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10 Fascinating Facts About Aphids

10 Reasons Aphids Don't Suck

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Aphids have tailpipes, called cornicles.

Aphids have tailpipes, called cornicles.

Flickr user aroid (CC license)
Where you find aphids, you'll often find ants feeding on the sweet honeydew left behind.

Where you find aphids, you'll often find ants feeding on the sweet honeydew left behind.

Photo: © Debbie Hadley, WILD Jersey

As the joke goes, aphids suck. And while this is both literally and figuratively true, in some respects, any entomologist will tell you that aphids are actually interesting and sophisticated insects. Check out these 10 fascinating facts about aphids and see if you disagree.

1.  Aphids poop sugar. Aphids feed by piercing the phloem tissue of the host plant and sucking up the sap. Unfortunately, sap is mostly sugar, so an aphid must consume a lot of sap to meet its nutritional requirement for protein.  Much of what the aphid consumes just goes to waste. The excess sugar is eliminated in the form of a sugary droplet called honeydew. An aphid-infested plant quickly becomes coated in the sticky excretions.

2. Some aphids are tended by sugar-loving ants. Anyone who has battled sugar ants in their kitchen can tell you that ants have a sweet tooth. Ants are therefore very fond of bugs that can poop large quantities of sugar. Aphid-herding ants will actually care for their adopted aphids, carrying them from plant to plant and "milking" them for honeydew. In exchange for the sweet treats they get from the aphids in their care, they provide the aphids with protection from predators and parasites. Some ants even take the aphids home to their nest during the winter months, keeping them safe until spring.

3. Aphids have a lot of enemies. I'm not just talking about gardeners, either. Aphids are slow, they're plump, and they're sweet to eat (presumably). A single plant can host hundreds or even thousands of aphids, offering predators a veritable smorgasborde of snacks. Aphid eaters include lady beetles, lacewings, minute pirate bugs, hoverfly larvae, big-eyed bugs, damsel bugs, and certain stinging wasps, among others. Entomologists even have a term for the many insects that feed on aphids – aphidophagous.

4. Aphids have tailpipes. Most aphids have a pair of tubular structures on their hind ends, which entomologists describe as looking like tiny tailpipes. These structures, called cornicles or sometimes siphunculi, seem to serve a defensive purpose. When threatened, an aphid releases a waxy fluid from the cornicles. The sticky substance gums up the mouth of the predator in pursuit, and is thought to trap parasitoids before they can infect the aphid.

5. Aphids sound an alarm when they're in trouble. Like many insects, some aphids use alarm pheromones to broadcast a threat to other aphids in the area. The aphid under attack releases these chemical signals from its cornicles, sending nearby aphids running for cover. Unfortunately for the aphids, some lady beetles have learned the aphid language, too. The lady beetles follow the alarm pheromones to locate an easy meal.

6. Aphids fight back. Aphids may look defenseless, but they don't go down without a fight. Aphids are expert kick boxers, and will pummel their pursuers with their hind feet. Some aphids bear spines that make them challenging to chew on, and others are simply thick-skinned. Aphids are also known to go on the offensive, stabbing the eggs of predatory insects to kill their enemies in vitro. If all else fails, aphids simply stop, drop, and roll off their host plant to escape predation.

7. Some aphids employ soldiers for protection. Although not common, certain gall-making aphids produce special soldier nymphs to protect the group. These female guards never molt into adulthood, and their sole purpose is to protect and serve. Aphid soldiers are fiercely committed to their job, and will sacrifice themselves if needed. Soldier aphids often have burly legs with which they can detain or squeeze intruders.

8. Aphids lack wings (until they need them). Aphids are generally apterous (wingless), and unable to fly. As you might imagine, this can put them at a considerable disadvantage if environmental conditions deteriorate, since they aren't very mobile. When the host plant becomes a little too crowded with hungry aphids, or if it's sucked dry and there's a lack of sap, the aphids may need to disperse and find new host plants. That's when wings come in handy. Aphids will periodically produce a generation of alates – winged adults capable of flight. Flying aphids don't set any aviation records, but they can ride a wind gust with some skill to relocate.

9. Female aphids can reproduce without mating. Because aphids have so many predators, their collective survival depends on their numbers. A quick and easy way to boost the population is simply to dispense with the nonsense of mating. Female aphids are parthenogenetic, or capable of virgin births, no males required. Like Russian nesting dolls, a female aphid may carry developing young, which are themselves already carrying developing young. This significantly shortens the development cycle and increases population numbers rapidly.

10. Aphids give birth to live young. You might expect a bug that seems so primitive to lay eggs like more other insects do, but aphids are pretty sophisticated when it comes to reproduction. There isn't time to wait for eggs to develop and hatch. So aphids practice viviparity, giving birth to live young. The aphid's eggs begin to develop as soon as ovulation occurs, without any fertilization.

 

Sources:

  • Insects: Their Natural History and Diversity, by Stephen A. Marshall
  • Encyclopedia of Entomology, 2nd edition, edited by John L. Capinera
  • Aphid Ecology: An Optimization Approach, by Anthony Frederick George Dixon
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