Just one week into fall, the harvest has begun, but there’s something missing — the multi-colored Asian Lady Beetle. In some years they’ve already started invading towns and houses by now, though Iowa State University Professor of Entomology Donald Lewis advises patience.
The reason we’re not seeing them is that they haven’t started migrating. While shorter days are their cue to do that, the sunlight isn’t yet brief enough to convince them to leave the gardens and trees where they’re living, and feeding on aphids. This year there are fewer aphids in the farm fields, and Lewis says that may have limited the number of ladybugs.
Professor Lewis says there’s also a set of temperature cues that’ll send the lady beetles into their migration. For a time he thought it was specific: the first 80-degree day after autumn’s first freeze. It isn’t always that precise, but he says it seems to happen when temps get up into the 70s and 80s the ladybugs will be more active than during our chill days of early fall. He figures we’ll see them taking off “on a hot, sunny day in the middle of October.” He says they have no natural predators – and he says there’s a good reason. They smell bad.
“They just taste bad,” he declares, as bad as they smell to predators like birds and frogs. That protects them against some natural enemies, and though there are some small ones — tiny parasites that live in their bodies — the ladybugs beat them off by reproducing too fast, during the two generations they manage in the length of one summer. Lewis says while homeowners may dread their fall invasion, the lady beetles eat other pests and are what he calls “ecologically beneficial.”