One of the reasons I chose my house was the giant maple tree by the front porch. The foliage provides shade and privacy in the summer and a terrific Halloween backdrop in the fall. So, a few weeks ago, when I noticed the tree was infested with something, I was a bit concerned. Ok, maybe that’s putting it lightly. I threw science out the window and freaked out. “The tree’s covered with insects! It’s gonna die! Ew!! Call somebody! Quick!”
The homeowner’s association sent out an arborist to take a look, and I received a message back: “They aren’t harmful to the tree, and they’ll be gone soon.” That was it. Still rather grossed out, I went out with the garden hose. Maybe if they are almost done, I can help some of them go, I thought, or at least clean off the sticky residue left around. (The stickiness was attracting wasps, or so I thought. More of my un-scientific conclusions.)
I started to spray the tree. The hose kinked, so I walked up the steps, under the thickest branches, to untangle it. That was when something landed on my leg. I went from being a concerned gardener to a hysterical little girl. “EWW! There’s a bug on me! Get it off! Get it off!” (Ok, it was a bad moment–don’t tell anyone.)
I looked down. Lo and behold, the creature clinging to my leg for dear life was a lady beetle. Surprised, I shut off the hose and looked up. Sure enough, they were everywhere. My tree was infested with a gardener’s best friend. My scientific eye returned, and I began to look at the tree in a whole new light.
Ironically, I’d been looking for lady beetles. Awhile back, I used them as the inspiration for the Friday Fractal, and talked a bit about their viscous predatory nature. I also recommended buying locally captured swarms as organic pest control in the garden. I wanted to take my own advice, in hopes of saving my ailing columbine. My local store was out of the beetles, so I settled for an organic spray. It killed the plant–the aphids survived. Little did I know (at the time) a massive colony of aphid assassins was just around the corner.
There were probably aphids on the maple tree, too. Female lady beetles only lay their eggs near a source of food. They’ll lay anywhere between 20 to over a thousand yellow eggs, in clusters, usually on the undersides of leaves where they can be protected from climate and other predators. (We’ll get to those.) It probably took a number of beetles to lay the staggering number of eggs on my tree.
Many of the eggs never hatched. Those were the ill-fated male beetles. Some species of lady beetles, like the two-spotted variety (Adalia bipuncta) on my tree, contain symbiotic bacteria which kills the male embryos. A. bipuncta has been known to harbor three different types of symbiotic bacteria: Spiroplasma, Wolbochia, and Rickettsia. There is an adaptive bonus to this process, both for the bacteria and the lady beetles. The bacteria cannot be passed on through the male–only females can continue the line. This is a plus for the surviving females–they just eat their little unborn brothers. (Not very lady-like, I’ll admit.)
Once hatched (and fed) the lady beetle larvae are highly active. They start about the size of the eye of needle. Usually, within a month, they’ve molted four times, each time increasing in size. (They look like fuzzy spotted alligators… it was hard to get a picture of the larger ones, as they can move–fast.) At their largest, the larvae are less than a half a centimeter long:
When the larvae are fully grown, they attach themselves to some sturdy spot and develop into a pupa. These were a bit easier to photograph than the mobile larvae. I found pupae on the house, pupae on the bushes… pupae all over the place. (My 5-year old giggles every time I say that.) After about a week, an adult lady beetle emerges.
Some of the emerging lady beetles on my tree were a deep golden hue. I’m not sure if they deepen in color as they age, or if it is a genetic trait. (The blond-headed stepchildren in a family of redheads?)
Of course, the tree isn’t exactly a lady beetle paradise. Remember the wasps I mentioned? They aren’t attracted to the residue from the larvae. They’re attracted to the larvae. I’ve watched in rapt horror and fascination as these wasps prey on the beetles. They are nearly as prolific as the emerging lady beetles, constantly swarming around looking for an easy snack.
A. bipuncta is a common species in North America, native to Colorado. The same doesn’t hold true for the wasps dining on lady beetle larvae. The European paper wasps (Polistes dominulus) are new to town. I first encountered them a few years ago when they built a nest inside one of my birdhouses. The nest has since moved, but they’ve hung nearby to drink from my pond ever since. Now they hunt the native lady beetles.
There is already a little concern about the native species of lady beetles, like A. bipuncta. Some fear they may be displaced by European varieties (like the lady beetle I based a fractal on, Coccinella septempunctata.) These were introduced along the east coast during the1970s as pest control agents. The new types are more effective predators than the natives. With European wasps hunting the native populations, as well, a balance might be difficult to maintain.
The wasps, the beetles, the symbiotic bacteria, the aphids, the maple tree, and I all manage to get by now. I no longer get the creeps while walking under the tree. Instead of trying to hose them off, I now hope that some of the beetles (and their parasites and symbiots) will stick around over the winter.
All images above, taken by the author, can be viewed full size in a new window, just by clicking. For more general information about the reproductive cycle of the lady beetle, try this page.