While hustling a group of first and second graders along the trail to get them back to their bus on time, I hit the breaks when my eye was caught by masses of white fuzz in the alders along the boardwalk. I zoomed in on the fuzz, with the kids right beside me. What could it be? When I got close enough, I knew what we had: woolly alder aphids (Paraprociphilus tesselatus).
Usually we see these insects in late summer and early fall when the bits of white fuzz start flying around. They are kind of pretty, in a fluffy faerie sort of way, with just a hint of pale blue showing through the fuzz. But, they are aphids, after all, and we all know that aphids tend to be bad news for plants.
In preparation for writing this post, I read up on woolly alder aphids, and it turns out that, like so many things on this planet, they are pretty interesting characters. For example, let’s look at that glorious white fuzz. It’s more than just a pretty covering. This cottony fluff is actually a waxy substance that the aphids exude to protect their juicy grey bodies from predators. After all, if you were looking for a mouthful of tender insect, and instead you got a mouthful of waxy fuzz, you might think twice about snacking at this location.
But every problem has a solution, and indeed there are two major predators of these aphids: the larvae of green lacewings (Chrysopa slossonae) and the caterpillar of a butterfly appropriately known as the Harvester (Feniseca tarquinius). This caterpillar, by the way, is one of the world’s only predaceous butterfly caterpillars. Both these predators adapt a pretty interesting hunting strategy: they cover themselves with the aphids’ own waxy fuzz. Thus disguised, they become veritable wolves in sheep’s clothing, hunkering down among the aphid colony and munching away.
But wait…the story doesn’t end here. The disguise adapted by these larvae isn’t so much to hide them from the aphids as it is to hide them from the aphids’ body guards. Like many aphids worldwide, woolly alder aphids have an arrangement with Ant Protective Services. If you find a colony of aphids, look closely and you will surely find ants nearby. These ants may look like simple shepherds, herding flocks of aphids and “milking” them for honeydew, but the arrangement isn’t quite so bucolic. Sure, the aphids squeeze out droplets of super sweet liquid (a by-product of the sap they sucked from the plant – more on this in a moment) when stroked by the ants’ antennae, and the ants then tote these droplets home for dinner, but in exchange for this the ants protect the colony from all intruders. Go ahead and stick your finger among the aphids and see what happens. Quickly your finger will be attacked by the nearest ants. So the clever costumes used by the lacewing and butterfly larvae do a pretty good job of tricking the ants. If you don’t believe it, consider this: some researchers introduced undisguised larvae to an aphid colony and the ants patrols effectively removed them from the scene.
The aphids get an additional benefit from the “milking” process mentioned above. As we all know, a steady diet of sugars isn’t nutritionally balanced; even aphids need some protein, especially when it comes time to reproduce. In order to acquire the necessary nutrition (nitrogen), the aphids consume more sugary sap than they need. Their systems then separate out the minute traces of nitrogen and excrete the excess sugars (honeydew). The nitrogen is then utilized in making the necessary proteins for reproduction.
And this brings us to the life cycle of the woolly alder aphid. When you gaze upon a colony of aphids coating the twigs and branches of your alders, you are looking naught but females. There won’t be a male in sight. This is because these insects reproduce asexually, via a process known as parthenogenesis. This system of reproduction is actually a lot more common than you’d think. Unlike many insects, the virgin female aphid gives birth to live young (no time and energy wasted in making eggs), all of which are daughters. In almost no time at all, the daughters are squeezing out girls of their own. This reproductive strategy has the advantage of producing individuals perfectly adapted for the host plant and its immediate environment. Some researcher with nothing better to do once calculated that one female aphid could give rise to over 600 BILLION clones of herself over the course of a single season! Thank goodness for predators, parasites, diseases and limited numbers of host plants, eh?
But, even this sort of perfection has its limits, and towards the end of the summer, the host plant may be weakening, or the colony just needs to move on (perhaps the host is getting too crowded). Things become stressful and suddenly a generation is produced that has males. You will know this has happened when the formerly stationary insects have produced models with wings. The resources are now available for sexual reproduction, which results in the mixing up of genetic material. This in turn produces offspring that may be better able to survive conditions in other locations, so off they go. Natural selection will then determine which ones will survive.
What an amazing world we live in. Every time you turn around there is something new to discover. Who knew that white fuzz on a shrub could turn out to be so strange and exotic! I love science fiction, but part of me really believes that we don’t need to travel the expanses of the universe to find bizarre lifeforms: they are already here and living among us. So go forth, ye citizens of Earth, and see what fantastic lives you can uncover right in your own back yard!