'pseudocopulation'. An unlucky guess by the wasps leads to pollination of the orchid. In case you were wondering, pseudocopulation is just what it sounds like - fake sex.

Bob Wong and Florian Schiestl, both from the Australian National University's School of Botany and Zoology, have showed that the male wasps avoid orchids that have previously led them astray.

Unfortunately this disadvantages the flightless female wasps that inhabit areas where orchids of the genus Chiloglottis grow. Wong and Schiestl found that the male wasps don't just avoid the particular chemical signal released by the orchids they avoid the entire area.

For the orchid, prostitution for pollination can involve a long wait: just 13% of male wasp visits lead to pseudocopulation. For the male wasp, the visit is just as unrewarding. Even when contact between the male wasps and orchid is made, ejaculation is rarely observed. It's a waste of energy for the male, so no wonder the number of visits made by the males to the orchid area decrease over time.

The advice to female wasps is to strut their stuff a little further from the competition.

The reproductive behaviours of insects are examples of the quirkiness of evolution. The earwig with a spare penis, the fertile queen ant containing a genetic code for self-destruction, and even the cockroach have each evolved behaviours over time that pass on some advantage to the next generation. Evolution has clearly paid off for insects; they are by far the most diverse group of animals.

Insect reproduction is a fascinating world of discovery where anything goes. And that's without mentioning the sexual cannibalism of praying mantids. Next time you see one of these six-legged critters crawling around, hold the spray for a minute and contemplate just what they've been through to get there.