Many insects camouflage themselves to avoid predators. Such is the case with the larvae of several species of Green Lacewings (Family: Chrysopidae) that place debris upon their back. Recently Jim Davis and I documented one species at different stages of its development, including young hatchlings, larvae eluding ants, pupae, and the light green adults after they eclosed (see photos). The behavior of the carnivorous larvae, called aphid lions, is particularly fascinating.

   The green lacewing species we observed lays eggs in a spiral pattern typically on the surface of a leaf. Since each egg is deposited at the end of a stalk (see photo), emerging larvae are partially protected from voracious siblings which have already hatched and, perhaps to some degree, from ants as well. New hatchlings -- covered with bumps and spiny setae -- promptly stuck debris on their back, including empty egg cases still attached to stalks. The fact that the tiny larvae that we observed spent so much time trying to cover themselves suggests that being adequately disguised is critical to their survival. But why? Their preoccupation with stalks and egg cases also suggests that these items have particular value; perhaps they are coated with an ant repellent. Once the lions moved further afield, however, some switched to attaching the molted skins of their prey upon their back. As shown in the video, much of the debris placed on the back of aphid lions adheres to a dark-colored hump located near the posterior end of the insect. As more debris accumulates, a jumbled mass of aphid carcasses, lichen, etc., will eventually cover a larva's entire dorsal side.

   In a glass jar containing lacewing larvae, I inserted several twigs infested with aphids, which I hoped the lions would eat. The ravenous insects readily attacked the aphids, piercing their prey with sickle-shaped mandibles, which are hollow for sucking out the bodily fluids of their victims. More benignly, they were also observed sipping on honeydew secreted by aphids (see video).

   When a resting aphid lion is approached and probed by one of its siblings, it rocks back and forth, presumably to signal that it is not idle debris to be harvested. On the other hand, when approached by a curious ant, an aphid lion lowers its head while raising the hump on its back (see video), a maneuver that can extend the debris on its back over the larva's head--assuming, of course, enough debris had been collected. The aphid lions I observed performing this defensive posture remained perfectly still until the ant moved away.

   It is commonly known that many aphids are tended by ants because they copiously secrete sweet honeydew that ants relish. In return for food, the ants ward off predators such as aphid lions. Such an arrangement, however, is not a perfect defense, as we discovered when a mature aphid lion raided a colony of aphids.

   As the lacewing larva advanced toward an aphid colony, none of the ants walking along the same vine seemed to recognize the potential threat. While some ants harvested honeydew, others that encountered the aphid lion, now only a few inches from the colony, simply probed the predator with their antennae before moving on. In response to the ants, the aphid lion defensively crouched until the coast was clear, and then continued its trek toward the aphids. Apparently possessing a sizable amount of debris on its back presents an effective shield against ants. However, once the carnivorous larva reached the aphid colony, interactions between the predator and the prey's benefactors intensified.

   Initially, the aphid lion managed to pierce an aphid before the ants detected something was amiss. Only then did the ants relentlessly tear away bits of the debris from the lion's back until eventually the predator was forced to retreat. We can only presume that the aggressive behavior of the ants was triggered by an aphid releasing an alarm pheromone. Also, late in the assault, two ants sprayed formic acid in the direction of the departing aphid lion. We cannot be certain that only ants prompted the aphid lion to depart, because their effort was inadvertently helped by a second aphid predator, a Syrphid fly maggot, already surreptitiously feeding on the aphids (see video). Why the ants ignored the maggot feeding on an aphid is unknown. As far as we could discern, the maggot lacked any visible defenses.

• Aphids release an alarm pheromone when threatened.

• Aphid lions eat not only aphids, but also other soft-bodied insects.

• Lacewing larvae are considered to be beneficial insects by farmers and gardeners and are commercially farmed.

• Aphid lion eggs are typically laid near a source of food.

• In some green lacewing species, the egg stalks are coated with a nutritious oil.

• Do the egg cases of aphid lions contain a chemical ant repellent?

• Hatchling aphid lions avoid older aphids. Is this because the skin of older aphids are too tough for a newly eclosed larva's mandibles to pierce?

• Do aphid lion eggs hatch simultaneously?