Question: We often find large, dark beetles beneath rocks and plant debris in our garden. What are these? Are they harmful?

Answer: Based on your description, they are most likely predacious ground beetles. They range from 1/8 inch to 1 1/2 inches long, and are generally dark in color (dark brown to black). They are fast moving insects, which generally have prominent, long legs and fairly thread-like antennae. They hide under logs, rocks, or in soil crevices during the day because they are largely nocturnal animals that feed at night. 

Most ground beetles in this area feed on a varied diet of insects and insect-like creatures, many of which are garden or house pests, such as cutworms or house fly maggots. One specific group of ground beetles feeds on slugs and snails. Some occasionally feed on earthworms, but their beneficial feeding habits in general, far outweigh any detrimental effects they may have on local earthworm populations. 

Ground beetles go through egg, larval, and pupal stages of development before reaching adulthood. Development from the egg to the adult stage generally takes about a year. Some adults may live two to three years. The adults of some species lay their eggs in specially constructed mud or twig cells, while others lay their eggs in debris.

Ground beetles are often the victims of broad spectrum insecticides used around the home and garden. Avoid using insecticides when and where they are not truly needed. Mix only enough pesticides to cover the target plant. Do not allow pesticides to drift onto large areas of the ground where these beneficial insects live.

Question: Is it too late to apply a dormant spray to our fruit trees? They have not leafed out yet?

Answer: One of the most effective sprays for insect control is the so-called delayed dormant spray. The material applied is a horticultural spray oil which acts as a "contact" insecticide. It interferes physically rather than chemically with insect pests. These oils are fairly broad spectrum, controlling scales, mites, plant bugs, psyllids, certain moths, mealy bugs, some aphids, tent caterpillars and webworms. Horticultural oils applied now work by simply smothering over-wintering insect pests that cling to tree and shrub branches.

Previously, oil sprays were always called dormant oils because they could only be used when plants were dormant. Now, they are more refined and can be used on plants during the growing season as well. Be sure to follow labeled directions to insure safe use and appropriate timing,

Question: We simply can't believe it! We have caterpillars in our fir tree! We thought for sure the cold weather would have killed them, but they appear to have thrived on it. What are they? Should we spray them with something?

Answer: Based on your description, the caterpillars you are referring to are most likely silver spotted tiger moths. These insects are common throughout Western Washington. The main host for silver spotted tiger moth is Douglas fir, but it is also known to feed on spruce, pine and other conifers.

The chewing damage caused by these insects is limited and usually not very serious. The damage is not unique; it is consistent with that of other caterpillars. Aside from the chewing damage, the presence of these caterpillars is most detectable by their gregarious nature and by dense webbing on branches. These "tents" are somewhat similar to those of tent caterpillars--- a pest that does not feed on conifers. These tents and the caterpillars within appear on trees from now until spring.

The caterpillars continue to feed throughout the cold winter months eventually reaching about 1 1/2 inches long. They are covered with a combination of dense black reddish brown and yellowish hairs that may cause a rash or dermatitis upon contact. In most cases simply pruning out the infested branches and destroying the caterpillars provides an effective control. 

EDITOR'S NOTE: For answers to local gardening questions, contact Master Gardener Earl Miller at 642-0541 or e-mail hm at

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