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Everyone likes to have friends. Associations with other individuals can be pleasant, useful, and sometimes crucial to one's wellbeing. Building relationships is a major factor in the lives of many mammals, including ourselves. And it gets really interesting when the pairing reaches beyond the species boundaries. Innumerable stories about people and dogs illustrate interactions that range from the heartwarming to the amazing, as do accounts of birds and mammals, fish and birds, and even predators and prey.

But what about invertebrates? Considering that insects have little in the way of brainpower, it is obvious that movies such as "Antz" and "A Bug's Life" take a bit of artistic license when it comes to portraying relationships. Well, and the fact that those insects can talk and do a lot of things that most people find challenging. As engaging as the characters appear, they are, remember, just animated fictional creations.

Ant & Aphids

Ants & Mealybugs

Real life insects, however, do sometimes have rather remarkable associations, and one taxon stands out as a major player in these situations: ants. There are relatively few highly social insects compared to the multitudes of solitary species. Eusociality is the rule for termites, but it is most widespread in the hymenoptera, especially honey bees and the family Formicidae.

Ants are some of the best defended insects. They live in colonies where they enjoy the advantages bestowed by sheer numbers. The female workers and soldiers communicate with each other, have sharp jaws that they readily use against prey and adversaries, and many have stingers (an ovipositor modified to deliver venom, such as formic acid or alkaloids). Anybody who has been stung by the Imported Fire Ant, Solenopsis invicta, knows the effectiveness of such stings.

Ants & Butterfly Caterpillars

Since insects do not form bonds based on intellectual stimulation, pleasure or strategic accumulation of wealth, their pairings occur through the pragmatic advantages to survival. Aphids and mealybugs are parasites that feed on plant liquids, often forming large colonies when resources are optimal. These small, soft-bodied insects reproduce quickly but have little in the way of defenses against their predators. As aphids feed, they excrete extra carbohydrates in a sugary liquid politely called honeydew, but which is actually just bug pee. Various kinds of ants find this substance irresistible and will seek out the producers, spending a lot of time sipping liquid from the aphids' butts. If a wasp, fly or person's finger gets too close to the object of their desire, the ants attack. This mutualism obviously benefits both parties, an exchange of a treat for protection. There is even evidence that the honeydew is somewhat addictive, as some research has shown that ants partaking of it often return less frequently to their nest and neglect other duties.

A similar relationship with ants occurs among some butterfly caterpillars. Like aphids, the larvae of hairstreaks and blues in the family Lycaenidae, are very slow moving and tend to just sit on their plants while feeding. They, too, ingest more liquid than they need and so generate the sweet waste product that lures ants. It's interesting to note that the ant species attracted to the herbivores range from very tiny to rather large, and there is no guarantee that any particular caterpillar or aphid colony will even have attendants. The association occurs often enough, though, that the advantages have favored its evolution.

Ants, Aphids & Lady Beetle Larvae

So what happens if no ants are guarding aphids or if their attentions are inadequate to protect their defenseless little charges? Plenty. There is a reason that aphids have evolved rapid reproduction, which, by sheer multiplication, can usually counter the ravages of predators and parasitoids and ensure the species' survival.

As the ant/aphid relationship developed, so did the aphids' predators' arsenal of ways to deal with the ants. Many kinds of lady beetles specialize in eating aphids. This is why they are a popular biological control among gardeners. Lady beetles are predators both as adults and as larvae. In fact, the immature beetles probably eat more aphids as they grow and develop than the adults who must also spend time mating and laying eggs. Lady beetle larvae usually just crawl up to an aphid and eat it. An ant might object to that, though, and drive the beetle away. Some lady beetle larvae have a counterstrategy and produce waxy coverings that chemically hide them from the ants. The secretions the beetles produce not only look a lot like those of mealybugs but evidently also fool the ants, as they ignore these interlopers that are feasting on their aphids. The aphids, in turn, seem to have no clue that their neighbors are being gruesomely devoured and they are probably next. The "wolf in sheep's clothing" seems an apt metaphor here.

Ants, Aphids (Alive & Parasitized), Lady Beetle Larva & Flower Fly Maggot

More woes can befall aphids, even as the ants wander among them, seeking a sweet sip. The final image shown here has a lot going on, and it is all occurring on a stage only about 1/2 inch long. The ants have found one live aphid among several swollen corpses. There are also a few live aphids at the lower right. Those balloon-like bodies in the center are aphids that had the misfortune to have a female wasp lay an egg into them. The minute wasp grub develops inside the aphid's body, eventually pupating and emerging from the empty shell. The aphids at the upper left are dead and have wasps inside them, while those at the upper right are just the discarded husks left behind. As if this little aphid colony is not supporting enough diversity, there are also two predators investigating. The relatively large white form at lower left is a lady beetle larva and to the upper left of it is a slender yellowish-brown flower fly maggot, yet another aphid predator. They are currently only in the vicinity of the carcasses, but will eventually move on to the live targets at the right.

In our sophisticated anthropomorphic imaginations we can easily project how horrible all this carnage is, sympathizing with the victims and their not-always-so-effective protectors, but in the entomological realm, it is more like business as usual. Remember, they are just bugs.

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