Fascinating bugs caused ladybird boom

APHIDS are soft bellied, slimy-looking bugs, rather less than half a centimetre in length and not the kind of thing you want to find in your hair.

They are the enemy of gardeners and farmers because the black beaned variety will ruin beans, cabbages, peas and mangolds by sucking the sap from the plants and by carrying viruses around the countryside.

Crops of potatoes and sugarbeet suffer in particular.

You may well wonder why these tiny pests should qualify for comment in two successive months of Nature Watch.

The fact is that they do have some remarkable characteristics.

The first is the prolific reproduction rate of the little pests.

In a single year one aphid’s descendants would equal the weight of 600 million humans if they all survived - more than half the population of India.

Fortunately nature has made them prey of ladybirds, small birds like blue tits and other insects, such as lacewing, which consumes huge numbers of them.

Those that survive will be changing their abode about now from bean-plants to spindle trees, which are their favourite haunt for the winter.

This involves hitching a lift on the convectional currents of warm air, which may take them a mile or so up in the air to some mystery destination.

Thermal currents tend to die out in the evenings so along with fellow hitch-hikers, spiders and mites, they will drift to the ground.

They might be unlucky and land in the Alps or Birmingham Bull Ring, but they have a good chance of making it to some rural area and finding a spindle tree.

The winged females that make it to their winter abode now perform an amazing feat called parthenogensis - which literally means ‘virgin birth’.

The offspring will then mate with the males of the party that made it back to the spindle tree and the females will lay eggs that will survive the winter.

The eggs hatch out around March into wingless females, also using the ‘virgin birth’ process, but there will be no males.

A few will have wings, and these will be the ones that fly off in the earl summer to start new colonies in our vegetable plots.

There will follow new generations alternating between winged and wingless, all born without the involvement of a single male or egg.

In a lifetime of two to three weeks, a typical female will give birth to about 80 offspring, starting from when they are around eight days old.

If your calculator is up to it, you will soon find yourself in the multi-millions when it comes to working out the total progeny of any one aphid in a year.

They must have real problems thinking up names for them all.

The infestation of ladybirds along our coast in August was the inevitable result of a build-up of aphids.

Warm thermals from the continent, or maybe from inland areas dumped great showers of them on our sands and open spaces.