When you go out, you'll get covered in flies and be stuck under trees. These little bugs are the most annoying in spring and summer!

I believe you must have had this experience: wearing beautiful clothes and walking outside, but inexplicably, you are covered with small flies. The clothes are new and there is no sweat smell, but these small flies come uninvited, as if they were covered with black sesame seeds. Even if you shake them off, they will fall all over again after a while...

Source: Shenzhen Health Commission

What are the origins of these annoying little bugs? Let's talk about these annoying little creatures today.

1. So, what exactly are they?

In fact, the things flying all over your body are the famous aphids. Yes, they are the aphids that are eaten by carnivorous ladybugs such as the seven-spotted ladybug.

Ladybug preying on aphids

Source: Wikipedia

Aphids, also known as "honey bugs" or "sticky bugs", belong to the order Hemiptera and are relatives of cicadas, treehoppers, wax cicadas and scales. This type of insect first appeared in the Carboniferous period. Hemiptera insects can be said to be "pests in abundance". Many agricultural and horticultural pests come from this group, such as stink bugs and our protagonist today, aphids. The aphids that people usually refer to are insects in the superfamily Aphidoidea under the suborder Sternorhynchus. In fact, aphids are a large group. Under the superfamily Aphidoidea, about ten families and more than 4,400 species have been discovered, of which more than 200 are pests that are harmful to agriculture, forestry and horticulture.

There are many common species of aphids in Beijing, including peach aphid, cypress aphid, white-haired aphid, locust aphid, cotton aphid, etc.

Aphids on plants

Source: Wikipedia

Aphids are usually small, only about one millimeter in length, but there are also species that can reach 1 centimeter in length. These insects have no wings and very thin legs. They only know how to lie on the surface of plants to suck juice and rarely crawl around.

Their mouthparts are similar to a needle. When feeding, they use this "needle" to pierce the plant epidermis to reach the sieve tubes in the phloem to suck the plant juice. As long as the "needle" pierces the plant sieve tube, the juice will automatically be pressed into the aphid's stomach through the mouth under the action of pressure. These "vampires" on plants live a comfortable life of "opening their mouths for food".

2. Why do aphids fly onto humans?

When it comes to aphids, we often imagine dense yellow-green insects appearing on green plants at home. But if you look closely, you will find that aphids at home generally have no wings, which seems to be different from those insects that fly onto people?

To explain this problem, we have to mention the reproduction of aphids.

Aphid reproduction is very complicated. In spring and summer, aphid eggs that have survived the cold winter hatch one after another. Most of the aphids that hatch at this time are female. At this stage, female aphids will reproduce parthenogenetically, that is, give birth to female nymphs directly without mating. In about 20-40 days between spring and summer, aphids can reproduce many generations through parthenogenesis. A female aphid that hatches in spring can even produce hundreds of millions of offspring!

Aphids that reproduce parthenogenetically, with a nymph being born in the picture

Source: Wikipedia

During the parthenogenetic stage, the sudden increase in the "insect population" will cause some species of aphids to produce winged females and migrate to find new suitable plants to live in. This behavior is often very concentrated, which will cause us to attract a large number of aphids looking for habitats when we go out wearing brightly colored clothes.

In autumn, as factors such as light cycle, temperature and food change, female aphids begin to give birth to male offspring for sexual reproduction and produce eggs that can survive the winter.

Life stages of apple aphid (Aphis pomi): A. Mature female B. Mature male C. Female nymph D. Female laying eggs E. Laid eggs (changes from green to black over time)

Source: Wikipedia

In addition, you may have noticed that clothes that attract small flying insects are often bright yellow. This is because different insects have preferences for different light. For example, aphids are most likely to be attracted by yellow light with a wavelength of 550-600 nanometers. In addition to aphids, insects such as thrips and blackflies are also attracted to yellow objects.

Yellow sticky insect board

Source: A shopping website

Taking advantage of this characteristic of insects, different colored sticky insect boards are often used in agriculture to control pests according to different insects.

Aphids can also use the wind to migrate over long distances, as they are extremely light and can be blown thousands of kilometers away. Some species of aphids are thought to have spread from New Zealand to Tasmania in this way.

3. There’s one more thing you hate about aphids

There are always some black water drop-shaped marks under many trees (especially Sophora japonica trees). Sometimes, there will be sticky liquid dripping like "raindrops". When you walk past, you will feel the ground is sticky. There are also a lot of sticky liquids on the bicycles and cars parked under the Sophora japonica trees. The culprit of these phenomena is aphids.

We mentioned earlier that aphids live by sucking plant sap, but the concentration of nitrogen in the sap that aphids can use is very low, so aphids need to suck a lot of sap to feed themselves. Fortunately, the sap is automatically pressed into the stomach of aphids under the pressure of the plant body, so they can drink it effortlessly and just need to digest it.

The liquid digested by aphids is excreted from their rectum. This liquid is called "honeydew" because it has a very high sugar content, which is 150 times sweeter than sugar! When countless aphids on a plant "urinate at the same time", it can even produce a spectacular scene similar to rain.

For many insects, honeydew rich in sugar is a godsend. For example, ants will consciously collect the honeydew of aphids as food.

Ants collecting honeydew from aphids

Source: pixabay

Some species of ants even collect aphid eggs to help them overwinter, and consciously "herd" these aphids. When aphids' natural enemies such as ladybugs prey on aphids, they may even be attacked by ants! In addition to ants, some bees also collect the honeydew secreted by aphids to make honey.

Ants herding aphids

Source: Wikipedia

Although the honeydew produced by aphids is a good thing in the eyes of many insects, it is of no benefit to humans.

Not only does it pollute the ground, it also drips onto the leaves of plants, affecting normal photosynthesis and even inducing sooty mold disease in plants... The most important thing is that the editor has had enough of bicycle seats that are sticky with honeydew!