Wednesday, 5 November 2008

The Weird Life Cycle of the Ladybug

The Ladybug has something of a strange life cycle and one that surprises many people. From egg to fully grown ladybug, join us on a journey of a lifetime - literally!

The ladybug will always try and mate as close to a colony of aphids as possible. When its larvae hatch they will then have a ready made food source upon which to feast. When the eggs are laid they are only about a millimeter in length and the numbers can range from a few right up to several hundred, depending on the conditions.

The male has an insect penis which is called an aedeagus. A “lock and key” fit means that if he gets it wrong and tries to mate with another species of ladybug, he will not get to third base! Fertilization, as you can see, is internal, which surprises many people. It doesn’t exactly start with a kiss, but with a little Barry White in the background this could almost be classed as romantic! Almost, but not quite!

Harmonia axyridis lays its eggs. Many people believe that the ladybug will lay the same amount of eggs each time it mates. This would be true if conditions were always at a constant: what happens is that when conditions are harsh, the ladybug will lay many eggs that are infertile. Only laying a few eggs that will hatch is not just to maximize the chances of survival of those that are fertile, however. The infertile eggs will actually provide sustenance for the lucky ones who survive through to hatching before they start roaming for live prey. If times are harsh, however, this particular species will gladly feast on the eggs of other ladybugs and different species of insects.

This particular set of eggs belongs to the species Harmonia axyridis which is also known as the Harlequin Ladybug or Asian Lady Beetle. It was first introduced to North America and Europe by man in the early twentieth century as a way of controlling scale insects and aphids, which it devours readily and in huge numbers. In some parts of America it is also known as the Halloween Lady Beetle because it is found in many homes in the month of October. This is because it likes the warmth of human habitation and so is drawn their for its winter hibernation period (yes, Ladybugs hibernate!).

Hatching takes place after three to five days, which is pretty quick, even for an insect the size of a ladybug! Six legged larvae about one eighth of an inch emerge and start devouring as many aphids as they can – they have quite a metamorphosis to undergo before they are adult and they need as much food as they can get! If the conditions are right, then the larvae will grow very quickly. The whole process from egg to adult can take as little as twenty four days.

The ladybug larva goes through several stages and is best described as looking something like an insect equivalent of a crocodile, only black and with (occasionally) orange markers. The larvae eat about twenty five aphids (or equivalent!) a day. That’s nothing to what the adult can get through – roughly about fifty. This is why many ladybugs are popular with farmers and gardeners. In fact their name comes from a time in the Middle Ages when people thought that they were sent as a gift from the Virgin Mary to help with controlling pests. It is not, as many people believe, a protogynous hermaphrodite. This is when an animal begins its life as a female. So, if you thought they were so named because the vast majority (or as some believe, all of them!) were female, then put that thought out of your mind!

Many people assume that the ladybug – adult and larva alike – have only one food source, that is the aphid. Again, this is not true. They will eat scale insects (such as the cochineal). They will also make a tasty meal out of any mealybugs they come across (mealybugs are unarmored so make an easy and tasty meal!). They will also eat mites, which to our eyes are pretty much invisible, but to a ladybug will make the equivalent of an in-between meal snack! Does the (some would say poor and unfortunate) aphid have any protection? The only defense it has is gravity! Aphids will simply let themselves fall off the leaf if they can, and plummet to the ground, in order to escape being on the day’s menu.

There isn’t much respect between the species, either! Here, a Harlequin ladybug makes a meal out of one of the smaller native ladybugs in a US garden. The Harlequin is becoming such a nuisance in some places – and a threat to local biodiversity because of its size and voracity – that ways of getting rid of the species from Europe and the US are being looked in to. This may involve the introduction of its natural parasites from Asia. Let us hope that the home grown species are immune!

When the larva has grown to its full size it will then attach itself to the stem of a plant. It splits along its backside and exposes the pupa underneath. This sounds like something out of one of the “Alien” films and it really doesn’t take long to figure out that they didn’t get those ideas straight out of their imagination! The pupa, though, is wrapped up in this final stage of its metamorphosis and so is safe from the elements – but not from predators. It is at this stage it is at its most vulnerable. If it approached close to its hatching time by a possible predator it will shake itself dementedly to try and warn off the unwelcome visitor! This last stage takes just a few days and then the adult ladybug is ready to emerge.

Like any newly hatched insect, the ladybug must take some time to ‘dry out’. When it emerges it is completely soft and its exoskeleton and elytra (see below) must harden. This is made of chitin, which is a protein much like the one that creates our fingernails. For the first twenty four hours or so the ladybug will have no spots. Then it will go and find its first meal. Recently, four ladybugs and a whole heap of aphids were sent up in to space to try and ascertain how the aphid would try and escape from its enemy without the assistance of gravity. With some time to while away, the astronauts (on a 1999 mission) gave the four bugs names: John, Paul, George and Ringo. The result of the experiment? Ladybugs do very well in space, aphids don’t! Quel surprise!

Adult ladybugs come in a variety of colors and these are no accident. In nature there are colors that warn off potential predators. The main colors that the five thousand (or so) species of ladybugs have are red, black and yellow. Unsurprisingly, these are exactly the colors that tell would be diners that this dinner is not going to taste very pleasant! Ladybugs also have one other trick up their sleeve. They ‘play dead’. They pull their six legs up so they cannot be seen and do a ‘reflex bleed’. This is when they excrete a little amount of their ‘blood’ (which is yellow and smells horrible to predators). Anyone reading this that could once have been classified under the genus “boy” and who had a fascination with insects will recognize this little trick of the ladybug!

The ladybug uses the part of its body which gives it its color for more than just protection from predators. The elytra (if you can’t remember that, then you can call them shards) on its back are actually a modified forewing. Instead of using it to fly, the ladybug uses it to protect its hind wings, which are positioned underneath. Although it can get battered over time, it usually ensures that the ladybug retains the power of flight for the duration of its life (which is usually anything up to nine months). In some species of bugs the elytra fuse with the hind wings – and so we have the thousands of varieties of insects that cannot fly!

This of course, is not the case with the ladybug. It is one of the most popular insects on the planet (certainly among children) and has found itself at the center of many a myth and legend – as well as the occasional nursery rhyme. As the next generation flies off to feed and mate, perhaps it is appropriate to end with the most famous (in the English language at least). We will leave it intact, with its original UK English name – “ladybird”.

“Ladybird, ladybird, fly away home

Your house is on fire and your children are gone

All except one, and that's Little Anne

For she has crept under the warming pan.”



Glynis said...

I am always glad to see a ladybird on my veggie patch! Thanks for educating me further on these cute bugs

Anonymous said...

A huge swarm of those critters, hundreds-of-thousands of 'em, landed on my little brother one day and began eating him.

Amidst his piercing screams of agony I heard the chitter chatter of a multitude of mandibles as his flesh was rent asunder.

Within minutes his bare bones lay upon the ground as the swarm arose, departing, apparently seeking a new victim.

I suppose my larger size kept those bugs away from me.

Ma and Pa didn't miss him until I brought the event up a couple weeks later. It's like that when us share-croppin' folks live in a shanty with a dozen kids clustered within. One less mouth to feed and clothe is no huge loss.

Kinda' miss bro', though. He was fun to throw rocks at.

Joel said...

Chitin is not a protein, the way keratin is.

It is a polysaccharide, like starch or cellulose. The dietary fiber in mushrooms is chitin.

susi said...

Greetings...these pictures are lovely, thank you for sharing...