Birch Catkin Bug: Stinky Bugs Falling From Trees

Question

My birch trees are infested with bugs. They hang in a cluster at the end of the branches. While gardening, they fall off the branches into my hair…and they stink! When you touch them, they leave a characteristic odor. When fall comes, they scatter all over my garden and especially into the lawn. What to do? Is there a bird that feeds on this pest?

Answer

This is probably the birch catkin bug (Kleidocerys resedae), a type of aptly named stink bug. It’s a very common insect in temperate regions of the northern hemisphere. It’s more disturbing than dangerous, because it mainly attacks birch catkins. And, since they’re not the main attraction of the plant, many people never even notice the little pests.

Sometimes it’s present in such large numbers that it runs out of catkins and then attacks your birch trees’ foliage. This is only late in the season when the tree has essentially already stocked up for the winter. Also yes, they wander onto lawns and other plants, but don’t do any damage there and you can just ignore them.

Oddly, while you find the birch catkin bugs stinks, I find the smell, although intense, quite pleasant, with a hint of wintergreen. But you didn’t mention another unpleasant aspect of the insect, so you’ve been lucky in that aspect. Because many people complain it enters the house in the fall, especially if there are birches near the structure. But here again, this pest remains more an annoyance than a serious problem. Once indoors, they soon die. There isn’t much they can feed on indoors: they really are restricted to birches.

In general, birds are not fond of this insect. Its smell repels them. But there are smaller natural predators (mites, fungi, etc.) that regularly raid, reducing the population to near zero. Thus the insect becomes cyclical. After two or three years of infestation, a predator settles in and then the population drops drastically.

How to Treat a Birch Catkin Bug Infestation

• First, it may be time to remove some lower branches from your birches so that you can walk freely around your garden without brushing against leaves or branches.
• Also, this insect won’t tolerate soapy water: strong squirts of an insecticidal soap solution will help a lot in controlling serious infestations.
• In addition, good basic care for birches (watering during periods of drought, thorough mulching at their base, moderate but regular fertilization, etc.) helps them build up resistance to insects in general and to birch catkin bugs in particular.
• Finally, as the insect often overwinters in plant debris at the foot of the host tree, attention to cleanliness will help. You could, for example, run fallen birch leaves through a shredder before using them as mulch. That will kill the adults and leave their bodies to enrich the soil.